public SymmetricCipherResult ProcessPayload(IFfxModeBlockCipherParameters param)
{
var key = param.Key.ToBytes();
var engineParam = new EngineInitParameters(param.Direction, key, param.UseInverseCipherMode);
_engine.Init(engineParam);
CheckPayloadRequirements(param.Payload);
if (param.Direction == BlockCipherDirections.Encrypt)
{
return(new SymmetricCipherResult(Encrypt(param)));
}
return(new SymmetricCipherResult(Decrypt(param)));
}
protected abstract BitString Decrypt(IFfxModeBlockCipherParameters param);
protected override BitString Decrypt(IFfxModeBlockCipherParameters param)
{
var mode = _factory.GetStandardCipher(_engine, BlockCipherModesOfOperation.Ecb);
var X = NumeralString.ToNumeralString(param.Payload);
var n = X.Numbers.Length;
// 1. Let u = ⌈n / 2⌉; v = n – u.
var u = n.CeilingDivide(2);
var v = n - u;
// 2. Let A = X[1..u]; B = X[u + 1..n].
var A = new NumeralString(X.Numbers.Take(u).ToArray());
var B = new NumeralString(X.Numbers.Skip(u).Take(v).ToArray());
// Let TL = T[0..31] and TR = T[32..63]
var TL = param.Iv.Substring(32, 32);
var TR = param.Iv.Substring(0, 32);
// 4. For i from 0 to 7:
for (var i = NumberOfRounds - 1; i >= 0; i--)
{
// i. If i is even, let m = u and W = TR, else let m = v and W = TL.
// v. If i is even, let m = u; else, let m = v.
var m = i % 2 == 0 ? u : v;
var W = i % 2 == 0 ? TR : TL;
// ii. Let P = W ⊕ [i] 4 || [NUMradix(REV(B))]12 .
var numA = new BitString(_ffInternals.Num(param.Radix, _ffInternals.Rev(A)));
if (numA.BitLength < 12 * BitsInByte)
{
var bitsToPrepend = new BitString(12 * BitsInByte - numA.BitLength);
numA = bitsToPrepend.ConcatenateBits(numA);
}
var P = W.XOR(new BitString(new byte[3]).ConcatenateBits(((byte)i).ToBitString()))
.ConcatenateBits(numA);
// iii. Let S = REVB(CIPHREVB(K) REVB(P)).
var S = _ffInternals.RevB(mode.ProcessPayload(
new ModeBlockCipherParameters(
BlockCipherDirections.Encrypt,
_ffInternals.RevB(param.Key),
_ffInternals.RevB(P))).Result);
// iv. Let y = NUM(S).
var y = _ffInternals.Num(S);
// v. Let c = (NUMradix (REV(B)) - y) mod radix m .
var c = (_ffInternals.Num(param.Radix, _ffInternals.Rev(B)) - y).PosMod(BigInteger.Pow(param.Radix, m));
// vi. Let C = REV(STRm radix(c)).
var C = _ffInternals.Rev(_ffInternals.Str(param.Radix, m, c));
// vii. Let B = A.
B = A;
// viii. Let A = C.
A = C;
}
// 5. Return A || B.
return(NumeralString.ToBitString(A)
.ConcatenateBits(NumeralString.ToBitString(B)));
}
protected override BitString Encrypt(IFfxModeBlockCipherParameters param)
{
var mode = _factory.GetStandardCipher(_engine, BlockCipherModesOfOperation.Ecb);
var X = NumeralString.ToNumeralString(param.Payload);
var n = X.Numbers.Length;
var t = param.Iv.BitLength / BitsInByte;
// 1. Let u = Floor(n/2); v = n – u.
var u = n / 2;
var v = n - u;
// 2. Let A = X[1..u]; B = X[u + 1..n].
var A = new NumeralString(X.Numbers.Take(u).ToArray());
var B = new NumeralString(X.Numbers.Skip(u).Take(v).ToArray());
// 3. Let b = Ceiling(Ceiling(v×LOG(radix))/8).
var b = (int)System.Math.Ceiling(System.Math.Ceiling(v * System.Math.Log(param.Radix, 2)) / 8);
// 4. Let d = 4*Ceiling(b/4) + 4.
var d = 4 * b.CeilingDivide(4) + 4;
// the number times to iterate through the concatenation of cipher iterator blocks
var jCount = d.CeilingDivide(16);
// 5. Let P = [1] 1 || [2] 1 || [1] 1 || [radix] 3 || [10] 1 || [u mod 256] 1 || [n] 4 || [t] 4.
var pBytes = new byte[_engine.BlockSizeBytes];
pBytes[0] = 0x01;
pBytes[1] = 0x02;
pBytes[2] = 0x01;
// 3 bytes for radix, but radix is capped at 16 bits (2^16), so add a 0 byte
pBytes[3] = 0x00;
Array.Copy(BitString.To32BitString(param.Radix).GetLeastSignificantBits(16).ToBytes(), 0, pBytes, 4, 2);
pBytes[6] = 0x0a;
pBytes[7] = (byte)(u % 256);
Array.Copy(BitString.To32BitString(n).ToBytes(), 0, pBytes, 8, 4);
Array.Copy(BitString.To32BitString(t).ToBytes(), 0, pBytes, 12, 4);
var P = new BitString(pBytes);
// 6. For i from 0 to 9:
for (var i = 0; i < NumberOfRounds; i++)
{
// i. Let Q = T || [0] (−t−b−1) mod 16 || [i] 1 || [NUMradix(B)]b.
var numB = new BitString(_ffInternals.Num(param.Radix, B));
if (numB.BitLength < b * BitsInByte)
{
var bitsToPrepend = new BitString(b * BitsInByte - numB.BitLength);
numB = bitsToPrepend.ConcatenateBits(numB);
}
var Q = new BitString(0)
.ConcatenateBits(param.Iv)
.ConcatenateBits(new BitString((-t - b - 1).PosMod(16) * BitsInByte))
.ConcatenateBits(((byte)i).ToBitString())
.ConcatenateBits(numB.GetMostSignificantBits(b * BitsInByte));
// ii. Let R = PRF(P || Q).
var R = _ffInternals.Prf(P.ConcatenateBits(Q), param.Key);
// iii. Let S be the first d bytes of the following string of Ceiling(d/16) blocks:
// R || CIPHK(R Å [1]16) || CIPHK (R Å [2]16) … CIPHK(R Å [éd/16ù–1]).
var S = R.GetDeepCopy();
for (var j = 1; j < jCount; j++)
{
var pad = BitString.To32BitString(j).PadToModulusMsb(_engine.BlockSizeBits);
S = S.ConcatenateBits(
mode.ProcessPayload(
new ModeBlockCipherParameters(
BlockCipherDirections.Encrypt,
param.Key,
R.XOR(pad))).Result
);
}
S = S.GetMostSignificantBits(d * BitsInByte);
// iv. Let y = NUM(S).
var y = _ffInternals.Num(S);
// v. If i is even, let m = u; else, let m = v.
var m = i % 2 == 0 ? u : v;
// vi. Let c = (NUMradix (A)+y) mod radix m .
var c = (_ffInternals.Num(param.Radix, A) + y).PosMod(BigInteger.Pow(param.Radix, m));
// vii. Let C = STR m radix (c).
var C = _ffInternals.Str(param.Radix, m, c);
// viii. Let A = B.
A = B;
// ix. Let B = C.
B = C;
}
// 7. Return A || B.
return(NumeralString.ToBitString(A)
.ConcatenateBits(NumeralString.ToBitString(B)));
}
