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A property of cryptographic hash functions where it is computationally infeasible to find two distinct inputs producing the same output.
DESCRIPTION
Collision resistance ensures that cryptographic hashes rarely collide in practice, even though collisions must exist due to the pigeonhole principle. It underpins digital signatures, certificates, and content-addressed storage. Broken collision resistance, as with MD5 and SHA-1, enables forgery and tampering attacks. Security requires choosing modern hash functions and appropriate parameters. Standards like FIPS 180‑4 and NIST SP 800‑107 guide algorithm selection and usage. Continuous monitoring of cryptanalytic advances is essential.
ALTERNATIVE DEFINITIONS
Wikipedia
A hash function is collision-resistant if it is hard to find two different inputs that hash to the same output.
Plain-language definition emphasizing computational hardness.
NIST
Collision resistance means that it is computationally infeasible to find any two distinct inputs that map to the same hash output.
Formal standard phrasing with infeasibility emphasis.
RELATED TERMS
Cryptographic Hash Function Preimage Resistance Second Preimage Resistance SHA-256 MD5 SHA-1 Digital Signature Message Integrity FIPS 180-4 NIST SP 800-107
COMPETING TERMS
Weak Collision Resistance
KNOWLEDGE AREAS
Data Security Software Engineering Testing & Validation
TARGET AUDIENCE
Security Architect Cybersecurity Engineer Chief Information Security Officer Software Developer Cloud Architect
EXTERNAL SOURCES
- Wikipedia - Collision resistance
- NIST - Secure Hash Standard (FIPS 180-4)
- IETF - MD5 security considerations
TOP QUESTIONS
Why does Collision Resistance matter?
It prevents attackers from forging messages with the same hash, protecting digital signatures and integrity checks. Weaknesses enable practical collision attacks and spoofing.
Category: Relevancy
How is Collision Resistance different from Preimage Resistance?
Collision resistance prevents finding any two inputs with the same hash, while preimage resistance prevents finding an input matching a specific hash.
Category: Misunderstanding
Which hash functions are considered collision resistant today?
SHA-256 and SHA-3 families are recommended. MD5 and SHA-1 are broken for collision resistance and should be avoided for security-critical uses.
Category: Requirements
What are common mistakes related to Collision Resistance?
Using MD5/SHA-1 for signatures, failing to version hash algorithms, or misunderstanding that longer outputs generally improve collision resistance.
Category: Mistakes
How does Collision Resistance impact digital signatures?
Signatures typically operate over message hashes; collisions can allow signature reuse attacks. Strong hash choices are essential to maintain signature trust.
Category: Security
Is a hash function with 128-bit output still safe?
128-bit outputs may be marginal for long-term collision resistance due to birthday attacks. Prefer 256-bit outputs for robust security margins.
Category: Risks
How do I migrate away from weak hash algorithms?
Perform inventory, implement dual-hash strategies, update certificates and protocols, and deprecate weak hashes with clear timelines and compatibility plans.
Category: Management
What is the birthday bound for collisions?
Collisions can be expected after about 2^(n/2) operations for an n‑bit hash, guiding minimum output size choices.
Category: Mathematics
Where can I learn more about hash function security?
Read NIST standards, IETF RFCs, and current cryptanalysis literature. Follow reputable security advisories and vendor guidance.
Category: Learning