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using System;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Agreement.Srp
{
public class Srp6Utilities
{
public static BigInteger CalculateK(IDigest digest, BigInteger N, BigInteger g)
{
return HashPaddedPair(digest, N, N, g);
}
public static BigInteger CalculateU(IDigest digest, BigInteger N, BigInteger A, BigInteger B)
{
return HashPaddedPair(digest, N, A, B);
}
public static BigInteger CalculateX(IDigest digest, BigInteger N, byte[] salt, byte[] identity, byte[] password)
{
byte[] output = new byte[digest.GetDigestSize()];
digest.BlockUpdate(identity, 0, identity.Length);
digest.Update((byte)':');
digest.BlockUpdate(password, 0, password.Length);
digest.DoFinal(output, 0);
digest.BlockUpdate(salt, 0, salt.Length);
digest.BlockUpdate(output, 0, output.Length);
digest.DoFinal(output, 0);
return new BigInteger(1, output);
}
public static BigInteger GeneratePrivateValue(IDigest digest, BigInteger N, BigInteger g, SecureRandom random)
{
int minBits = System.Math.Min(256, N.BitLength / 2);
BigInteger min = BigInteger.One.ShiftLeft(minBits - 1);
BigInteger max = N.Subtract(BigInteger.One);
return BigIntegers.CreateRandomInRange(min, max, random);
}
public static BigInteger ValidatePublicValue(BigInteger N, BigInteger val)
{
val = val.Mod(N);
// Check that val % N != 0
if (val.Equals(BigInteger.Zero))
throw new CryptoException("Invalid public value: 0");
return val;
}
private static BigInteger HashPaddedPair(IDigest digest, BigInteger N, BigInteger n1, BigInteger n2)
{
int padLength = (N.BitLength + 7) / 8;
byte[] n1_bytes = GetPadded(n1, padLength);
byte[] n2_bytes = GetPadded(n2, padLength);
digest.BlockUpdate(n1_bytes, 0, n1_bytes.Length);
digest.BlockUpdate(n2_bytes, 0, n2_bytes.Length);
byte[] output = new byte[digest.GetDigestSize()];
digest.DoFinal(output, 0);
return new BigInteger(1, output);
}
private static byte[] GetPadded(BigInteger n, int length)
{
byte[] bs = BigIntegers.AsUnsignedByteArray(n);
if (bs.Length < length)
{
byte[] tmp = new byte[length];
Array.Copy(bs, 0, tmp, length - bs.Length, bs.Length);
bs = tmp;
}
return bs;
}
}
}
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