Cryptographic Hashes
Cryptographic hashes are mathematical algorithms that take an input, or 'message,' and produce a fixed-size string of bytes, typically used to verify the integrity of data. Here's an in-depth look at cryptographic hashes:
History and Development
The concept of hash functions dates back to the early days of computing. However, the use of hashes for cryptographic purposes began to take shape in the 1970s and 1980s:
- In 1976, Diffie-Hellman key exchange was introduced, which indirectly influenced the development of cryptographic hash functions.
- The Secure Hash Algorithm (SHA) was developed by the National Security Agency (NSA) in the early 1990s, with SHA-0 being the first version released in 1993. It was quickly replaced by SHA-1 due to security concerns.
- MD5, designed by Ronald Rivest in 1991, became widely used but was later found to have vulnerabilities.
Functionality
A cryptographic hash function does the following:
- Deterministic: Given a particular input, it always produces the same output.
- Quick to compute: The hash should be computable in a reasonable amount of time.
- Irreversible: It should be computationally infeasible to generate the original input from its hash (pre-image resistance).
- Collision-resistant: It should be hard to find two different inputs that produce the same hash output.
- Fixed output size: Regardless of the input size, the hash output is always of a fixed length.
Common Uses
- Integrity Verification: To check if data has been altered during transmission or storage.
- Password Storage: Storing hashed passwords rather than plaintext passwords.
- Blockchain: For blockchain hashing in technologies like Bitcoin.
- Digital Signatures: Ensuring the authenticity of documents or software.
Notable Algorithms
- SHA-256 - A member of the SHA-2 family, widely used in security applications.
- BLAKE - Designed for high performance on modern hardware.
- Whirlpool - Designed for use in digital signatures, message authentication, and other cryptographic applications.
Security Considerations
The security of cryptographic hashes depends on:
- The strength of the algorithm against attacks like collision attacks or preimage attacks.
- The hash length; longer hashes are generally more secure.
- The computational power available to attackers, which can change over time, leading to the need for hash function upgrades.
Challenges and Advances
Over time, as computing power increases and new attack methods are discovered:
- Older hash functions like MD5 and SHA-1 have been shown to be vulnerable to collisions, leading to their deprecation in secure applications.
- Newer standards like SHA-3, which was announced by NIST in 2015, aim to address these vulnerabilities.
External Links
Related Concepts