Lecture "On safety and security of information systems: Cryptographic hash funtionns" provide students with knowledge about: Hash function; Applications of cryptographic hash functions; Simple hash functions; Requirements and security; . Please refer to the detailed content of the lecture! | CRYPTOGRAPHIC HASH FUNTIONS Contents 1 Hash function 2 Applications of Cryptographic Hash Functions 3 Simple Hash Functions 4 Requirements and Security 5 Secure Hash Algorithm SHA 1. Hash function A hash function maps a variable-length message into a fixed-length hash value or message digest h H M 1. Cryptographic hash function. A cryptographic hash function is an algorithm for which it is computationally infeasible to find either a data object that maps to a pre- specified hash result or two data objects that map to the same hash result 2. Applications Of Cryptographic Hash Functions Message Authentication Digital signature Message Authentication Message authentication is a mechanism or service used to verify the integrity of a message. Message authentication assures that data received are exactly as sent Message Authentication Digital signature The hash value of a message is encrypted with a user s private key. Anyone who knows the user s public key can verify the integrity of the message that is associated with the digital signature Other Applications Hash functions are commonly used to create a one-way password file Hash functions can be used for intrusion detection and virus detection 3. Simple Hash Functions Input message file etc. is viewed as a sequence of n-bit blocks One of the simplest hash functions is the bit-by-bit exclusive-OR XOR of every block. This can be expressed as 4. Requirements And Security 5. Secure Hash Algorithm SHA SHA-512 SHA-512 Step 1 Append padding bits The padding consists of a single 1 bit followed by the necessary number of 0 bits Step 2 Append length A block of 128 bits is appended to the message. This block is treated as an unsigned 128-bit integer and contains the length of the original message before the padding . SHA-512 Step 3 Initialize hash buffer A 512-bit buffer is used to hold intermediate and final results of the hash function. The buffer can be represented as eight 64-bit registers a b c d e f g h . These registers .
