Serpent Block Cipher Specification
Serpent is a 128-bit SPN block cipher with 32 rounds, designed for high security margin and AES competition finalist.
Cipher Architecture
Serpent processes 128-bit blocks through 32 rounds of substitution-permutation network. Each round applies eight parallel 4-bit S-boxes followed by a linear transformation and key mixing. The design prioritizes a conservative security margin over speed. It was an AES competition finalist with the largest security margin among candidates.
- block size
- 128 bits
- key sizes
- 128, 192, 256 bits
- rounds
- 32 rounds
16 bytespadded to 256SPN structureSecurity Margin
Serpent was designed with a very high security margin: attacks are known only up to about 11 rounds. The conservative round count and small S-boxes make it easier to analyze formally. It is often recommended where security is prioritized over performance. Bitsliced implementations can achieve high speed on modern processors.
- best attack
- ~11 rounds
- margin
- Very high
- bitslice
- Efficient on wide CPUs
out of 32~21 rounds spareSIMD friendly