Collision-resistant hash function using determ. block cipher
{"Image DocumentName": "Collision-resistant hash function using determ. block cipher", "Image ImageDescription": "! nearly no, but well analyzed. efficient any cryptographically strong. initial value is fixed! (else trivial collisions: intermediate blocks and truncated plaintexts) last block contains length in bit. differently long. birthday paradox. after 2b/2 tests collision. b. encryption. plaintext block n. memory for intermediate block n-1. last block. \uf0b7 organisational things: lectures / excercies side by side\u2026 something not in wide use: how to construct hash functions: today other ways of construction (md5, sha) now: using block cipher (we had it for encryption/authentication) it\u2018s from a book not from my brain. what do we want to have: efficent! (engienieering approach.. \uf04a ): not too many calls of the block cipher; not to much around: so not more worse one the block cipher\u2026 cryptohgraphical strong! \uf0e0 underlying block cipher could be broken. should work for  any  block cipher. dream! what do we get: very, very uncoming use of block cipher! only encryption \uf0e0 but look for the key! no surprise: hash functions do not have keys\u2026 block length \uf0e8 key length (not DES: 56! bit) input: previous value. last block = hash value. problem: multiply of key length\u2026.so padding is necessary! output: block length \uf0e0 DES: 64 bits \uf0e0 today much to short; why? 2^64 is not really weak\u2026 reason: birthday paradox \uf0e0 [explain reason for naming it \u201ebirthday paradox ] \uf0e0 how many do we need: 23 (57: 99%) \uf0e0 wikipedia. birthday = kollison. large block cipher\u2026 difference: key legnth; block length. initial value has to be fixed! length field! final result: efficent! not cryptographical strong but well analyzed; nearly: key length ~ block length.", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}