Threefish256Cipher Class

Definition

Namespace

Bodu.Security.Cryptography

Assembly

Bodu.Security.Cryptography.dll

Package

Bodu.Security.Cryptography 1.2.0

Source

ThreefishBlockCipher.256.Avx512.cs

AVX-512 vectorised implementation of Threefish256Cipher. The four 64-bit state words are split across two Vector128<T> registers - lo holds the even-position words (b0, b2) and hi the odd-position words (b1, b3). Each round performs a vector add, a per-lane variable rotate (VPROLVQ ), an XOR, and a single 64-bit lane swap on hi that realigns it for the next round's MIX pairing.

public sealed class Threefish256Cipher : ThreefishBlockCipher, IBlockCipher, IDisposable

Inheritance

object

ThreefishBlockCipher

Threefish256Cipher

Implements

IBlockCipher

IDisposable

Inherited Members

ThreefishBlockCipher.Dispose()

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Extension Methods

ComparableExtensions.AtLeast<T>(T, T, IComparer<T>)

ComparableExtensions.AtMost<T>(T, T, IComparer<T>)

ComparableExtensions.IsEqualTo<T>(T, T, IComparer<T>)

ComparableExtensions.Max<T>(T, T, IComparer<T>)

ComparableExtensions.Min<T>(T, T, IComparer<T>)

Examples

// Direct single-block use - most callers should prefer the Threefish256 SymmetricAlgorithm.
byte[] key   = new byte[32];   // 256-bit key
byte[] tweak = new byte[16];   // 128-bit tweak
RandomNumberGenerator.Fill(key);
RandomNumberGenerator.Fill(tweak);

using var cipher = new Threefish256Cipher(key, tweak);

byte[] plaintext  = new byte[32];   // one 256-bit block
byte[] ciphertext = new byte[32];
cipher.Encrypt(plaintext, ciphertext);

byte[] roundtrip = new byte[32];
cipher.Decrypt(ciphertext, roundtrip);
// roundtrip equals plaintext

Remarks

Threefish-256 alternates between two MIX pair patterns within a 4-round group: (0,1)(2,3) at rounds 0 and 2, and (0,3)(2,1) at rounds 1 and 3. With the state split into even/odd halves, the alternation reduces to a single swap of hi's two lanes - applied four times in a row, the swaps cycle back to canonical layout, which is exactly where the subkey injection lands.

Gated on IsSupported because the per-lane variable rotate runs on Vector128<T>. SIMD gain on Threefish-256 is the smallest of the three variants - the 128-bit working width matches scalar register count and the per-instruction overhead is high relative to the work - but the implementation keeps the family pattern consistent and provides a measured reduction in scalar instruction count per round.

Constructors

Threefish256Cipher(ReadOnlySpan<byte>, ReadOnlySpan<byte>)

Initializes a new instance of the Threefish256Cipher class using the specified key and tweak.

public Threefish256Cipher(ReadOnlySpan<byte> key, ReadOnlySpan<byte> tweak)

Parameters

key ReadOnlySpan<byte>

The 256-bit (32-byte) key used for encryption and decryption.

tweak ReadOnlySpan<byte>

The 128-bit (16-byte) tweak value used to modify the block cipher behavior.

Fields

KeySize

Length of the Threefish-256 key is 256 bits (32 bytes).

public const int KeySize = 256

Field Value

int

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.

BlockWords

Gets the number of 64-bit words in a single block.

protected override int BlockWords { get; }

Property Value

int

RotationSchedule

Gets the rotation constants used for MIX/UNMIX operations in this cipher variant.

protected override int[] RotationSchedule { get; }

Property Value

int[]

Rounds

Gets the total number of cipher rounds.

protected override int Rounds { get; }

Property Value

int

Methods

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

Decrypts a single 32-byte ciphertext block using the Threefish-256 cipher and writes the result to the specified output buffer.

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

Parameters

input ReadOnlySpan<byte>

The 32-byte ciphertext block to decrypt.

output Span<byte>

The 32-byte buffer to receive the decrypted plaintext block.

Remarks

Dispatches to an AVX-512 vectorised implementation when supported by the host, falling back to a scalar register-resident implementation otherwise. Dispatch is gated by Bodu.Security.Cryptography.SimdCapabilities.Avx512FVL, which combines the hardware intrinsic with the process-wide SIMD opt-out; on hosts without AVX-512 it still folds to a compile-time constant that removes the branch, otherwise it reduces to a single cached-boolean load.

Exceptions

ObjectDisposedException

Thrown if the cipher has been disposed.

ArgumentException

Thrown if input or output is not 32 bytes.

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

Encrypts a single 32-byte plaintext block using the Threefish-256 cipher and writes the result to the specified output buffer.

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

Parameters

input ReadOnlySpan<byte>

The 32-byte plaintext block to encrypt.

output Span<byte>

The 32-byte buffer to receive the encrypted ciphertext block.

Remarks

Dispatches to an AVX-512 vectorised implementation when supported by the host, falling back to a scalar register-resident implementation otherwise. Dispatch is gated by Bodu.Security.Cryptography.SimdCapabilities.Avx512FVL, which combines the hardware intrinsic with the process-wide SIMD opt-out; on hosts without AVX-512 it still folds to a compile-time constant that removes the branch, otherwise it reduces to a single cached-boolean load.

Exceptions

ObjectDisposedException

Thrown if the cipher has been disposed.

ArgumentException

Thrown if input or output is not 32 bytes.

Applies to

Product	Versions
.NET	8, 10

See Also

Composing primitives - direct use vs. SymmetricAlgorithm

Threefish256