/// <summary>
/// Generates a seed, in accordance with RFC 7292, §B.2
/// </summary>
/// <param name="H">Hash function</param>
/// <param name="r">Iteration count</param>
/// <param name="P">Formatted password.</param>
/// <param name="S">Salt.</param>
/// <param name="n">Number of pseudo-random bits to generate.</param>
/// <param name="ID">Purpose of key:
///
/// If ID=1, then the pseudorandom bits being produced are to be used
/// as key material for performing encryption or decryption.
///
/// 2. If ID=2, then the pseudorandom bits being produced are to be used
/// as an IV (Initial Value) for encryption or decryption.
///
/// 3. If ID=3, then the pseudorandom bits being produced are to be used
/// as an integrity key for MACing.
/// </param>
internal static byte[] PRF(HashFunction H, int r, byte[] P, byte[] S, int n, byte ID)
{
int u, v;
if ((n & 7) != 0)
{
throw new ArgumentException("Must be a factor of 8.", nameof(n));
}
switch (H)
{
case HashFunction.MD5:
u = 128;
v = 512;
break;
case HashFunction.SHA1:
u = 160;
v = 512;
break;
case HashFunction.SHA256:
u = 256;
v = 512;
break;
case HashFunction.SHA384:
u = 384;
v = 1024;
break;
case HashFunction.SHA512:
u = 512;
v = 1024;
break;
default:
throw new ArgumentException("Hash function not supported.", nameof(H));
}
int v8 = v / 8;
int u8 = u / 8;
byte[] D = new byte[v8];
int i, j, c;
for (i = 0; i < v8; i++)
{
D[i] = ID;
}
S = Extend(S, v);
P = Extend(P, v);
byte[] I = Primitives.CONCAT(S, P);
int i8 = I.Length;
c = (n + u - 1) / u;
byte[][] As = new byte[c][];
for (i = 0; i < c; i++)
{
As[i] = Primitives.CONCAT(D, I);
for (j = 0; j < r; j++)
{
As[i] = Hashes.ComputeHash(H, As[i]);
}
byte[] B = Extend(As[i], v);
for (j = 0; j < i8; j += v8)
{
AddTo(I, j, B, true);
}
}
byte[] A = Primitives.CONCAT(As);
if (A.Length != n)
{
Array.Resize <byte>(ref A, n);
}
return(A);
}
/// <summary>
/// Formats a password, in accordance with RFC 7292, §B.1.
/// </summary>
/// <param name="Password">Password</param>
/// <returns>Formatted password</returns>
internal static byte[] FormatPassword(string Password)
{
return(Primitives.CONCAT(Encoding.BigEndianUnicode.GetBytes(Password), new byte[] { 0, 0 }));
}