This preview shows page 1. Sign up to view the full content.
Unformatted text preview: neman’s Methods
This MAC is also called a quadratic congruential manipulation detection code (QCMDC) [792, 789]. First, divide the message into m- bit blocks. Then: H0 = IH, where IH is the secret key Hi = (Hi- 1 + Mi)2 mod p, where p is a prime less than 2m - 1 and + denotes integer addition Jueneman suggests n = 16 and p = 231 - 1. In  he also suggests that an additional key be used as H1, with the actual message starting at H2. Because of a variety of birthday-type attacks discovered in conjunction with Don Coppersmith, Jueneman suggested computing the QCMDC four times, using the result of one iteration as the IV for the next iteration, and then concatenating the results to obtain a 128-bit hash value . This was further strengthened by doing the four iterations in parallel and cross-linking them [790, 791]. This scheme was broken by Coppersmith . Another variant [432, 434] replaced the addition operation with an XOR and used message blocks significantly smaller than p. H0 was also set, making it a keyless one-way hash function. After this scheme was attacked , it was strengthened as part of the European Open Shop Information-TeleTrust project , quoted in CCITT X.509 , and adopted in ISO 10118 [764, 765]. Unfortunately, Coppersmith has broken this scheme as well . There has been some research using exponents other than 2 , but none of it has been promising. RIPE-MAC
RIPE-MAC was invented by Bart Preneel  and adopted by the RIPE project  (see Section 18.8). It is based on ISO 9797 , and uses DES as a block encryption function. RIPE-MAC has two flavors: one using normal DES, called RIPE-MAC1, and another using triple-DES for even greater security, called RIPE-MAC3. RIPE-MAC1 uses one DES encryption per 64-bit message block; RIPE-MAC3 uses three. The algorithm consists of three parts. First, the message is expanded to a length that is a multiple of 64 bits. Next, the expanded message is divided up into 64-bit blocks....
View Full Document
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