Q8: Explain DES algorithm.
Ans Digital Signature Algorithm
DSA was developed as part of the Digital Signature Standard (DSS). (A more detailed discussion of DSS and DSA is provided later in this chapter.) Unlike the Diffie-Hellman and RSA algorithms, DSA is not used for encryption but for digital signatures. A Slight Digression For many years it was believed that Whitfield Diffie and Martin Hellman were the first to conceive of asymmetric cryptography and that Ron Rivest, Adi Shamir, and Len Adelman were the first to develop the RSA algorithm. However, it is now claimed that neither collaborative was the first and that the concept of asymmetric cryptography, the Diffie-Hellman algorithm, and the RSA algorithm were all discovered years earlier in England by the Government Communications Headquarters (GCHQ), which is the British equivalent of the NSA. The GCHQ claims that it conceived ofthe concept years before anyone else but never released information on the work for national security reasons. Message Integrity To attain a high level of confidence in the integrity of a message or data, a process must be put in place to prevent or detectalteration during transit. One technique employed is called a hash function. A hash function takes a message of any length and computes a product value of fixed length. The product is referred to as a "hash value." The length of the original message does not alter the length ofthe hash value. Hash functions are used to ensure the integrity of a message or file. Using the actual message or file, a hash function computes a hash value, which is a cryptographic checksum of the message. This checksum can be thought of as a fingerprint for that message. The hash value can be used to determine if the message or file has been altered since the value was originally computed.<