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# Secure Hashing Techniques - Introduction

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Secure hashing what is it ? why do we need it ?
where do we use it ? A set of secure hashing techniques there pros and cons and their comparisons.

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### Secure Hashing Techniques - Introduction

1. 1. SECURE HASHING TECHNIQUES By UdhayyaGethan.M 311511205309
2. 2. SECURE HASHING • What ? • Why ? • How ?
3. 3. What is Hashing • A hash function is any algorithm that maps data of variable length of data to a fixed length. • The values returned by the hash functions are called as hash codes, hash sums, message digest or simply hashes. • Hashing mostly takes a string as an input and gives the output or the hashed values as a numerical value mostly as an hexadecimal number.
4. 4. What is so special about Secure Hashing • Hash values produced by some hash techniques can be re hashed. • That means we can get the original data from the hash values. • But hash values of secure hash techniques cant be rehashed. • That’s why it is called as one way hashing.
5. 5. Message Digest Functions: • Checksums  fingerprint of a message • If message changes, checksum will not match • Most checksums are good in detecting accidental changes made to a message • They are not designed to prevent an adversary from intentionally changing a message resulting a message with the same checksum • Message digests are designed to protect against this possibility
6. 6. One-Way Hash Functions: Example • M = “Elvis” • H(M) = (“E” + “L” + “V” + “I” + “S”) mod 26 • H(M) = (5 + 12 + 22 + 9 + 19) mod 26 • H(M) = 67 mod 26 • H(M) = 15
7. 7. Collision: Example • x = “Viva” • Y = “Vegas” • H(x) = H(y) = 2
8. 8. Criteria's for a hash function: • Given M, • it is easy to compute h • Given any h, • it is hard to find any M such that H(M) = h • Given M1, it is difficult to find M2 • such that H(M1) = H(M2) • Functions that satisfy these criteria are called message digest • They produce a fixed-length digest (fingerprint)
9. 9. Secure Hashing Algorithm (SHA) : • SHA-0 • SHA-1 • SHA-2 1993 1995 2002 • SHA-224, SHA-256, SHA-384, SHA-512 SHA-1 A message composed of b bits 9 160-bit message digest
10. 10. Steps for hashing: • • • • • Padding Dividing Computing Initialize Looping