Cryptographic Protocols and Standards

Cryptography works on many levels. On one level you have algorithms, such as block ciphers and public key cryptosystems. Building upon these you obtain protocols, and building upon protocols you find applications (or other protocols).

It is not sufficient to study the security of the underlying algorithms alone, as a weakness on a higher-level protocol (or application) can render the application insecure regardless of how good the underlying cryptographic algorithms are. A simple example is a protocol that leaks information about the key being used to encrypt the communication channel. Irrespective of how good the encryption algorithms are, they are rendered insecure if the overlying protocol reveals information on the keys used in encryption.

The analysis of protocols is often difficult because the applications that implement such protocols may lead to further problems. Thus a good protocol is not enough, you must also have a good and robust implementation.

In the following, several well-known protocols and standards are mentioned.

• Domain Name Server Security (DNSSEC).

  This is a protocol for secure distributed name services. It is currently available as an Internet Draft.

• Generic Security Services API (GSSAPI)

  GSSAPI provides an authentication, key exchange, and encryption interface to different cryptographic algorithms and systems. [RFC1508]

• Secure Socket Layer (SSL)

  SSL is one of the two protocols for secure WWW connections (the other is SHTTP). WWW security has become important as increasing amounts of sensitive information, such as credit card numbers, are being transmitted over the Internet.

  SSL was originally developed by Netscape as an open protocol standard. openssl.org contains some documents and provides an open source implementation.

• Secure Hypertext Transfer Protocol (SHTTP)

  This is another protocol for providing more security for WWW transactions. In many ways it is more flexible than SSL, but due to Netscape's original dominance in the marketplace SSL is in a very strong position. [RFC2660]

• E-Mail security and related services
  • OpenPGP is a standardization of what Phil Zimmermann's PGP already did for many years. But now that it is a standard, different implementations come into existence.
  • Secure-MIME (S/MIME) is an alternative for the OpenPGP standard maintained by the IETF working group S/MIME.

• Public Key Encryption Standards(PKCS)

  These standards are developed at RSA Data Security and define safe ways to use RSA. Some documents published by RSA Laboratories are available at their ftp site.

• IEEE P1363: Standard Specifications for Public-Key Cryptography

  A (upcoming) standard for public key cryptography. Consists of several public key algorithms for encryption and digital signatures. Has a very thorough annex that goes through all necessary implementation details. See more at their homepage.

• Publius Censor-Resistent Publishing Protocol

  This is a very advanced system allowing a group of authors and readers to share documents on a set of web servers so that (1) no author or reader has to reveal his/her identity, (2) documents are certified to come from a certain (pseudonymous) author, (3) documents cannot be removed or modified (censored) unless a large amount of the involved web servers are compromised. Technical reports, software and links to related projects can be found on the homepage.

• SSH2 Protocol

  SSH2 is developed by the IETF working group SecSH. This protocol is versatile for the needs of the internet, and is currently used in the SSH2 software. The protocol is used to secure terminal sessions and arbitrary TCP connections. The SSH2 protocol is based on its predecessor SSH1 developed by Tatu Ylönen. Protocol specifications (drafts) can be found from the IETF.

• IPSec

  While all the above protocols operate on the application layer of the internet, allowing particular programs to communicate on a secure channel in an inherently insecure network, IPSec attempts to make the internet secure in its essence, the internet protocol (IP). A list of RFC's and a full-scale implementation can be found at the SSH site.