Digital Signatures

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Digital Signatures are a type of asymmetric cryptography or used to simulate the security properties of a handwritten signature on paper. Digital signature schemes normally give two algorithms, one for signing which involves the user's secret or private key, and one for verifying signatures which involves the user's public key. The output of the signature process is called the "digital signature."

There is confusion between the terms electronic signature and digital signature. Most, especially those with an information theory or cryptography background, use "digital signature" to refer to a digital signature protocol using cryptographic techniques, as is sometimes applied to an 'electronic document'. Many, however, use the terms interchangeably, leading to considerable confusion as cryptographic signature techniques are very different, whatever the term used, than other electronic signatures and have extremely different security properties. Since it is the security properties which are of interest in signatures of all kinds, this is a very significant distinction. Digital signature is properly a subset of electronic signature.

History

The history of cryptography begins thousands of years ago. Until recent decades, it has been the story of what might be called classic cryptography — that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids. In the early 20th century, the invention of complex mechanical and electromechanical machines, such as the Enigma rotor machine, provided more sophisticated and efficient means of encryption; and the subsequent introduction of electronics and computing has allowed elaborate schemes of still greater complexity, most of which are entirely unsuited to pen and paper.

The first invention of asymmetric key algorithms was by James H. Ellis, Clifford Cocks, and Malcolm Williamson at GCHQ in the UK in the early 1970s; these inventions were what later became known as Diffie-Hellman key exchange, and a special case of RSA. The GCHQ cryptographers referred to the technique as "non-secret encryption". These inventions were not publicly disclosed at the time, and the fact that they had been developed was kept secret until 1997.

The first widely marketed software package to offer digital signature was Lotus Notes 1.0, released in 1989, which used the RSA algorithm.

Cryptography

Cryptography is the practice and study of hiding information. In modern times, cryptography is considered to be a branch of both mathematics and computer science, and is affiliated closely with information theory, computer security, and engineering. Cryptography is used in applications present in technologically advanced societies; examples include the security of ATM cards, computer passwords, and electronic commerce, which all depend on cryptography.

Asymmetric key

Asymmetric cryptography, is a form of cryptography in which a user has a pair of cryptographic keys—a public key and a private key. The private key is kept secret, while the public key may be widely distributed. The keys are related mathematically, but the private key cannot be practically derived from the public key. A message encrypted with the public key can be decrypted only with the corresponding private key.

Symmetric key

Symmetric cryptography refers to encryption methods in which both the sender and receiver share the same key (or, less commonly, in which their keys are different, but related in an easily computable way). This was the only kind of encryption publicly known until June 1976.^[1] Symmetric authentication keys are used with symmetric key algorithms to provide assurance of the integrity and source of messages, communication sessions, or stored data.