Second pre-image resistance
Second pre-image resistance is the property that, given an input and its hash, finding a different input with the same hash is computationally infeasible.
Real-World Cryptography
Second pre-image resistance is the property that, given an input and its hash output, it is computationally infeasible to find a different input with the same output.
- How it is used
- Protects file integrity, signed transactions, and authenticated key-exchange values from substitution attacks.
- How deep it goes
- Defines the threat model, contrasts related properties, and demonstrates encoding and digest-size failure modes without proving hash internals.
- Examples
- Uses downloaded files, SHA-256 commands, ambiguous transactions, TupleHash encoding, and truncated short authenticated strings.
- What you can do after
- Diagnose substitution risks by checking digest size, trustworthy digest distribution, and unambiguous serialization before hashing.
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Hacking Cryptography
The property that, given an input and its hash output, it is computationally infeasible to find a different input with the same hash output.
- How it is used
- Uses hash functions to prevent replacing a known input with a different input that preserves its digest.
- How deep it goes
- Defines the attacker’s fixed-input goal and contrasts it with preimage and collision resistance, but gives no construction or attack procedure.
- Examples
- Uses password hashes and bounded-output mappings to illustrate fixed-input substitution and inevitable theoretical collisions.
- What you can do after
- Evaluate hash-function guarantees by identifying whether an attack fixes one input or searches for any matching pair.
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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.
- pre-image resistancecontrasts with · Pre-image resistance is the property that it is computationally infeasible to find an input producing a specified hash output.
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