What are the services of PGP?

PGP includes the following services which are as follows −

Authentication − The hash function used is SHA-1 which makes a 160 bit message digest. EP (DP) defines public encryption (decryption) and the algorithm used can be RSA or DSS.

The set of SHA-1 and RSA supports an effective digital signature scheme. Because of the strength of RSA the recipient is guaranteed that only the possessor of the connecting private key can make the signature. Because of the strength of SHA-1 the recipient is guaranteed that no one else can create a new message that connects the hash code and therefore the signature of the original message.

Confidentiality − It is a service supported by PGP is confidentiality which is provided by encrypting messages to be transmitted or to be saved locally as files. In some cases, the user has a best of CAST-128, IDEA or 3DES in 64 bit cipher feedback (CFB) mode. The symmetric key is used only once and is generated as a random number with the required number of bits. It is acquired along with the message and is encrypted using the recipient’s public key.

  • The sender creates a message and a random number to be used as a session key for this message only.

  • The message is encrypted utilizing CAST-128, IDEA or 3DES with the session key.

  • The session key is encrypted with RSA utilizing the recipient’s public key and is prepended to the message.

  • The receiver uses RSA with its private key to decrypt and restore the session key.

  • The session key can be used to decrypt the message.

Confidentiality and Authentication − The both services can be used for the same message. First, a signature is produced for the plaintext message and prepended to the message. Therefore the plaintext message plus signature is encrypted using CAST-128 (or IDEA or 3DES), and the session key is encrypted using RSA.

This sequence is desirable to the opposite encrypting the message and thus producing a signature of the encrypted message. It is usually more convenient to save a signature with a plaintext version of a message. Moreover, for the goals of third party verification, if the signature is implemented first, a third party need not be concerned with the symmetric key when testing the signature.

Compression − As a default, PGP restrict the message after using the signature but before encryption. This has the advantage of storing space both for e-mail transmission and for file storage.

E-mail compatibility − Some electronic mail systems only allows the use of blocks including ASCII text. When PGP is used, minimum part of the block to be transmitted is encrypted.

Segmentation − E-mail facilities are restricted to a maximum message length. For instance, some facilities accessible throughout the internet set a maximum length of 50,000 octets. Some message higher than that should be broken up into smaller segments, each of which is mailed independently.