What is SHA-256?
SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function that produces a 256-bit (32-byte) hash value, typically rendered as a 64-character hexadecimal number. It is part of the SHA-2 family designed by the NSA and is widely used for data integrity verification and digital signatures.
Quick Facts
| Full Name | Secure Hash Algorithm 256-bit |
|---|---|
| Created | 2001 by NSA, published by NIST |
| Specification | Official Specification |
How It Works
SHA-256 was published by NIST in 2001 as part of the SHA-2 family, which also includes SHA-224, SHA-384, and SHA-512. It processes data in 512-bit blocks through 64 rounds of computation. SHA-256 is considered cryptographically secure and is used in many security applications including SSL/TLS certificates, Bitcoin mining, and password hashing. Unlike MD5, no practical collision attacks have been found against SHA-256.
Key Characteristics
- Produces a fixed 256-bit (64 hexadecimal characters) output
- Cryptographically secure - no known practical attacks
- Deterministic - same input always produces same output
- Avalanche effect - small input changes cause significant output changes
- Computationally intensive compared to MD5
- Part of the SHA-2 family of hash functions
Common Use Cases
- SSL/TLS certificate signatures
- Bitcoin and cryptocurrency mining
- Digital signatures and code signing
- Password hashing with proper salting
- File integrity verification in security-critical applications
Example
Loading code...Frequently Asked Questions
Is SHA-256 still secure in 2024?
Yes, SHA-256 remains cryptographically secure with no practical collision attacks found. It is approved by NIST and widely used in security-critical applications including SSL/TLS, Bitcoin, and digital signatures. SHA-256 is expected to remain secure for the foreseeable future.
What is the difference between SHA-256 and MD5?
SHA-256 produces a 256-bit hash (64 hex characters) and is cryptographically secure, while MD5 produces a 128-bit hash (32 hex characters) and is considered broken due to known collision attacks. SHA-256 is recommended for all security-sensitive applications; MD5 should only be used for non-security purposes like checksums.
Can SHA-256 be used for password hashing?
While SHA-256 can be used for password hashing with proper salting, dedicated password hashing algorithms like bcrypt, scrypt, or Argon2 are recommended. These algorithms are intentionally slow and memory-intensive, making brute-force attacks more difficult compared to fast algorithms like SHA-256.
Why does Bitcoin use SHA-256?
Bitcoin uses SHA-256 for its proof-of-work mining algorithm and for creating transaction hashes. SHA-256 was chosen for its security, the availability of hardware implementations (ASICs), and its deterministic nature. Miners must find a nonce that produces a hash below a target difficulty level.
What is the avalanche effect in SHA-256?
The avalanche effect means that even a tiny change in input (like flipping a single bit) causes a dramatically different output hash. This property ensures that similar inputs don't produce similar outputs, making it impossible to predict or reverse-engineer the input from the hash output.