Table of Contents

Serpent128Cipher Class

Definition

Namespace
Bodu.Security.Cryptography
Assembly
Bodu.Security.Cryptography.dll
Package
Bodu.Security.Cryptography 1.2.0
Source
Serpent128Cipher.cs

Implements the canonical Serpent block cipher, which operates on 128-bit (16-byte) blocks using a 128, 192, or 256-bit key.

public sealed class Serpent128Cipher : SerpentBlockCipherBase, IBlockCipher, IDisposable
Inheritance
Serpent128Cipher
Implements
Inherited Members
Extension Methods

Examples

// Direct single-block use. For most workloads prefer the Serpent128 SymmetricAlgorithm wrapper.
byte[] key = new byte[32];   // 128, 192, or 256 bits - Serpent pads shorter keys to 256
RandomNumberGenerator.Fill(key);

using var cipher = new Serpent128Cipher(key);

byte[] plaintext  = new byte[16];   // one 128-bit block
byte[] ciphertext = new byte[16];
cipher.Encrypt(plaintext, ciphertext);

byte[] roundtrip = new byte[16];
cipher.Decrypt(ciphertext, roundtrip);
// roundtrip equals plaintext

Remarks

Serpent is a 32-round substitution-permutation network designed by Ross Anderson, Eli Biham, and Lars Knudsen as an Advanced Encryption Standard (AES) candidate. Each round applies a round-key XOR, one of the eight 4-bit S-boxes S0..S7, and the bitsliced linear transformation L. The final round replaces L with a post-round key XOR. Shorter keys are padded to 256 bits by appending a 1 bit followed by zeros, per the Serpent specification.

This class implements the standard Serpent-128 block primitive only. It is interoperable with canonical Serpent test vectors and does not use the tweak schedule or widened state used by the non-standard wide-block variants.

Most callers should prefer the higher-level Serpent128 class, which exposes the standard SymmetricAlgorithm contract. Use Serpent128Cipher directly only when composing the raw block primitive with an IBlockCipherModeTransform or IPaddingStrategy.

This implementation computes each S-box as a Boolean circuit (Osvik's) and the linear transform with rotations, shifts and XOR, so it reads no tables and takes no branches that depend on the key or the data: its running time does not depend on either.

Constructors

Serpent128Cipher(ReadOnlySpan<byte>)

Initializes a new instance of the Serpent128Cipher class using the specified key.

public Serpent128Cipher(ReadOnlySpan<byte> key)

Parameters

key ReadOnlySpan<byte>

The Serpent key. Length must be 16, 24, or 32 bytes (128, 192, or 256 bits). Shorter keys are padded to 256 bits per the Serpent specification.

Exceptions

ArgumentException

key does not have a length of 16, 24, or 32 bytes.

Properties

BlockSize

Gets the block size, in bits, of the cipher (for example, 128 bits / 16 bytes for AES).

public override int BlockSize { get; }

Property Value

int

The block size, in bits.

Remarks

The block size is expressed in bits to align with the BCL convention used by BlockSize. Byte-array operations (encrypt, decrypt, slice) convert to bytes at the call site as BlockSize / 8.

Methods

Decrypt(ReadOnlySpan<byte>, Span<byte>)

Decrypts a single block of ciphertext into the specified output span.

public override void Decrypt(ReadOnlySpan<byte> input, Span<byte> output)

Parameters

input ReadOnlySpan<byte>

A read-only span containing the ciphertext block. Its byte length must equal BlockSize / 8.

output Span<byte>

A writable span that receives the plaintext block. Its byte length must equal BlockSize / 8.

Remarks

In-place decryption (passing the same buffer as both input and output) is supported only when the implementation explicitly permits it; otherwise the spans must not overlap.

Exceptions

ArgumentException

Thrown if the length of input or output does not match BlockSize.

Dispose(bool)

Releases all internal buffers and sensitive material.

protected override void Dispose(bool disposing)

Parameters

disposing bool

true when invoked from Dispose(); false when invoked from the finalizer.

Remarks

The base implementation records the disposed state. Derived Serpent implementations should override this method to clear expanded round keys, tweak material, and other sensitive buffers before calling base.Dispose(disposing).

Encrypt(ReadOnlySpan<byte>, Span<byte>)

Encrypts a single block of plaintext into the specified output span.

public override void Encrypt(ReadOnlySpan<byte> input, Span<byte> output)

Parameters

input ReadOnlySpan<byte>

A read-only span containing the plaintext block. Its byte length must equal BlockSize / 8.

output Span<byte>

A writable span that receives the ciphertext block. Its byte length must equal BlockSize / 8.

Remarks

In-place encryption (passing the same buffer as both input and output) is supported only when the implementation explicitly permits it; otherwise the spans must not overlap.

Exceptions

ArgumentException

Thrown if the length of input or output does not match BlockSize.

Explicit Interface Implementations

IBlockCipher.DecryptBlocks(ReadOnlySpan<byte>, Span<byte>)

Decrypts a run of one or more contiguous blocks, each independently (ECB semantics), writing the plaintext into output.

void IBlockCipher.DecryptBlocks(ReadOnlySpan<byte> input, Span<byte> output)

Parameters

input ReadOnlySpan<byte>

The ciphertext blocks. Length must be a positive multiple of BlockSize / 8.

output Span<byte>

The destination for the plaintext. Must be at least input.Length bytes.

Remarks

The default implementation calls Decrypt(ReadOnlySpan<byte>, Span<byte>) once per block; see EncryptBlocks(ReadOnlySpan<byte>, Span<byte>) for when to override.

Exceptions

ObjectDisposedException

The instance has been disposed.

ArgumentException

input is not a whole number of blocks, or output is shorter than input.

IBlockCipher.EncryptBlocks(ReadOnlySpan<byte>, Span<byte>)

Encrypts a run of one or more contiguous blocks, each independently (ECB semantics), writing the ciphertext into output.

void IBlockCipher.EncryptBlocks(ReadOnlySpan<byte> input, Span<byte> output)

Parameters

input ReadOnlySpan<byte>

The plaintext blocks. Length must be a positive multiple of BlockSize / 8.

output Span<byte>

The destination for the ciphertext. Must be at least input.Length bytes.

Remarks

The default implementation calls Encrypt(ReadOnlySpan<byte>, Span<byte>) once per block. Implementations backed by a primitive with per-call setup cost (for example a wrapped BCL cipher context) should override this to amortize that cost across the whole run. Callers that process independent blocks - ECB and the keystream layer of CTR-based modes - should prefer this over a per-block loop.

Exceptions

ObjectDisposedException

The instance has been disposed.

ArgumentException

input is not a whole number of blocks, or output is shorter than input.

Applies to

ProductVersions
.NET8, 10

See Also

Serpent128