Public Key Cryptography is a concept that solves many problems related to key distribution. This concept was introduced in 1975 by Whitfield Diffie and Martin Hellman. (There is now evidence available that the British Secret Service (BSS) invented it a few years before Diffie and Hellman, but kept it as a military secret. Anyway, Public key cryptography is an asymmetric method that uses a pair of keys for encryption: a public key, which is used to encrypt data, and its corresponding private key, or secret key, that is used for decryption.

The public key is available to the whole world while the private key is known only by the user. To encrypt data so that only the user can read it, another user would require the first user’s public key. The two users do not have to know each other in person for this to happen. It is not feasible computationally to glean the private key from the public key. Anyone who has a public key can encrypt info but cannot decrypt it. Only the person who has the corresponding private key can decrypt the info.

A big advantage of public key cryptography is that it provides a method for the employment of digital signatures, which enables the recipient of the information to verify the credibility of the information’s origins, and also to check whether or the information is intact. So, public key digital signatures provide a method for authentication as well as data integrity. A digital signature also provides non-repudiation.

The basic manner in which Pretty Good Privacy (PGP) – a computer program for data encryption and decryption) – creates digital signatures is explained in the following. Rather than performing encryption using a public key, PGP does encryption with a private key. If the information can be decrypted with the public key of a user, then it must have originated with said user.

PGP, in order to sign keys, uses a ‘web of trust’. In this web people sign each other’s keys as valid when they know the identity of the key possessors being trustworthy . This is effective because if a key is signed by a certain number of ‘trusted’ users, it makes the ownership of the key and identity of the owner trust worthy. Incorrect authorization can result in unauthorized people gaining access among other disadvantages.

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Public Key Cryptography by PGP
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