Overview
SHA-256 processes message blocks through a compression function to produce a 256-bit digest. Small input changes are designed to produce unpredictable digest changes.
FoundationSource checked
SHA-256
Computes a fixed 256-bit cryptographic hash of an input message.
Quick Facts
Compact metadata for implementation and discovery.
- Category
- Cryptography
- Difficulty
- Advanced
- Family
- Cryptographic Hash
- Tier
- Foundation
- Status
- Verified
- Review
- Source Checked
- Sources
- 1
- Formulas
- 1
- Relationships
- 9
- Code example
- Not ready
- Visualization
- Ready
- Aliases
- SHA256
Core Concepts
cryptographic hashmessage blockcompression functiondigest
Quick facts
Complexity
Runtime and memory behavior at a glance.
Best
O(n)
Average
O(n)
Worst
O(n)
Space
O(1)
When to Use
- Use it for integrity checks, content addressing, and cryptographic protocols that specify SHA-256.
- Use HMAC-SHA-256 when a keyed message authentication code is required.
- Use vetted library implementations.
When Not to Use
- Avoid using plain SHA-256 as password storage without a password-hashing scheme.
- Avoid treating a hash digest as encryption.
- Avoid using it as a MAC without a construction such as HMAC.
What It Does
- Hashes data to a fixed-size digest
- Makes small input changes produce very different output
Use Cases
- Integrity checks
- Digital signatures
- Content addressing
Inputs
- Message bytes
Outputs
- 256-bit digest
Key Formulas (1)
Compression round value
T1 = h + Σ₁(e) + Ch(e, f, g) + K[t] + W[t]
T1 = h + Sigma1(e) + Ch(e, f, g) + K[t] + W[t]Combines state words, constants, and message schedule data in each compression round.
Pseudocode
- 1.Pad the message to a block boundary
- 2.Initialize fixed hash state values
- 3.Process each block through compression rounds
- 4.Update the hash state after each block
- 5.Return the final digest
Canonical Example
- Input
- message bytes = "abc"
- Output
- a 256-bit digest
- Explanation
- SHA-256 deterministically maps the byte string to a fixed-length digest used for integrity or identification.
Implementation Notes
- Feed bytes in the exact encoding expected by the protocol.
- Use streaming APIs for large inputs.
- Use constant-time comparison when checking keyed digests.
Common Pitfalls
- Assuming hashes can be decrypted.
- Using raw hashes for passwords instead of salted, slow password hashing.
- Comparing secret-dependent digests with non-constant-time equality checks.
Interactive Mechanism Walkthrough
Graph Frontier & Edge RelaxationShow message blocks updating a fixed-size hash state.
Step 1 of 5: Pad the message to a block boundary
hash-blocksNotes
SHA-256 is not encryption; it is a one-way digest function.
Sources (1)
What each reference supports for this entry.
NIST FIPS 180-4
DocumentationNIST Secure Hash Standard reference for SHA-256 and related SHA-2 hash algorithms.
Open sourceExplore Next
Good next jumps from the relationship graph, ranked for useful discovery.
Alternative toBLAKE3
Cryptography · Extended
Both are cryptographic hash functions with different designs.
Compare with thisUsed byFiat-Shamir Transform
Cryptography · Core
Fiat-Shamir-style constructions use transcript hashing to derive verifier challenges.
Compare with thisUsed byHash-DRBG
Cryptography · Core
Hash-DRBG can be instantiated with SHA-family hash functions.
Compare with thisUsed byHMAC
Cryptography · Core
HMAC can be instantiated with SHA-256 as its underlying hash.
Compare with thisRelationships
View full relationship pageAlternative toBLAKE3
Both are cryptographic hash functions with different designs.
SpecializesMerkle-Damgard Construction
SHA-256 follows a Merkle-Damgard-style compression construction.
Tags
CryptographyHashingSecurity