| Popis: |
Cryptography is the only powerful tool for achieving high levels of information security in a computer networks environment. The ISO have proposed five security service groups including, confidentiality, authentication, data integrity, non-repudiation, and access control. Cryptography can support implementation of all these security services, by using various cryptographic techniques, which include among other things conventional secret key algorithms, public-key algorithms, authentication procedures, and different digital signature schemes. Hash functions, in cryptography, are used for digital signature applications and authentication procedures. It is advisable, for cryptographic reasons, to sign only hashed messages. A secure hash function must be a one-way and collision-free function. Cryptographic security of hash functions could be evaluated, so far, either by conducting detailed cryptanalysis, or by using computational complexity theory. Each of these methods has its own shortcomings. A new scheme for evaluating the cryptographic security of hash functions is proposed. The proposed scheme is simple, fast, and based on a solid mathematical model offered by Markov process. The proposed scheme is used to evaluate the cryptographic security of the Message Digest MD-4 algorithm. The results are in accordance with what was conjectured and published. |
