User guide

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communications channel. This key can then be used to encrypt subsequent communications using a

symmetric key cipher.

A.2.1.1. Diffie-Hellman History

The scheme was first published by Whitfield Diffie and Martin Hellman in 1976, although it later

emerged that it had been separately invented a few years earlier within GCHQ, the British signals

intelligence agency, by Malcolm J. Williamson but was kept classified. In 2002, Hellman suggested the

algorithm be called Diffie–Hellman–Merkle key exchange in recognition of Ralph Merkle's contribution

to the invention of public-key cryptography (Hellman, 2002).

Although Diffie–Hellman key agreement itself is an anonymous (non-authenticated) key-agreement

protocol, it provides the basis for a variety of authenticated protocols, and is used to provide perfect

forward secrecy in Transport Layer Security's ephemeral modes (referred to as EDH or DHE

depending on the cipher suite).

U.S. Patent 4,200,770, now expired, describes the algorithm and credits Hellman, Diffie, and Merkle

as inventors.

A.2.2. RSA

In cryptography, RSA (which stands for Rivest, Shamir and Adleman who first publicly described it;

see below) is an algorithm for public-key cryptography. It is the first algorithm known to be suitable for

signing as well as encryption, and was one of the first great advances in public key cryptography. RSA

is widely used in electronic commerce protocols, and is believed to be secure given sufficiently long

keys and the use of up-to-date implementations.

A.2.3. DSA

DSA (Digital Signature Algorithm) is a standard for digital signatures, a United States federal

government standard for digital signatures. DSA is for signatures only and is not an encryption

algorithm.

A.2.4. SSL/TLS

Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic

protocols that provide security for communications over networks such as the Internet. TLS and SSL

encrypt the segments of network connections at the Transport Layer end-to-end.

Several versions of the protocols are in widespread use in applications like web browsing, electronic

mail, Internet faxing, instant messaging and voice-over-IP (VoIP).

A.2.5. Cramer-Shoup Cryptosystem

The Cramer–Shoup system is an asymmetric key encryption algorithm, and was the first efficient

scheme proven to be secure against adaptive chosen ciphertext attack using standard cryptographic

assumptions. Its security is based on the computational intractability (widely assumed, but not proved)

"Diffie-Hellman." Wikipedia. 14 November 2009 http://en.wikipedia.org/wiki/Diffie-Hellman

"DSA." Wikipedia. 24 February 2010 http://en.wikipedia.org/wiki/Digital_Signature_Algorithm

"TLS/SSl." Wikipedia. 24 February 2010 http://en.wikipedia.org/wiki/Transport_Layer_Security