6.2 Cryptography overview 6.2.1 Modern cryptography From the early beginning of human history, when two people were communicating with each  other, the demand always existed to keep certain messages secret so that a third person  cannot understand what the sender is telling to the receiver.  Also, it is necessary to ensure that a message cannot be corrupted, while ensuring that the  sender and the receiver really are the persons who they claim to be. Over time, several  methods were used to achieve these objectives, with more or less success. Many procedures  and algorithms for encrypting and decrypting data were developed that are increasingly  complicated and time-consuming. With the development of computing technology, the encryption and decryption algorithms can  be performed by computers, which enables the use of complicated mathematical algorithms.  Most of these algorithms are based on the prime factorization of large numbers.  Modern cryptography involves the following purposes for protecting information: GLYPH<SM590000> Data protection GLYPH<SM590000> Authentication (identity validation) GLYPH<SM590000> Integrity GLYPH<SM590000> Non-repudiation The protection of data usually is the main concept that is associated with cryptography.  Only authorized persons should be able to read the message or get information about it.  Data is encrypted by using a known algorithm and secret keys, such that the intended  party can de-scramble the data, but an interloper cannot. This idea is also referred to as  confidentiality . This process decides whether the communication partners are who they claim to be,  which can be done by using certificates and signatures. It must be possible to clearly  identify the owner of the data or the sender and the receiver of the message. The verification of data ensures that what was received is identical to what was sent. It  must be proven that the data is complete and was not altered during the moment it was  transmitted (by the sender) and the moment it was received (by the receiver). It must be impossible for the owner of the data or the sender of the message to deny  authorship. Non-repudiation ensures that both sides of a communication know that the  other side agreed to what was exchanged, and not someone else. This specification  implies a legal liability and contractual obligation, which is the same as a signature on a  contract. These goals should all be possible without unacceptable overhead to the communication. The  goal is to keep the system secure, manageable, and productive. The basic method data protection is to encrypt and decrypt it, while for authentication,  integrity and non-repudiation, hash algorithms, message authentication codes (MACs), digital  signatures, and certificates are used.  Chapter 6. Cryptographic features  209