1 files changed, 91 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/agreement/srp/SRP6Util.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/agreement/srp/SRP6Util.java
new file mode 100644
index 000000000..40ec01c0f
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/agreement/srp/SRP6Util.java
@@ -0,0 +1,91 @@
+package org.spongycastle.crypto.agreement.srp;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.CryptoException;
+import org.spongycastle.crypto.Digest;
+import org.spongycastle.util.BigIntegers;
+
+public class SRP6Util
+{
+    private static BigInteger ZERO = BigInteger.valueOf(0);
+    private static BigInteger ONE = BigInteger.valueOf(1);
+
+    public static BigInteger calculateK(Digest digest, BigInteger N, BigInteger g)
+    {
+        return hashPaddedPair(digest, N, N, g);
+    }
+
+    public static BigInteger calculateU(Digest digest, BigInteger N, BigInteger A, BigInteger B)
+    {
+        return hashPaddedPair(digest, N, A, B);
+    }
+
+    public static BigInteger calculateX(Digest digest, BigInteger N, byte[] salt, byte[] identity, byte[] password)
+    {
+        byte[] output = new byte[digest.getDigestSize()];
+
+        digest.update(identity, 0, identity.length);
+        digest.update((byte)':');
+        digest.update(password, 0, password.length);
+        digest.doFinal(output, 0);
+
+        digest.update(salt, 0, salt.length);
+        digest.update(output, 0, output.length);
+        digest.doFinal(output, 0);
+
+        return new BigInteger(1, output);
+    }
+
+    public static BigInteger generatePrivateValue(Digest digest, BigInteger N, BigInteger g, SecureRandom random)
+    {
+        int minBits = Math.min(256, N.bitLength() / 2);
+        BigInteger min = ONE.shiftLeft(minBits - 1);
+        BigInteger max = N.subtract(ONE);
+
+        return BigIntegers.createRandomInRange(min, max, random);
+    }
+
+    public static BigInteger validatePublicValue(BigInteger N, BigInteger val)
+        throws CryptoException
+    {
+        val = val.mod(N);
+
+        // Check that val % N != 0
+        if (val.equals(ZERO))
+        {
+            throw new CryptoException("Invalid public value: 0");
+        }
+
+        return val;
+    }
+
+    private static BigInteger hashPaddedPair(Digest 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.update(n1_bytes, 0, n1_bytes.length);
+        digest.update(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];
+            System.arraycopy(bs, 0, tmp, length - bs.length, bs.length);
+            bs = tmp;
+        }
+        return bs;
+    }
+}