Collision-resistant hash function
A collision-resistant hash function is a cryptographic hash function for which finding two distinct inputs with the same output is computationally infeasible.
Real-World Cryptography
Collision resistance is the property that it is computationally infeasible to find two distinct inputs that produce the same hash output.
- How it is used
- Protects systems that need distinct inputs to remain distinguishable through their hash outputs.
- How deep it goes
- Defines attacker choice, contrasts second pre-image resistance, and explains digest-size limits without proving security.
- Examples
- Uses two-bit outputs, random input pairs, published MD5 and SHA-1 collisions, and a visual two-input-to-one-digest diagram.
- What you can do after
- Evaluate hash choices by attacker control, digest size, and known collision attacks.
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Hacking Cryptography
The property that it is computationally infeasible to find any two distinct inputs that produce the same hash output.
- How it is used
- Defines the security goal that prevents attackers from deliberately producing two different inputs with one digest.
- How deep it goes
- Explains unavoidable collisions, birthday attacks, file-format exploitation, and sponge capacity, but gives no executable attack procedure.
- Examples
- Uses shared birthdays, differently rendered PDFs, and SHA-3 or SHAKE parameter tables to make collision risk concrete.
- What you can do after
- Evaluate hash designs by comparing their stated collision-resistance level with birthday-attack expectations and construction parameters.
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Software Security for Developers
Collision resistance is the computational infeasibility of finding two distinct inputs that produce the same cryptographic hash value.
- How it is used
- Explains why cryptographic hashes can support computer-security tasks such as message integrity and authentication.
- How deep it goes
- Defines collision resistance and contrasts it with one-wayness, but defers the mathematics of hash-function design and assessment.
- Examples
- Uses SHA-256 outputs for lowercase “a,” uppercase “A,” and a 2.6 GB Ubuntu ISO.
- What you can do after
- Evaluate hash-function choices and select standardized, peer-reviewed implementations instead of creating a custom cryptographic hash.
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Related concepts
- hash functionproduced by · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
- security propertykind of · A security property is a security-relevant characteristic that a cryptographic primitive or protocol is intended to provide.
- capacityconfigured by · In a sponge construction, capacity is the portion of the internal state not directly exposed to input or output and determining security strength.
- hash-based signature schemecontrasts with · A hash-based signature scheme is a digital signature scheme whose security is based on cryptographic hash-function properties rather than algebraic number-theoretic assumptions.
- cryptographic hashpart of · A cryptographic hash is a fixed-length digest computed from input data by a deterministic function designed to resist preimage, second-preimage, and collision attacks.
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