To protect the integrity of the signature, PKI requires that the keys be created, conducted, and  saved in a secure manner, and often requires the services of a reliable certificate authority  (CA). Digital signature providers must meet PKI requirements for safe digital signing. Package signing is a security technology that IBM uses to certify that AIX development  created an OS-related package. After a package is signed, the system can detect any change  to the package content. The benefits of package signing are: Package signing is just one component of a complete security solution that works in concert  with other technologies, for example, AIX secure boot (2.2, “AIX Secure boot” on page 66)  and AIX TE (2.1, “AIX Trusted Execution” on  page 62). In the context of a comprehensive  security strategy it is also important to know about the limitations of package signing: GLYPH<SM590000> Ensure that the package content has not been altered since it was signed. AIX systems  can detect any form of changes to a package, whether it is intentional (by a malicious  attacker) or accidental (for example, when a file is corrupted). When a package signature  is intact, the AIX system is sure that the content is as the signer intended. GLYPH<SM590000> Identify packages as coming from a specific source. The package signature includes  cryptographic information that unambiguously points to a particular author (IBM AIX  development). This information is included in the certificates that are published by the AIX  package builder. GLYPH<SM590000> Determine whether a package is trustworthy for a specific purpose. Among other things,  an AIX package builder can use a digital signature to state that an updated version of a  product should be considered by the AIX system to be the same product as the previous  release version. GLYPH<SM590000> Package signing does not ensure that a package is free of security vulnerabilities. GLYPH<SM590000> Package signing does not ensure that a software program will not load unsafe or altered  code during execution. GLYPH<SM590000> No copy protection technology is provided because package signing does not in any way  hide or obscure the content of the signed package. 2.3.2 AIX package signing and digital signature catalog definition Seal Chapter 2. Security enhancements  71 Seal A seal is a collection of checksums or hashes of the various parts of a  package that is created by the package signing software. The package  seal is used at verification time to detect alterations. Digital signature The package signing software encrypts the seal by using the signer’s  identity to create a digital signature, which ensures the seal’s integrity. Sign requirements These requirements are the security policies and rules governing the  verification of the package signature. Some are inherent to the verifier  (depending on its goals). Others are specified by the signer and  sealed with the rest of the code (for example, version, release,  modification, and fix (VRMF) level designation, message-digest  algorithm, and keystore origin). The underlying AIX package signing program generates the seal by running different parts of  the source through a one-way hashing algorithm. This algorithm produces a series of digests,  or checksums, which are short strings of digits that are unique to a particular input block, but  that cannot be used to reconstruct the original input. Beginning with AIX 7.2 TL 4, AIX development delivers signed OS software packages in the  installp  format. The package signature consists of three parts: