Cryptography
MD5
Also known as: Message Digest 5
Definition
A 128-bit cryptographic hash function designed by Ron Rivest in 1992; now broken — practical collisions are trivial and it must not be used for any security-sensitive purpose.
Examples
- MD5 hashes are still used to verify file downloads where only accidental corruption is a concern, not malicious tampering.
- The Flame malware (2012) forged a Microsoft code-signing certificate via an MD5 chosen-prefix collision.
Related terms
Cryptographic Hash Function
A deterministic one-way function that maps arbitrary-length input to a fixed-length digest, designed to be collision-, preimage-, and second-preimage-resistant.
HMAC
A keyed Message Authentication Code construction built on top of a cryptographic hash function, defined in RFC 2104 and FIPS 198-1.
Digital Signature
A public-key cryptographic mechanism that proves the authenticity, integrity and non-repudiation of a message or document.
Salt
A unique random value combined with a password before hashing to defeat rainbow tables and ensure each user's hash is distinct.
Key Derivation Function (KDF)
A cryptographic function that derives one or more strong cryptographic keys from a secret input such as a password, shared secret or master key.
Encryption
The cryptographic transformation of plaintext into ciphertext using an algorithm and key so that only authorized parties can recover the original data.