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Security Fundamentals & Crypto · Intermediate

Blowfish

Symmetric block cipher by Bruce Schneier with a 64-bit block and variable key length from 32 to 448 bits.

Definition

Blowfish (1993) is fast and unpatented but its 64-bit block size limits its use for large data volumes. It remains relevant chiefly as the basis of the bcrypt password-hashing function. Its successor is Twofish.

Example

bcrypt's expensive key setup is derived from the Blowfish key schedule.

Exam tip

Blowfish = 64-bit block, up to 448-bit key; Twofish = 128-bit block, AES finalist.

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