Cryptographic Hash Function
A Cryptographic Hash Function is a mathematical algorithm that takes an input, or 'message', and returns a fixed-size string of bytes, typically used to index data in hash tables. Here are key aspects of cryptographic hash functions:
Properties
- Deterministic: The same message always results in the same hash value.
- Quick Computation: Hash computation is fast for any size of data.
- Pre-Image Resistance: It should be computationally infeasible to recreate the original input from its hash value.
- Small Changes in Input Lead to Large Changes in Output: Also known as the Avalanche Effect, this property ensures that even a minor change in the input results in a significantly different hash value.
- Collision Resistance: It is computationally infeasible to find two different messages with the same hash value.
History
The concept of hash functions dates back to the 1950s, but cryptographic hash functions were formalized in the 1970s with the development of the MD5 algorithm by Ron Rivest. Here are some milestones:
- 1970s - 1980s: Development of the first cryptographic hash functions like MD4 and MD5.
- 1991: Introduction of the SHA-1 hash function by the National Institute of Standards and Technology (NIST).
- 2001: Introduction of the SHA-2 family, which includes SHA-224, SHA-256, SHA-384, and SHA-512, due to weaknesses found in SHA-1.
- 2012: NIST announced the SHA-3 competition, leading to the adoption of the Keccak algorithm as the new standard.
Applications
- Data Integrity: To verify data has not been altered or tampered with.
- Password Hashing: To secure passwords by storing their hash values instead of plain text.
- Digital Signatures: As part of cryptographic protocols for verifying the authenticity of digital documents.
- Blockchain: Used in Blockchain technologies to link blocks securely.
Common Hash Functions
- MD5: No longer considered secure for cryptographic purposes but still used for checksums.
- SHA-1: Widely used until vulnerabilities were discovered, leading to its phase-out in many applications.
- SHA-2: Includes variants like SHA-256, considered secure for many applications.
- SHA-3: The latest standard, offering better security margins and resistance to attacks like length extension attacks.
Security Considerations
While hash functions are designed to be secure, several attacks can compromise their effectiveness:
- Collision Attacks: Finding two inputs that produce the same hash output.
- Pre-image Attacks: Finding an input that produces a specific hash output.
- Length Extension Attacks: Exploiting the structure of some hash functions to extend the input in a way that produces predictable output.
External Links
Related Topics