What is SHA-1?
SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function that produces a 160-bit hash value (represented as a 40-character hexadecimal string). Published in 1995 by the NSA, SHA-1 became one of the most widely used hash algorithms. However, it is now considered cryptographically broken and should not be used for security purposes.
History and Development
- 1993: SHA designed by NSA, published by NIST
- 1995: SHA-1 published as improvement over SHA
- 2005: Collision attacks discovered
- 2017: SHA-1 officially deprecated by major companies
- Present: Phased out in favor of SHA-2 and SHA-3
Technical Specifications
- Output: 160 bits (20 bytes) or 40 hexadecimal characters
- Input: Any size input data
- Block Size: 512 bits
- Word Size: 32 bits
- Rounds: 80 rounds of hashing operations
Security Concerns
- Collision Attacks: Practical collision attacks discovered in 2017
- Deprecation: Major browsers stopped accepting SHA-1 certificates in 2017
- Alternatives: SHA-256 and SHA-512 are recommended replacements
- Legacy Use: Still used for non-security purposes like Git repositories
Why Avoid SHA-1 for Security
SHA-1 suffers from fundamental weaknesses that make it unsuitable for cryptographic purposes. Collision attacks allow attackers to create two different inputs that produce the same hash. Additionally, the 160-bit output size (compared to SHA-256's 256-bit) provides insufficient resistance against brute-force attacks by modern standards.