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Security Fundamentals & Crypto · Foundational

Message Digest 5 (MD5)

Legacy 128-bit hash function that is broken for collision resistance.

Definition

MD5 was designed by Ron Rivest in 1991. Practical collisions were demonstrated in 2004, and forged certificates using MD5 collisions appeared in 2008. It may still appear as a non-security checksum but must not be used for signatures or password storage.

Example

The Flame malware used an MD5 collision to forge a Microsoft code-signing certificate.

Exam tip

MD5 = 128-bit and broken; choose SHA-256 or SHA-3 for integrity.

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