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Public-key cryptography
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Public key cryptography, or asymmetric cryptography, is any cryptographic system that uses pairs of keys: public keys which may be disseminated widely, and private keys which are known only to the owner. This accomplishes two functions: authentication, which is when the public key is used to verify that a holder of the paired private key sent the message, and encryption, whereby only the holder of the paired private key can decrypt the message encrypted with the public key.
In a public key encryption system, any person can encrypt a message using the public key of the receiver, but such a message can be decrypted only with the receiver's private key. For this to work it must be computationally easy for a user to generate a public and private key-pair to be used for encryption and decryption. The strength of a public key cryptography system relies on the degree of difficulty (computational impracticality) for a properly generated private key to be determined from its corresponding public key. Security then depends only on keeping the private key private, and the public key may be published without compromising security.[1]
Public key cryptography systems often rely on cryptographic algorithms based on mathematical problems that currently admit no efficient solution — particularly those inherent in certain integer factorization, discrete logarithm, and elliptic curve relationships. Public key algorithms, unlike symmetric key algorithms, do not require a secure channel for the initial exchange of one (or more) secret keys between the parties. [2]
Because of the computational complexity of asymmetric encryption, it is usually used only for small blocks of data, typically the transfer of a symmetric encryption key (e.g. a session key). This symmetric key is then used to encrypt the rest of the potentially long message sequence. The symmetric encryption/decryption is based on simpler algorithms and is much faster.[3]
In a public key signature system, a person can combine a message with a private key to create a short digital signature on the message. Anyone with the corresponding public key can combine a message, a putative digital signature on it, and a known public key to verify whether the signature was valid—made by the owner of the corresponding private key. Changing the message, even replacing a single letter, will cause verification to fail: in a secure signature system, it is computationally infeasible for anyone who does not know the private key to deduce it from the public key or from any number of signatures, or to find a valid signature on any message for which a signature has not hitherto been seen. Thus the authenticity of a message can be demonstrated by the signature, provided the owner of the private key keeps the private key secret.[4][5]
Public key algorithms are fundamental security ingredients in cryptosystems, applications and protocols. They underpin various Internet standards, such as Transport Layer Security (TLS), S/MIME, PGP, and GPG. Some public key algorithms provide key distribution and secrecy (e.g., Diffie–Hellman key exchange), some provide digital signatures (e.g., Digital Signature Algorithm), and some provide both (e.g., RSA).
Public key cryptography finds application in, among others, the information technology security discipline, information security. Information security (IS) is concerned with all aspects of protecting electronic information assets against security threats.[6] Public key cryptography is used as a method of assuring the confidentiality, authenticity and non-repudiability of electronic communications and data storage.
Two of the best-known uses of public key cryptography are:
- Public key encryption, in which a message is encrypted with a recipient's public key. The message cannot be decrypted by anyone who does not possess the matching private key, who is thus presumed to be the owner of that key and the person associated with the public key. This is used in an attempt to ensure confidentiality.
- Digital signatures, in which a message is signed with the sender's private key and can be verified by anyone who has access to the sender's public key. This verification proves that the sender had access to the private key, and therefore is likely to be the person associated with the public key. This also ensures that the message has not been tampered with, as a signature is mathematically bound to the message it originally was made with, and verification will fail for practically any other message, no matter how similar to the original message.
An analogy to public key encryption is that of a locked mail box with a mail slot. The mail slot is exposed and accessible to the public – its location (the street address) is, in essence, the public key. Anyone knowing the street address can go to the door and drop a written message through the slot. However, only the person who possesses the key can open the mailbox and read the message.
An analogy for digital signatures is the sealing of an envelope with a personal wax seal. The message can be opened by anyone, but the presence of the unique seal authenticates the sender.
A central problem with the use of public key cryptography is confidence/proof that a particular public key is authentic, in that it is correct and belongs to the person or entity claimed, and has not been tampered with or replaced by a malicious third party. The usual approach to this problem is to use a public key infrastructure (PKI), in which one or more third parties – known as certificate authorities – certify ownership of key pairs. PGP, in addition to being a certificate authority structure, has used a scheme generally called the "web of trust", which decentralizes such authentication of public keys by a central mechanism, and substitutes individual endorsements of the link between user and public key. To date, no fully satisfactory solution to the "public key authentication problem" has been found.[citation needed]
During the early history of cryptography, two parties would rely upon a key that they would exchange by means of a secure, but non-cryptographic, method such as a face-to-face meeting or a trusted courier. This key, which both parties kept absolutely secret, could then be used to exchange encrypted messages. A number of significant practical difficulties arise with this approach to distributing keys.
In his 1874 book The Principles of Science, William Stanley Jevons[7] wrote:
Can the reader say what two numbers multiplied together will produce the number 8616460799?[8] I think it unlikely that anyone but myself will ever know.[9]
Here he described the relationship of one-way functions to cryptography, and went on to discuss specifically the factorization problem used to create a trapdoor function. In July 1996, mathematician Solomon W. Golomb said: "Jevons anticipated a key feature of the RSA Algorithm for public key cryptography, although he certainly did not invent the concept of public key cryptography."[10] (In 1869, Jevons had also invented a computing machine he called a "Logic Piano".)
Classified discovery
In 1970, James H. Ellis, a British cryptographer at the UK Government Communications Headquarters (GCHQ), conceived of the possibility of "non-secret encryption", (now called public key cryptography), but could see no way to implement it.[11] In 1973, his colleague Clifford Cocks implemented what has become known as the RSA encryption algorithm, giving a practical method of "non-secret encryption", and in 1974, another GCHQ mathematician and cryptographer, Malcolm J. Williamson, developed what is now known as Diffie–Hellman key exchange. The scheme was also passed to the USA's National Security Agency.[12] With a military focus, and low computing power, the power of public key cryptography was unrealised in both organisations:
I judged it most important for military use ... if you can share your key rapidly and electronically, you have a major advantage over your opponent. Only at the end of the evolution from Berners-Lee designing an open internet architecture for CERN, its adaptation and adoption for the Arpanet ... did public key cryptography realise its full potential.
Their discovery did not become public knowledge for 27 years, until the research was declassified by the British government in 1997.[13]
Public discovery
In 1976, an asymmetric key cryptosystem was published by Whitfield Diffie and Martin Hellman who, influenced by Ralph Merkle's work on public key distribution, disclosed a method of public key agreement. This method of key exchange, which uses exponentiation in a finite field, came to be known as Diffie–Hellman key exchange. This was the first published practical method for establishing a shared secret-key over an authenticated (but not confidential) communications channel without using a prior shared secret. Merkle's "public key-agreement technique" became known as Merkle's Puzzles, and was invented in 1974 and published in 1978.
In 1977, a generalization of Cocks' scheme was independently invented by Ron Rivest, Adi Shamir and Leonard Adleman, all then at MIT. The latter authors published their work in 1978, and the algorithm came to be known as RSA, from their initials. RSA uses exponentiation modulo a product of two very large primes, to encrypt and decrypt, performing both public key encryption and public key digital signature. Its security is connected to the extreme difficulty of factoring large integers, a problem for which there is no known efficient general technique. In 1979, Michael O. Rabin published a related cryptosystem that is probably secure as long as the factorization of the public key remains difficult – it remains an assumption that RSA also enjoys this security.
Since the 1970s, a large number and variety of encryption, digital signature, key agreement, and other techniques have been developed in the field of public key cryptography. The ElGamal cryptosystem, invented by Taher ElGamal relies on the similar and related high level of difficulty of the discrete logarithm problem, as does the closely related DSA, which was developed at the US National Security Agency (NSA) and published by NIST as a proposed standard.
The introduction of elliptic curve cryptography by Neal Koblitz and Victor Miller, independently and simultaneously in the mid-1980s, has yielded new public key algorithms based on the discrete logarithm problem. Although mathematically more complex, elliptic curves provide smaller key sizes and faster operations for approximately equivalent estimated security.
Typical use
Public key cryptography is often used to secure electronic communication over an open networked environment such as the Internet, without relying on a hidden or covert channel, even for key exchange. Open networked environments are susceptible to a variety of communication security problems, such as man-in-the-middle attacks and spoofs. Communication security typically includes requirements that the communication must not be readable during transit (preserving confidentiality), the communication must not be modified during transit (preserving the integrity of the communication), the communication must originate from an identified party (sender authenticity), and the recipient must not be able to repudiate or deny receiving the communication. Combining public key cryptography with an Enveloped Public Key Encryption (EPKE)[14] method, allows for the secure sending of a communication over an open networked environment. In other words, even if an adversary listens to an entire conversation including the key exchange, the adversary would not be able to interpret the conversation.
The distinguishing technique used in public key cryptography is the use of asymmetric key algorithms, where a key used by one party to perform encryption is not the same as the key used by another in decryption. Each user has a pair of cryptographic keys – a public encryption key and a private decryption key. For example, a key pair used for digital signatures consists of a private signing key and a public verification key. The public key may be widely distributed, while the private key is known only to its proprietor. The keys are related mathematically, but the parameters are chosen so that calculating the private key from the public key is unfeasible.
In contrast, symmetric key algorithms use a single secret key, which must be shared and kept private by both the sender (for encryption) and the receiver (for decryption). To use a symmetric encryption scheme, the sender and receiver must securely share a key in advance.
Because symmetric key algorithms are nearly always much less computationally intensive than asymmetric ones, it is common to exchange a key using a key-exchange algorithm, then transmit data using that key and a symmetric key algorithm. PGP and the SSL/TLS family of schemes use this procedure, and are thus called hybrid cryptosystems.
Some encryption schemes can be proven secure on the basis of the presumed difficulty of a mathematical problem, such as factoring the product of two large primes or computing discrete logarithms. Note that "secure" here has a precise mathematical meaning, and there are multiple different (meaningful) definitions of what it means for an encryption scheme to be "secure". The "right" definition depends on the context in which the scheme will be deployed.
The most obvious application of a public key encryption system is confidentiality – a message that a sender encrypts using the recipient's public key can be decrypted only by the recipient's paired private key. This assumes, of course, that no flaw is discovered in the basic algorithm used.
Another application in public key cryptography is the digital signature. Digital signature schemes can be used for sender authentication and non-repudiation. The sender computes a digital signature for the message to be sent, then sends the signature (together with the message) to the intended receiver. Digital signature schemes have the property that signatures can be computed only with the knowledge of the correct private key. To verify that a message has been signed by a user and has not been modified, the receiver needs to know only the corresponding public key. In some cases (e.g., RSA), a single algorithm can be used to both encrypt and create digital signatures. In other cases (e.g., DSA), each algorithm can only be used for one specific purpose.
To achieve both authentication and confidentiality, the sender should include the recipient's name in the message, sign it using his private key, and then encrypt both the message and the signature using the recipient's public key.
These characteristics can be used to construct many other (sometimes surprising) cryptographic protocols and applications, such as digital cash, password-authenticated key agreement, multi-party key agreement, time-stamping services, non-repudiation protocols, etc.
Practical considerations
Enveloped Public Key Encryption
Enveloped Public Key Encryption (EPKE) is the method of applying public key cryptography and ensuring that an electronic communication is transmitted confidentially, has the contents of the communication protected against being modified (communication integrity) and cannot be denied from having been sent (non-repudiation). This is often the method used when securing communication on an open networked environment such by making use of the Transport Layer Security (TLS) or Secure Sockets Layer (SSL) protocols.
EPKE consists of a two-stage process that includes both Public Key Encryption (PKE) and a digital signature. Both Public Key Encryption and digital signatures make up the foundation of Enveloped Public Key Encryption (these two processes are described in full in their own sections).
For EPKE to work effectively, it is required that:
- Every participant in the communication has their own unique pair of keys. The first key that is required is a public key and the second key that is required is a private key.
- Each person's own private and public keys must be mathematically related where the private key is used to decrypt a communication sent using a public key and vice versa. Some well-known asymmetric encryption algorithms are based on the RSA cryptosystem.
- The private key must be kept absolutely private by the owner, though the public key can be published in a public directory such as with a certification authority.
To send a message using EPKE, the sender of the message first signs the message using their own private key, this ensures non-repudiation of the message. The sender then encrypts their digitally signed message using the receiver's public key thus applying a digital envelope to the message. This step ensures confidentiality during the transmission of the message. The receiver of the message then uses their private key to decrypt the message thus removing the digital envelope and then uses the sender's public key to decrypt the sender's digital signature. At this point, if the message has been unaltered during transmission, the message will be clear to the receiver.
Due to the computationally complex nature of RSA-based asymmetric encryption algorithms, the time taken to encrypt large documents or files to be transmitted can be relatively long. To speed up the process of transmission, instead of applying the sender's digital signature to the large documents or files, the sender can rather hash the documents or files using a cryptographic hash function and then digitally sign the generated hash value, therefore enforcing non-repudiation. Hashing is a much faster computation to complete as opposed to using an RSA-based digital signature algorithm alone. The sender would then sign the newly generated hash value and encrypt the original documents or files with the receiver's public key. The transmission would then take place securely and with confidentiality and non-repudiation still intact. The receiver would then verify the signature and decrypt the encrypted documents or files with their private key.
Note: The sender and receiver do not usually carry out the process mentioned above manually though, but rather rely on sophisticated software to automatically complete the EPKE process.
Public Key Encryption
The goal of Public Key Encryption (PKE) is to ensure that the communication being sent is kept confidential during transit.
To send a message using PKE, the sender of the message uses the public key of the receiver to encrypt the contents of the message. The encrypted message is then transmitted electronically to the receiver and the receiver can then use their own matching private key to decrypt the message.
The encryption process of using the receiver's public key is useful for preserving the confidentiality of the message as only the receiver has the matching private key to decrypt the message. Therefore, the sender of the message cannot decrypt the message once it has been encrypted using the receiver's public key. However, PKE does not address the problem of non-repudiation, as the message could have been sent by anyone that has access to the receiver's public key.
Digital signatures
Template:Main article A digital signature is meant to prove a message came from a particular sender; neither can anyone impersonate the sender nor can the sender deny having sent the message. This is useful for example when making an electronic purchase of shares, allowing the receiver to prove who requested the purchase. Digital signatures do not provide confidentiality for the message being sent.
The message is signed using the sender's private signing key. The digitally signed message is then sent to the receiver, who can then use the sender's public key to verify the signature.
In order for Enveloped Public Key Encryption to be as secure as possible, there needs to be a "gatekeeper" of public and private keys, or else anyone could create key pairs and masquerade as the intended sender of a communication, proposing them as the keys of the intended sender. This digital key "gatekeeper" is known as a certification authority. A certification authority is a trusted third party that can issue public and private keys, thus certifying public keys. It also works as a depository to store key chain and enforce the trust factor.
Postal analogies
An analogy that can be used to understand the advantages of an asymmetric system is to imagine two people, Alice and Bob, who are sending a secret message through the public mail. In this example, Alice wants to send a secret message to Bob, and expects a secret reply from Bob.
With a symmetric key system, Alice first puts the secret message in a box, and locks the box using a padlock to which she has a key. She then sends the box to Bob through regular mail. When Bob receives the box, he uses an identical copy of Alice's key (which he has somehow obtained previously, maybe by a face-to-face meeting) to open the box, and reads the message. Bob can then use the same padlock to send his secret reply.
In an asymmetric key system, Bob and Alice have separate padlocks. First, Alice asks Bob to send his open padlock to her through regular mail, keeping his key to himself. When Alice receives it she uses it to lock a box containing her message, and sends the locked box to Bob. Bob can then unlock the box with his key and read the message from Alice. To reply, Bob must similarly get Alice's open padlock to lock the box before sending it back to her.
The critical advantage in an asymmetric key system is that Bob and Alice never need to send a copy of their keys to each other. This prevents a third party – perhaps, in this example, a corrupt postal worker who opens unlocked boxes – from copying a key while it is in transit, allowing the third party to spy on all future messages sent between Alice and Bob. So, in the public key scenario, Alice and Bob need not trust the postal service as much. In addition, if Bob were careless and allowed someone else to copy his key, Alice's messages to Bob would be compromised, but Alice's messages to other people would remain secret, since the other people would be providing different padlocks for Alice to use.
Another kind of asymmetric key system, called a three-pass protocol, requires neither party to even touch the other party's padlock (or key to get access); Bob and Alice have separate padlocks.
First, Alice puts the secret message in a box, and locks the box using a padlock to which only she has a key. She then sends the box to Bob through regular mail. When Bob receives the box, he adds his own padlock to the box, and sends it back to Alice. When Alice receives the box with the two padlocks, she removes her padlock and sends it back to Bob. When Bob receives the box with only his padlock on it, Bob can then unlock the box with his key and read the message from Alice. Note that, in this scheme, the order of decryption is NOT the same as the order of encryption – this is only possible if commutative ciphers are used. A commutative cipher is one in which the order of encryption and decryption is interchangeable, just as the order of multiplication is interchangeable (i.e.,
A*B*C = A*C*B = C*B*A). This method is secure for certain choices of commutative ciphers, but insecure for others (e.g., a simple
XOR). For example, let
E1() and
E2() be two encryption functions, and let "
M" be the message so that if Alice encrypts it using
E1() and sends
E1(M) to Bob. Bob then again encrypts the message as
E2(E1(M)) and sends it to Alice. Now, Alice decrypts
E2(E1(M)) using
E1(). Alice will now get
E2(M), meaning when she sends this again to Bob, he will be able to decrypt the message using
E2() and get "
M". Although none of the keys were ever exchanged, the message "
M" may well be a key (e.g., Alice's Public key). This three-pass protocol is typically used during key exchange.
Actual algorithms: two linked keys
Not all asymmetric key algorithms operate in this way. In the most common, Alice and Bob each own two keys, one for encryption and one for decryption. In a secure asymmetric key encryption scheme, the private key should not be deducible from the public key. This makes possible public key encryption, since an encryption key can be published without compromising the security of messages encrypted with that key.
In other schemes, either key can be used to encrypt the message. When Bob encrypts a message with his private key, only his public key will successfully decrypt it, authenticating Bob's authorship of the message. In the alternative, when a message is encrypted with the public key, only the private key can decrypt it. In this arrangement, Alice and Bob can exchange secret messages with no prior secret agreement, each using the other's public key to encrypt, and each using his own to decrypt.
Among symmetric key encryption algorithms, only the one-time pad can be proven to be secure against any adversary – no matter how much computing power is available. However, there is no public key scheme with this property, since all public key schemes are susceptible to a "brute-force key search attack". Such attacks are impractical if the amount of computation needed to succeed – termed the "work factor" by Claude Shannon – is out of reach of all potential attackers. In many cases, the work factor can be increased by simply choosing a longer key. But other algorithms may have much lower work factors, making resistance to a brute-force attack irrelevant. Some special and specific algorithms have been developed to aid in attacking some public key encryption algorithms – both RSA and ElGamal encryption have known attacks that are much faster than the brute-force approach. These factors have changed dramatically in recent decades, both with the decreasing cost of computing power and with new mathematical discoveries.
Aside from the resistance to attack of a particular key pair, the security of the certification hierarchy must be considered when deploying public key systems. Some certificate authority – usually a purpose-built program running on a server computer – vouches for the identities assigned to specific private keys by producing a digital certificate. Public key digital certificates are typically valid for several years at a time, so the associated private keys must be held securely over that time. When a private key used for certificate creation higher in the PKI server hierarchy is compromised, or accidentally disclosed, then a "man-in-the-middle attack" is possible, making any subordinate certificate wholly insecure.
Major weaknesses have been found for several formerly promising asymmetric key algorithms. The 'knapsack packing' algorithm was found to be insecure after the development of a new attack. Recently, some attacks based on careful measurements of the exact amount of time it takes known hardware to encrypt plain text have been used to simplify the search for likely decryption keys (see "side channel attack"). Thus, mere use of asymmetric key algorithms does not ensure security. A great deal of active research is currently underway to both discover, and to protect against, new attack algorithms.
Another potential security vulnerability in using asymmetric keys is the possibility of a "man-in-the-middle" attack, in which the communication of public keys is intercepted by a third party (the "man in the middle") and then modified to provide different public keys instead. Encrypted messages and responses must also be intercepted, decrypted, and re-encrypted by the attacker using the correct public keys for different communication segments, in all instances, so as to avoid suspicion. This attack may seem to be difficult to implement in practice, but it is not impossible when using insecure media (e.g., public networks, such as the Internet or wireless forms of communications) – for example, a malicious staff member at Alice or Bob's Internet Service Provider (ISP) might find it quite easy to carry out. In the earlier postal analogy, Alice would have to have a way to make sure that the lock on the returned packet really belongs to Bob before she removes her lock and sends the packet back. Otherwise, the lock could have been put on the packet by a corrupt postal worker pretending to be Bob, so as to fool Alice.
One approach to prevent such attacks involves the use of a certificate authority, a trusted third party responsible for verifying the identity of a user of the system. This authority issues a tamper-resistant, non-spoofable digital certificate for the participants. Such certificates are signed data blocks stating that this public key belongs to that person, company, or other entity. This approach also has its weaknesses – for example, the certificate authority issuing the certificate must be trusted to have properly checked the identity of the key-holder, must ensure the correctness of the public key when it issues a certificate, must be secure from computer piracy, and must have made arrangements with all participants to check all their certificates before protected communications can begin. Web browsers, for instance, are supplied with a long list of "self-signed identity certificates" from PKI providers – these are used to check the bona fides of the certificate authority and then, in a second step, the certificates of potential communicators. An attacker who could subvert any single one of those certificate authorities into issuing a certificate for a bogus public key could then mount a "man-in-the-middle" attack as easily as if the certificate scheme were not used at all. In an alternate scenario rarely discussed, an attacker who penetrated an authority's servers and obtained its store of certificates and keys (public and private) would be able to spoof, masquerade, decrypt, and forge transactions without limit.
Despite its theoretical and potential problems, this approach is widely used. Examples include SSL and its successor, TLS, which are commonly used to provide security for web browser transactions (for example, to securely send credit card details to an online store).
Computational cost
The public key algorithms known thus far are relatively computationally costly compared with most symmetric key algorithms of apparently equivalent security. The difference factor is the use of typically quite large keys. This has important implications for their practical use. Most are used in hybrid cryptosystems for reasons of efficiency – in such a cryptosystem, a shared secret key ("session key") is generated by one party, and this much briefer session key is then encrypted by each recipient's public key. Each recipient then uses his own private key to decrypt the session key. Once all parties have obtained the session key, they can use a much faster symmetric algorithm to encrypt and decrypt messages. In many of these schemes, the session key is unique to each message exchange, being pseudo-randomly chosen for each message.
Associating public keys with identities
The binding between a public key and its "owner" must be correct, or else the algorithm may function perfectly and yet be entirely insecure in practice. As with most cryptography applications, the protocols used to establish and verify this binding are critically important. Associating a public key with its owner is typically done by protocols implementing a public key infrastructure – these allow the validity of the association to be formally verified by reference to a trusted third party in the form of either a hierarchical certificate authority (e.g., X.509), a local trust model (e.g., SPKI), or a web of trust scheme, like that originally built into PGP and GPG, and still to some extent usable with them. Whatever the cryptographic assurance of the protocols themselves, the association between a public key and its owner is ultimately a matter of subjective judgment on the part of the trusted third party, since the key is a mathematical entity, while the owner – and the connection between owner and key – are not. For this reason, the formalism of a public key infrastructure must provide for explicit statements of the policy followed when making this judgment. For example, the complex and never fully implemented X.509 standard allows a certificate authority to identify its policy by means of an object identifier, which functions as an index into a catalog of registered policies. Policies may exist for many different purposes, ranging from anonymity to military classifications.
Relation to real world events
A public key will be known to a large and, in practice, unknown set of users. All events requiring revocation or replacement of a public key can take a long time to take full effect with all who must be informed (i.e., all those users who possess that key). For this reason, systems that must react to events in real time (e.g., safety-critical systems or national security systems) should not use public key encryption without taking great care. There are four issues of interest:
Privilege of key revocation
A malicious (or erroneous) revocation of some (or all) of the keys in the system is likely, or in the second case, certain, to cause a complete failure of the system. If public keys can be revoked individually, this is a possibility. However, there are design approaches that can reduce the practical chance of this occurring. For example, by means of certificates, we can create what is called a "compound principal" – one such principal could be "Alice and Bob have Revoke Authority". Now, only Alice and Bob (in concert) can revoke a key, and neither Alice nor Bob can revoke keys alone. However, revoking a key now requires both Alice and Bob to be available, and this creates a problem of reliability. In concrete terms, from a security point of view, there is now a "single point of failure" in the public key revocation system. A successful Denial of Service attack against either Alice or Bob (or both) will block a required revocation. In fact, any partition of authority between Alice and Bob will have this effect, regardless of how it comes about.
Because the principle allowing revocation authority for keys is very powerful, the mechanisms used to control it should involve both as many participants as possible (to guard against malicious attacks of this type), while at the same time as few as possible (to ensure that a key can be revoked without dangerous delay). Public key certificates that include an expiration date are unsatisfactory in that the expiration date may not correspond with a real-world revocation but at least such certificates need not all be tracked down system-wide, nor must all users be in constant contact with the system at all times.
Distribution of a new key
After a key has been revoked, or when a new user is added to a system, a new key must be distributed in some predetermined manner. Assume that Carol's key has been revoked (e.g., by exceeding its expiration date, or because of a compromise of Carol's matching private key). Until a new key has been distributed, Carol is effectively "out of contact". No one will be able to send her messages without violating system protocols (i.e., without a valid public key, no one can encrypt messages to her), and messages from her cannot be signed, for the same reason. Or, in other words, the "part of the system" controlled by Carol is, in essence, unavailable. Security requirements have been ranked higher than system availability in such designs.
One could leave the power to create (and certify) keys (as well as to revoke them) in the hands of each user – the original PGP design did so – but this raises problems of user understanding and operation. For security reasons, this approach has considerable difficulties – if nothing else, some users will be forgetful, or inattentive, or confused. On the one hand, a message revoking a public key certificate should be spread as fast as possible, while on the other hand, parts of the system might be rendered inoperable before a new key can be installed. The time window can be reduced to zero by always issuing the new key together with the certificate that revokes the old one, but this requires co-location of authority to both revoke keys and generate new keys.
It is most likely a system-wide failure if the (possibly combined) principal that issues new keys fails by issuing keys improperly. This is an instance of a "common mutual exclusion" – a design can make the reliability of a system high, but only at the cost of system availability (and vice versa).
Spreading the revocation
Notification of a key certificate revocation must be spread to all those who might potentially hold it, and as rapidly as possible.
There are but two means of spreading information (i.e., a key revocation) in a distributed system: either the information is "pushed" to users from a central point (or points), or else it is "pulled" from a central point(or points) by the end users.
Pushing the information is the simplest solution, in that a message is sent to all participants. However, there is no way of knowing whether all participants will actually receive the message. If the number of participants is large, and some of their physical or network distances are great, then the probability of complete success (which is, in ideal circumstances, required for system security) will be rather low. In a partly updated state, the system is particularly vulnerable to "denial of service" attacks as security has been breached, and a vulnerability window will continue to exist as long as some users have not "gotten the word". Put another way, pushing certificate revocation messages is neither easy to secure, nor very reliable.
The alternative to pushing is pulling. In the extreme, all certificates contain all the keys needed to verify that the public key of interest (i.e., the one belonging to the user to whom one wishes to send a message, or whose signature is to be checked) is still valid. In this case, at least some use of the system will be blocked if a user cannot reach the verification service (i.e., one of the systems that can establish the current validity of another user's key). Again, such a system design can be made as reliable as one wishes, at the cost of lowering security – the more servers to check for the possibility of a key revocation, the longer the window of vulnerability.
Another trade-off is to use a somewhat less reliable, but more secure, verification service, but to include an expiration date for each of the verification sources. How long this "timeout" should be is a decision that requires a trade-off between availability and security that will have to be decided in advance, at the time of system design.
Recovery from a leaked key
Assume that the principal authorized to revoke a key has decided that a certain key must be revoked. In most cases, this happens after the fact – for instance, it becomes known that at some time in the past an event occurred that endangered a private key. Let us denote the time at which it is decided that the compromise occurred as T.
Such a compromise has two implications. First, messages encrypted with the matching public key (now or in the past) can no longer be assumed to be secret. One solution to avoid this problem is to use a protocol that has perfect forward secrecy. Second, signatures made with the no-longer-trusted-to-be-actually-private key after time T can no longer be assumed to be authentic without additional information (i.e., who, where, when, etc.) about the events leading up to the digital signature. These will not always be available, and so all such digital signatures will be less than credible. A solution to reduce the impact of leaking a private key of a signature scheme is to use timestamps.
Loss of secrecy and/or authenticity, even for a single user, has system-wide security implications, and a strategy for recovery must thus be established. Such a strategy will determine who has authority to, and under what conditions one must, revoke a public key certificate. One must also decide how to spread the revocation, and ideally, how to deal with all messages signed with the key since time T (which will rarely be known precisely). Messages sent to that user (which require the proper – now compromised – private key to decrypt) must be considered compromised as well, no matter when they were sent.
Examples of well-regarded asymmetric key techniques for varied purposes include:
- Diffie–Hellman key exchange protocol
- DSS (Digital Signature Standard), which incorporates the Digital Signature Algorithm
- ElGamal
- Various elliptic curve techniques
- Various password-authenticated key agreement techniques
- Paillier cryptosystem
- RSA encryption algorithm (PKCS#1)
- Cramer–Shoup cryptosystem
- YAK authenticated key agreement protocol
Examples of asymmetric key algorithms not widely adopted include:
- NTRUEncrypt cryptosystem
- McEliece cryptosystem
Examples of notable – yet insecure – asymmetric key algorithms include:
Examples of protocols using asymmetric key algorithms include:
- GPG, an implementation of OpenPGP
- Internet Key Exchange
- ZRTP, a secure VoIP protocol
- Secure Socket Layer, now codified as the IETF standard Transport Layer Security (TLS)
- Bitcoin
- Off-the-Record Messaging
See also
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- Books on cryptography
- GNU Privacy Guard
- ID-based encryption (IBE)
- Key escrow
- Key-agreement protocol
- PGP word list
- Pretty Good Privacy
- Pseudonymity
- Public key fingerprint
- Public key infrastructure (PKI)
- Quantum computers
- Quantum cryptography
- Secure Shell (SSH)
- Secure Sockets Layer (SSL)
- Symmetric-key algorithm
- Threshold cryptosystem
- Hirsch, Frederick J.. "SSL/TLS Strong Encryption: An Introduction". Apache HTTP Server. http://httpd.apache.org/docs/2.2/ssl/ssl_intro.html#cryptographictech. Retrieved 2013-04-17.. The first two sections contain a very good introduction to public-key cryptography.
- Template:Cite book
- Template:Cite book
- Template:Cite book
- IEEE 1363: Standard Specifications for Public-Key Cryptography
- Christof Paar, Jan Pelzl, "Introduction to Public-Key Cryptography", Chapter 6 of "Understanding Cryptography, A Textbook for Students and Practitioners". (companion web site contains online cryptography course that covers public-key cryptography), Springer, 2009.
External links
- Oral history interview with Martin Hellman, Charles Babbage Institute, University of Minnesota. Leading cryptography scholar Martin Hellman discusses the circumstances and fundamental insights of his invention of public key cryptography with collaborators Whitfield Diffie and Ralph Merkle at Stanford University in the mid-1970s.
- An account of how GCHQ kept their invention of PKE secret until 1997
Template:Cryptography navbox Template:SSL/TLS
- ↑ Template:Cite book
- ↑ See OTAR to contrast.
- ↑ Template:Cite book
- ↑ Template:Cite book
- ↑ Template:Cite journal
- ↑ "Information Security Resources". SANS Institute. http://www.sans.org/information-security. Retrieved 25 May 2014.
- ↑ Jevons, William Stanley, The Principles of Science: A Treatise on Logic and Scientific Method p. 141, Macmillan & Co., London, 1874, 2nd ed. 1877, 3rd ed. 1879. Reprinted with a foreword by Ernst Nagel, Dover Publications, New York, NY, 1958.
- ↑ This came to be known as "Jevons' number". The only nontrivial factor pair is 89681 × 96079.
- ↑ Principles of Science, Macmillan & Co., 1874, p. 141.
- ↑ Template:Cite journal
- ↑ Sawer, Patrick (11 Mar 2016). "The unsung genius who secured Britain's computer defences and paved the way for safe online shopping". The Telegraph. http://www.telegraph.co.uk/history/12191473/The-unsung-genius-who-secured-Britains-computer-defences-and-paved-the-way-for-safe-online-shopping.html.
- ↑ 12.0 12.1 Tom Espiner (October 26, 2010). "GCHQ pioneers on birth of public key crypto". http://www.zdnet.com/article/gchq-pioneers-on-birth-of-public-key-crypto/.
- ↑ Template:Cite book
- ↑ "What is a digital envelope?". RSA Laboratories. http://www.emc.com/emc-plus/rsa-labs/standards-initiatives/what-is-a-digital-envelope.htm. Retrieved 25 May 2014.


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Story highlights
The Scarborough Faire Renaissance Festival attracts nearly 250,000 period fans.
The festival has it's fair share of couple who wed dressed as Robin Hood and Maid Marian.
Frozen Dead Guy Days in Nederland, Colorado is dedicated to the frozen corpse of its oldest resident.
Attendees participate in coffin races and hearse parades.
As Paris Fashion Week demonstrates, adults love playing dress up just as much as children. The only difference between junior and senior would-be masters-of-disguise is that kids don't need an excuse to don a costume; grown-ups, however, seem to feel more comfortable when there's a theme involved. In the market for an outfit to match your fetish? With Halloween on the horizon, we've rounded up some of the craziest costumed events out there.
Getting geeky with it
Self-proclaimed (and a few closeted) nerds will find no shortage of events catering to the dweebiest of whims. Though it faces some stiff competition (the Roswell UFO Festival, which encourages participants to dress as their favorite alien, could give it a run for its money), Comic-Con is arguably the dorkiest event on the calendar. The San Diego variant is not only the original, it is also the biggest comic-related convention. Last year heralded in over 130,000 visitors, with costumes ranging from Stark Trek characters to comic super heroes and even the odd Disney princess. As it has become an 'it' event for any Hollywood franchise wishing to build a cult-following (and there's a lot of them), Comic-Con has even managed to make the geek a little bit chic over the years, with A-list celebs showing up in costume too.
Eyes Wide Shut
Fans of Stanley Kubrick should head to Italy to take part in one of the largest masked festivals on Earth. During Venice Carnevale, the "city without streets" takes on an especially surreal vibe as thousands of tourists join the locals in donning elaborate masks and gowns for ten days of celebrations. Though Carnevale's roots date back to the Middle Ages, the modern version has only been active since the '70s (blame Napoleon, who put an end to the fun when he invaded in 1797).
The city's Piazza San Marco becomes mobbed with tourists and photographers, who snap pics of professionals strutting their stuff in ornate robes and those creepy, bird-like masks the city is famous for.
Time travelers delight
At the Scarborough Faire Renaissance Festival, which runs every weekend throughout April and May, the 242,000 annual visitors are prone to dress in period outfits. The festival is set in 1533, the year Henry VIII married Anne Boleyn.
General manager Coy Sevier says that historically, during a royal wedding,the king and queen would tour all the villages in their realm. He notes that such an event makes a handy motif for a gathering dedicated to outrageous costumes.
"Of course, anytime the king comes to town, it's a good time to spruce up, put on your finest, and put on a good show," he says. Though the professional performers are held to a high standard, with costume guards making sure no detail is out of place, for everyone else, it's a free for all.
Read more: The man behind the world's strangest holidays
"We have guests that come in as Dr. Who. We have a whole selection of musketeers. Even though they're a couple hundred years off, they're more than welcome," he says.
The Vikings are coming!
The Shetland Islands in the UK is home to the world's largest fire festival, Up Helly Aa, which also happens to be a holdover from Viking times. As such, the event is celebrated with a procession of 1,000 "guizers", or men in Viking costume, making their way through the town of Lerwick until they reach the Valhalla, where they then toss lit torches into a Viking long ship.
Though dressing up is mainly reserved for locals, anyone is invited to witness the event. Last year, 5,000 onlookers cheered the helmeted mass as they readied themselves to take down another ship.
Unleash the dark
Lovers of the macabre will do well to visit Leipzing, Germany during the annual Wave-Gotik-Treffen, aka, the Wave and Goth Festival. The costumes are remarkably diverse; futuristic robots are as much the norm as darkly-clad, Byron-esque romantics. The one thing that seems to unify the 20,000 participants, however, is an affection for Goth culture (which just happens to be very varied).
"In the last few years, new music styles have developed within the scene. In many cases, fashion is connected to that specialist taste, which is why there's such a range," explains Cornelius Brach, the festival organizer.
Won't you join the (blue) ball?
In 1995, the small town of Nederland, Colorado (population 1,470) became an unintentional symbol for cryogenics. A few years earlier, the body of Norwegian citizen Bredo Morstøl was shipped out to the town to live stored in a frozen state in the home of his daughter, Aud Morstøl. When she was evicted for living in a house without electricity or plumbing, she went to the local press in the hopes of salvaging her father's remains.
Read more: The world's weirdest food festivals
Today, "Grandpa Bredo" (as he's known locally) is stored in a shed, packed with 1,600 pounds of dry ice delivered by a team of volunteers. In 2002, the town decided to commemorate the event with Frozen Dead Guy Days, an annual three-day homage to corpses and cold.
"We're a very small mountain town, and it's hard to eke out a living. The Chamber of Commerce was like, 'well, we're known as the town with the frozen dead guy, so let's have a festival,'" explains Amanda MacDonald, the event organizer.
Highlights of the fete include a coffin race, hearse parade, costume polar plunge and the Frozen Blue Ball – a necro-themed costume party. Though anything goes in terms of costumes, the theme tends to revolve around cold things. Penguins, says McDonald, are popular.

subset: commoncrawl


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Just five months into the £30 million refurbishment of the Fairfield Halls, and Croydon Council is already admitting that it will take longer than the promised two-year closure to complete the works.
With the main refurbishment contractor not due to start work for another six months, there's a strong possibility, according to one former council engineer, that the Fairfield Halls will now not open until 2019.
That would be a political disaster for Tony Newman's Labour group at the Town Hall, who will be expected to contest the May 2018 local elections on their record of "delivery" – so much so that they've recently spent thousands of pounds of public money redesigning the council's logos and letterheadings to include the line, "Delivering for Croydon", apparently used without irony.
The closure for the long-overdue refurbishment is already a disaster for the 150-or-so employees who were made redundant when the Fairfield Halls, which includes the Arnhem Gallery and Ashcroft Theatre, went "dark" in July on a council promise that the venues would re-open, fit for the 21st century, within two years.
Croydon's premier arts and entertainments centre would be "better than the South Bank", boasted the over-excited and unrealistic Newman when announcing the closure plans.
But a report to the council cabinet last week contained the first admission that the Fairfield Halls works are not proceeding to the tight schedule.
In an eight-page update delivered in the names of cabinet members Alison Butler and Timothy Godfrey and with no less than three "lead officers" at executive drector responsible – council CEO Jo Negrini, Paula Murray, the council's "creative director", and Colm Lacey, the director of development – the report contained a single line of text, buried deep towards the end of the paperwork:
"The indicative programme is as follows… Opening by end of 2018".
A planning application is yet to be submitted to the council for approval, although with Councillor Butler's husband, Paul Scott, as the chair of that committee, that would seem likely to be a formality. And, following a review by the Theatres' Trust, there have been some significant changes to the refurbishment scheme having already, such as scrapping plans for two large lorry lifts at the back of house, largely on grounds of expense.
But there's a growing possibility that even the slightest of further delays will mean that the Fairfield Halls risks missing its 2018 pantomime season – traditionally one of the biggest money-spinners for the venue.
That in itself could be a serious blow for the theatre operators which are bidding for the contract to run the venue, a process which was only started a few weeks ago and which is expected to be completed – according to the cabinet report – next May.
Despite the cabinet report confirming the delay to the building works, the scheme's dedicated website, meanwhile, continues to claim that the project is "on track".
But then, Croydon Council's notion of "on time" and "on budget" – Westfield? Bernard Weatherill House? – is clearly some way removed from the real world.
David Wickens, a former engineer at Croydon Council with a career spent overseeing major construction and infrastructure projects, is more wary about the Fairfield Halls meeting its tight timetable.
Wickens told Inside Croydon that the council report's "opening by end of 2018" could mean "no earlier than December 2018". He is concerned that a project that has managed to slip by six months on its planned delivery date, having only started five months ago, could be further delayed yet.
"When the council considered options for refurbishing Fairfield there were two main options," Wickens said. "The selected option was a full closure and a two-year refurbishment. This was the cheapest option but did mean redundancies of all the Fairfield staff. The alternative of a phased development and retention of staff was dismissed.
"I now see that within five-months of starting the two-year full closure has probably become a two-and-a-half-year full closure. That is a 25 per cent increase which no doubt has cost implications.
"This must call into question the approved business case and the redundancies.
"Let's hope that the reopening is not further delayed but I read elsewhere in the report that detailed design and contracts are some way off. In fact, the report says that the main refurbishment contractor will not start until May 2017, so the prospects of them finishing such major work before the end of 2018 must already be questionable."
Read the council cabinet's update report on the Fairfield Halls here
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Team Sonic Racing™ (Xbox Game EU)
Are you ready to have the race of your life with Sonic and his friends? Try out the new Team Sonic Racing on Xbox One and see how fast Sonic really is. With more than 15 playable characters, you can literally spend hundreds of hours racing and customizing your vehicles without even noticing how much time has passed.
Is standard racing the only option? Not by a long shot. Team Sonic Racing comes with a number of game modes including multiple single-player and multiplayer modes. You can go online, and enjoy the game with up to 11 other people. Also, you can play with 3 more people on the same console, with the 4-player split-screen mode. Offline, you can play the team Adventure mode.
The latter allows you to join forces with your friends and play as a team. You can combine your powers, abilities, and scores to win the Team Grand Prix. Not sure you can win the race you're in? Simply use your powers to wreak havoc on other players to help your teammates win the race and score additional points for your team.
Out of 15 different playable characters, there are 3 specific character types you can choose:
- Fast characters
- Technique-based characters
- Power-reliant characters
Not only can you customize the racing vehicle of your character but you can also alter their look to make them ready for the race both functionally and aesthetically. Use the customization options to race the way you want.


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As part of my job as a web developer, I spend an amount of time doing UI prototypes to show the client. It's a pain in the behind but sometimes it has to be done.
I've seen Shuttleworth (and the design team) pump out images like this:
That's made by something called Balsamiq Mockups... Something that balances on top of Adobe Air (yack!) and costs $79.
I've tried it but it kept falling over. I think it had something to do with Air not the app itself. My point is if I'm paying out for something, I want it to be native.


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Editor's Note – The height of hypocrisy is on full display by the Obama White House as tours are closed, FAA personnel and towers are cut, Blue Angels training is postponed, soldier tuition assistance is cut, and the list just keeps getting longer, all cited as cuts due to 'sequestration', yet many departments are hiring.
Not only that, but so much waste, duplicity, fraud, and abuse still goes on, despite Obama's pledge to go line by line over the budget to cut such egregious spending. But, "we have to keep releasing illegal aliens…!"
Government Advertises for Nearly 2,600 New Jobs Since Sequestration
This includes 107 new positions at the Department of Homeland Security, which has freed illegal immigrants citing budgetary constraints.
By Bridget Johnson – PJ Media
With Office of Management and Budget fact sheets in hand, President Obama warned of dire cutbacks and consequences should sequestration go into effect March 1. The cuts happened, White House tours have been halted, and the administration swears it's not overreacting to the bare-bones budget directive.
But in the days since the hammer of sequestration fell, the federal government is hiring anew. A search tonight of the USA Jobs federal employment website, filtered to positions in the United States and posted over the past 10 days, yielded 2,596 results.
This includes 107 positions at the Department of Homeland Security, which has claimed cutbacks have resulted in everything from a more taxing security line at airports to the need to free illegal immigrant detainees.
Jobs included transportation security officers in rural areas, a library technician in Baltimore, a recreational boating safety specialist in Cleveland, natural hazards program specialists in Denton, Texas, and various program analyst positions in the D.C. area. Various six-figure supervisory jobs are also open.
One hundred and fifteen jobs have been posted since sequestration began for the Agriculture Department, which warned of Americans falling ill from tainted food due to short staffing should sequestration go into effect.
Jobs posted included soil technicians, a recreation forestry technician in Sedona, Ariz., a dairy grader in Winnsboro, Texas, an archaeologist in McCall, Idaho, and a social science analyst.
The highest number of job postings since sequestration went into effect is at the Department of Veterans Affairs, with 909 new openings at the time of publication. The OMB painted a grim picture of tens of thousands of homeless vets being returned to the streets due to the budget cuts.
As the OMB warned Indian tribes would lose nearly $130 million in funding from the Interior Department, 115 new jobs have been posted in the sequestration era including multiple park guides to stock up for the summer, a museum aide, plant technicians, and more.
And while the White House warned of hundreds of furloughed federal prosecutors and a thousand fewer criminal cases being brought to court each year, the Justice Department has 46 new job postings including a public affairs specialist for the U.S. Attorneys, a law librarian, a trial attorney, and a deputy chief for the civil rights division.
New job postings at random agencies include a six-figure IT specialist at the Railroad Retirement Board, an exhibition aid for the National Gallery of Art, an Albanian-language broadcaster, and a space-assignment technician at the National Archives.
The office of the president is advertising for a management analyst, with a salary of $51,630 to $97,333 per year, to provide "assistance, research, advice and consultation on a full scope of administrative, managerial and financial projects in support of the Office of Administration." Relocation assistance is not included.
If anyone does want to complain about sequestration job losses, though, the Office of Personnel Management is hiring a customer service specialist for its call center.
Last week, Sen. Tom Coburn (R-Okla.) wrote to Acting OMB Director Jeffrey Zients, noting that many nonessential federal job postings were still going up despite pressure on the office to warn agencies that hiring activity should be scrutinized in the face of sequestration.
On the first business day after sequestration, 606 new jobs were posted on the USA Jobs site.
"While some of these positions may be essential to the mission of the agency, others plainly are not," Coburn wrote. "…According to OMB, the average annual salary for a government employee is around $76,000. This means that the average new hire equates to a one week furlough for 52 current government employees."
Jobs found by Coburn on March 4 and highlighted in the letter to Zients included 23 openings that included "recreation" in the title and a historian for the Federal Energy Regulatory Commission.
"While the Air Force may need leadership for its museums and history programs, and the USDA may need to keep its literature in order, those needs should take a back seat to the dire threat to public health and safety that some have claimed will result from sequestration," Coburn wrote. "Canceling the opening for the librarian position at USDA could offset one week of furloughs for as many as 104 to 156 food inspectors."


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Monday, July 12, 2010
SAN DIEGO WARES pt. II BOOTH 4800
I'm pleased to offer another exclusive small run item for San Diego this year: A set of 8 lobby cards, custom printed on high quality fine art paper and delivered in a film canister. These are incredibly small run, but offered at two sizes:
8 prints at approximately 4" x 5.25"
delivered in a hand-marked canister Approximately 7" in diameter
edition of 10
Plus an additional large size print of one of the cards (on 13"x 19" paper)
8 prints at approximately 3" x 4"
delivered in a hand-marked canister Approximately 5" in diameter
edition of 10
Please e-mail me at crazymorse*at*sbcglobal*dot*net if you'd like to reserve one of these. Available first at Comic Con. Any remaining stock will become available the week after the con right here on the blog.
Commissions will be done in full color this year on cold press Aquareller Arches watercolor paper. These will be offered at $150, an subject matter. Please bring reference if you want something crazy! Prints of other popular paintings will also be available in a small range of sizes. Please drop me a line if there's an image you'd really like, and I'll make sure it's there for you.
Posted by Scott Morse at 2:00 PM
1 comment:
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Media circus misses the point about child poverty
At his most partisan, documentary maker Bryan Bruce congratulates Sweden on its treatment of children.
The recent media circus over whether NZ On Air should scold problem child TV3 for their so-called political bias was a smokescreen, which largely missed the point, and was over as quickly as it started.
Of course TV3 is politically biased, it is a privately owned television network, but in this case they showed uncommon objectivity. It's amazing the documentary Inside Child Poverty by Bryan Bruce on New Zealand's child poverty problem was aired at all. He must have been very persistent.
So, some emails were leaked, and suddenly journalists (for want of a better word) start debating whether we need legislation to ban programming that criticises the government at election time. Yes, you heard right. Having gone through the motions of seeking legal advice after the fact, TV3 has been absolved. As if anyone expected anything else.
So many things are wrong with this picture; first off, the documentary doesn't take sides – it criticises both National and Labour-lead governments, both of which have stood idly by and let the problem continue, obfuscating and making excuses. At his most partisan, documentary maker Bryan Bruce congratulates Sweden on its treatment of children as precious and vulnerable members of society that need nurturing and protecting. He then urges all of New Zealand's political parties to work together to solve the problem. Tut tut.
Secondly, if you can't show programming that criticises the government at election time, when can you show it? Thirdly, if you can't have meaningful debate and cross-examination of those in power at election time, what can you have instead? Staged photo ops? Pre-masticated government press releases posing as reportage? Mind-numbing gossip sessions about Phil Goff 's hair dye and John Key's rugby attendance? 'Inside Child Poverty' was about the only thing of any substance to get traction on the airwaves coming up to the election.
By overflowing with drivel, New Zealand's mass media allows itself to be seen as harmlessly pappy infotainment. The truth is more sinister – by padding out pre-election airtime with rugby, celebrity scandals, sugar-coated assessments of the economy in geekspeak, and a storm in an Epsom teacup, the vast majority of New Zealand's mainstream media completely failed to do its job. To name a few examples of gross misconduct, they avoided doing their homework to expose empty promises made, such as John Key's explicit promise before he became prime minister, that he would not raise GST, only to do just that in his first term in government. They failed to question the National Party's misrepresentation that the Labour government spent irresponsibly on public services leaving behind them a budget deficit which National had to clean up*; they dodged having to ask John Key how he justifies giving himself and his cronies a large tax break while doing nothing about the eminently preventable problem of children living in damp, cramped houses and going to school hungry.
Now, having at last unearthed the truth about how we are treating our weakest citizens, we have the next petty distraction: the pretend obsession with being 'fair and balanced', as if a guilt-free news broadcaster would need to constantly reiterate how 'fair', 'balanced' and 'neutral' they are (just look at Fox News). It's like a priest going around insisting that God exists: you wonder who he's trying to convince. 'Balance' would be showing how the children of the richest New Zealanders live compared to those in poverty.
Documentaries that look at the ills of society are acceptable as long as they don't dig too deep, don't draw any conclusions about the causes, and above all, don't suggest any solutions, the latter being a cardinal sin of journalism.
Perhaps this has been a cynical publicity stunt on the part of TV3, in cahoots with NZOA, to make out that it has lefty tendencies that need to be curbed. Or perhaps they are just so out of touch with the New Zealand public that they all need to be sacked. Chair of NZ On Air, Neil Walter, doesn't "believe the New Zealand public would expect or want to see their funding put into a politically-charged scenario like that... We are barred by legislation from seeking to influence editorial content... but in this case we felt that we had been dropped in it... just three days out from voting..."
Actually, it was four days out from the election, but we can't expect or want Neil Walter to get his facts straight. Here are some facts: 385,900 New Zealanders watched the documentary when it premiered last November, according to Neilsen TAM, and it was the most watched programme in its timeslot. Hmmm... clearly New Zealanders aren't interested in watching 'politically-charged' documentaries. Over 14,000 more people watched it online in the next two days.
-Sian R., SA
*Labour more or less balanced the budget. National sent the country further into debt to cover the tax cuts to the rich, which they are now trying to pay for by selling bits of our country out from under us.


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Real Estate Investing: Why Cash Flow is King
As real estate values rise nationwide and many properties listed for sale are being fought over by investors and home buyers, it seems that, once again, investment property buyers are paying outrageous prices for properties. Anyone recall this phenomenon in 2004, 2005 and 2006?
An "outrageous price" is one that is way too high considering the cash flows the rental property can generate. These negative cash flow properties are rarely profitable investments, compared with other investment options a buyer could have chosen.
Experienced real estate investors only buy properties that are cash-flow positive — based on conservative estimates — and skip those pesky negative cash flow deals. Note that those negative cash flow properties are typically the fancy prize properties in town; you know, the location, location, location properties.
Penciling out a deal
The main reason investors keep paying these high prices is because 95 percent of them acquire properties without doing any financial analysis to determine whether the property will actually produce decent investment returns. Instead, they hope that a property will go up in value, they'll sell it and make a bundle. Unfortunately, that scenario rarely happens.
As an example, let's say an investor buys a $125,000 house by investing cash equity of $40,000 (25 percent down payment plus closing costs and rehabilitation costs) that generates rental income of $1,200 per month. The mortgage plus other operating expenses total $1,015 per month. So the rent less all the expenses leaves $185 of positive monthly income, or $2,220 per year. If we divide this $2,220 annual cash flow by the $40,000 initial cash investment, it calculates to a cash-on-cash return of 5.55 percent — a pretty fair deal on a decent real estate investment.
Additional perks
Only about half of the properties in a general marketplace would generate positive cash flows and a decent, actual return such as 5.55 percent. In actuality, real estate investing is much more complicated than just penciling out your cash-on-cash return, but that analysis is a good start.
And with that nice positive cash flow, you also will get some extra return yield as a result of the amortization of your mortgage. Plus you probably will get some tax benefits and possibly some appreciation in value too.
Cash flow is king, and if you buy positive cash flow properties, you will feel like royalty each month as your bank account balance builds up and you earn wealth over the years!
Read More From Zillow:
- 3 Things That Make the Best Real Estate Investment
- The 6 Worst Types of Real Estate Investments
- Are You Ready to Be a Landlord?
Leonard Baron, MBA, is America's Real Estate Professor®. His unbiased, neutral and inexpensive "Real Estate Ownership, Investment and Due Diligence 101" textbook teaches real estate owners how to make smart and safe purchase decisions.
Note: The views and opinions expressed in this article are those of the author and do not necessarily reflect the opinion or position of Zillow.