Unformatted text preview: the identity of Alice and d is arbitrary data. The data may be encrypted with Alice’s public key, EA, for security. RA is the random number Alice generated in step (1). (11) Bob sends DB(M’) to Alice. (12) Alice uses EB to decrypt DB(M’). This verifies both Bob’s signature and the integrity of the signed information. (13) Alice checks the IA in M’ for accuracy. (14) Alice checks the TB in M’ and confirms that the message is current. (15) As an option, Alice can check the RB in M’ to ensure the message is not an old one being replayed. The three-way protocol accomplishes the same thing as the two-way protocol, but without timestamps. Steps (1) through (15) are identical to the two-way protocol, with TA = TB = 0. (16) Alice checks the received version of RA against the RA she sent to Bob in step (3). (17) Alice sends DA(RB) to Bob. (18) Bob uses EA to decrypt DA(RB). This verifies both Alice’s signature and the integrity of the signed information. (19) Bob checks the received version of RB against the RB he sent to Alice in step (10). 24.10 Privacy-Enhanced Mail (PEM)
PEM is the Internet Privacy-Enhanced Mail standard, adopted by the Internet Architecture Board (IAB) to provide secure electronic mail over the Internet. It was initially designed by the Internet Research Task Force (IRTF) Privacy and Security Research Group (PSRG), and then handed over to the Internet Engineering Task Force (IETF) PEM Working Group. The PEM protocols provide for encryption, authentication, message integrity, and key management. The complete PEM protocols were initially detailed in a series of RFCs (Requests for Comment) in  and then revised in . The third iteration of the protocols [979, 827, 980] is summarized in [177, 178]. The protocols were modified and improved, and the final protocols are detailed in another series of RFCs [981, 825, 76, 802]. Another paper by Matthew Bishop  details the changes. Reports of attempts to implement PEM include [602, 1505, 1522, 74, 351, 1366, 1367]. See also . PEM is an inclusive standard. The PEM procedures and protocols are intended to be compatible with a wide range of key-management approaches, including both symmetric and public-key schemes to encrypt data-encrypting keys. Symmetric cryptography is used for message-text encryption. Cryptographic hash algorithms are used for message integrity. Other documents support key-management mechanisms using public-key certificates; algorithms, modes...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips