Unformatted text preview: it to Trent. (3) Trent verifies the outside signature and confirms the identifying information. He adds a timestamp to Alice’s signed message and the identifying information. Then he signs it all and sends it to both Alice and Bob. (4) Bob verifies Trent’s signature, the identifying information, and Alice’s signature. (5) Alice verifies the message Trent sent to Bob. If she did not originate the message, she speaks up quickly. Another scheme uses Trent after the fact . After receiving a signed message, Bob can send a copy to Trent for verification. Trent can attest to the validity of Alice’s signature. Applications of Digital Signatures
One of the earliest proposed applications of digital signatures was to facilitate the verification of nuclear test ban treaties [1454,1467]. The United States and the Soviet Union (anyone remember the Soviet Union?) permitted each other to put seismometers on the other’s soil to monitor nuclear tests. The problem was that each country needed to assure itself that the host nation was not tampering with the data from the monitoring nation’s seismometers. Simultaneously, the host nation needed to assure itself that the monitor was sending only the specific information needed for monitoring. Conventional authentication techniques can solve the first problem, but only digital signatures can solve both problems. The host nation can read, but not alter, data from the seismometer, and the monitoring nation knows that the data has not been tampered with. 2.7 Digital Signatures with Encryption
By combining digital signatures with public-key cryptography, we develop a protocol that combines the security of encryption with the authenticity of digital signatures. Think of a letter from your mother: The signature provides proof of authorship and the envelope provides privacy. (1) Alice signs the message with her private key. SA(M) (2) Alice encrypts the signed message with Bob’s public key and sends it to Bob. EB(SA(M)) (3) Bob decrypts the message with his private key. DB(EB(SA(M))) = SA(M) (4) Bo...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.
- Fall '10