Red Hat DIRECTORY SERVER 8.1 - 11-01-2010 Manual de usuario descargar pdf (Pagina 6)

A digital signature is generated by an algorithm that uses a hash function in

conjunction with a key. A hash function is a function that takes in input a

message of any length, and outputs a string of fixed small length called digest

which is a distillate of the message fed in input. Notable features of hash

functions include that is practically impossible to derive the input from the

output, and that changing just one bit of the input results in a completely

different output.

Hence Bob writes the message, generates the digital signature for the message

using a predetermined hash function and his private key, appends the signature

to the message, and sends to Alice the whole lot. Alice receives the message

and verifies the signature using the same hash function and Bob's public key.

If the signature is valid, then the sender is authenticated, because only the

owner of the private key, Bob, could have signed the message. This

guarantees also the integrity of the message, because had the message been

altered in transit, it would resolve to a different digest and the signature would

not match.

Public key cryptography was firstly discovered by James Ellis, Clifford Cocks

and Malcolm Williamson of the British Government Communication

Headquarters in 1975, but the discovery was filed as classified information and

never divulged. The following year researchers Whitfield Diffie, Martin Hellman

and Ralph Merkle independently made the same discovery and published it on

a paper. One year later Ronald Rivest, Adi Shamir and Leonard Adleman

provided the first practical implementation of a public key cryptography

algorithm by developing the RSA cipher.

Then in 1991 Phil Zimmermann, a free speech activist and anti-nuclear pacifist,

developed Pretty Good Privacy (PGP), the first software available to the general

public that utilized RSA for email encryption and signing. Zimmermann, after

having asked a friend to post the program on the worldwide Usenet, found

himself prosecuted by the government and was even charged by the FBI for

illegal weapon export. The charges were eventually dropped, and Zimmermann

later founded PGP Inc., now acquired by PGP Corporation.

In 1997 PGP Inc. submitted a standardization proposal to the Internet

Engineering Task Force. The standard was called OpenPGP and defined in

1998 in the IETF document RFC 2440. The latest version of the OpenPGP

standard is described in RFC 4880, published in 2007.

PGP is now a famous commercial product for communication security and

privacy in corporate, business and home environment, and is available at

http://www.pgp.com and http://www.pgpi.org .

Nowadays there are many OpenPGP-compliant products: the most widespread

is probably GnuPG (GNU Privacy Guard, or GPG for short) which was

developed in 1999 by Werner Koch. The GnuPG Project is hosted at

http://www.gnupg.org .

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Red Hat DIRECTORY SERVER 8.1 - 11-01-2010 Manual de usuario Pagina 6