1 files changed, 159 insertions, 0 deletions
diff --git a/crypto/src/tls/TlsDHUtilities.cs b/crypto/src/tls/TlsDHUtilities.cs
new file mode 100644
index 000000000..7605b0055
--- /dev/null
+++ b/crypto/src/tls/TlsDHUtilities.cs
@@ -0,0 +1,159 @@
+using System;
+using System.IO;
+
+using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Tls.Crypto;
+using Org.BouncyCastle.Utilities;
+
+namespace Org.BouncyCastle.Tls
+{
+    public abstract class TlsDHUtilities
+    {
+        public static TlsDHConfig CreateNamedDHConfig(TlsContext context, int namedGroup)
+        {
+            if (namedGroup < 0 || NamedGroup.GetFiniteFieldBits(namedGroup) < 1)
+                return null;
+
+            bool padded = TlsUtilities.IsTlsV13(context);
+            return new TlsDHConfig(namedGroup, padded);
+        }
+
+        public static DHGroup GetDHGroup(TlsDHConfig dhConfig)
+        {
+            int namedGroup = dhConfig.NamedGroup;
+            if (namedGroup >= 0)
+                return GetNamedDHGroup(namedGroup);
+
+            return dhConfig.ExplicitGroup;
+        }
+
+        public static DHGroup GetNamedDHGroup(int namedGroup)
+        {
+            switch (namedGroup)
+            {
+            case NamedGroup.ffdhe2048:
+                return DHStandardGroups.rfc7919_ffdhe2048;
+            case NamedGroup.ffdhe3072:
+                return DHStandardGroups.rfc7919_ffdhe3072;
+            case NamedGroup.ffdhe4096:
+                return DHStandardGroups.rfc7919_ffdhe4096;
+            case NamedGroup.ffdhe6144:
+                return DHStandardGroups.rfc7919_ffdhe6144;
+            case NamedGroup.ffdhe8192:
+                return DHStandardGroups.rfc7919_ffdhe8192;
+            default:
+                return null;
+            }
+        }
+
+        public static int GetMinimumFiniteFieldBits(int cipherSuite)
+        {
+            /*
+             * NOTE: An equivalent mechanism was added to support a minimum bit-size requirement for ECC
+             * mooted in early drafts of RFC 8442. This requirement was removed in later drafts, so that
+             * mechanism is currently somewhat trivial, and this similarly so.
+             */
+            return IsDHCipherSuite(cipherSuite) ? 1 : 0;
+        }
+
+        public static bool IsDHCipherSuite(int cipherSuite)
+        {
+            switch (TlsUtilities.GetKeyExchangeAlgorithm(cipherSuite))
+            {
+            case KeyExchangeAlgorithm.DH_anon:
+            case KeyExchangeAlgorithm.DH_DSS:
+            case KeyExchangeAlgorithm.DH_RSA:
+            case KeyExchangeAlgorithm.DHE_DSS:
+            case KeyExchangeAlgorithm.DHE_PSK:
+            case KeyExchangeAlgorithm.DHE_RSA:
+                return true;
+
+            default:
+                return false;
+            }
+        }
+
+        public static int GetNamedGroupForDHParameters(BigInteger p, BigInteger g)
+        {
+            int[] namedGroups = new int[]{ NamedGroup.ffdhe2048, NamedGroup.ffdhe3072, NamedGroup.ffdhe4096,
+                NamedGroup.ffdhe6144, NamedGroup.ffdhe8192 };
+
+            for (int i = 0; i < namedGroups.Length; ++i)
+            {
+                int namedGroup = namedGroups[i];
+                DHGroup dhGroup = GetNamedDHGroup(namedGroup);
+                if (dhGroup != null && dhGroup.P.Equals(p) && dhGroup.G.Equals(g))
+                    return namedGroup;
+            }
+
+            return -1;
+        }
+
+        public static DHGroup GetStandardGroupForDHParameters(BigInteger p, BigInteger g)
+        {
+            DHGroup[] standardGroups = new DHGroup[] { DHStandardGroups.rfc7919_ffdhe2048,
+                DHStandardGroups.rfc7919_ffdhe3072, DHStandardGroups.rfc7919_ffdhe4096, DHStandardGroups.rfc7919_ffdhe6144,
+                DHStandardGroups.rfc7919_ffdhe8192, DHStandardGroups.rfc3526_1536, DHStandardGroups.rfc3526_2048,
+                DHStandardGroups.rfc3526_3072, DHStandardGroups.rfc3526_4096, DHStandardGroups.rfc3526_6144,
+                DHStandardGroups.rfc3526_8192, DHStandardGroups.rfc5996_768, DHStandardGroups.rfc5996_1024 };
+
+            for (int i = 0; i < standardGroups.Length; ++i)
+            {
+                DHGroup dhGroup = standardGroups[i];
+                if (dhGroup != null && dhGroup.P.Equals(p) && dhGroup.G.Equals(g))
+                    return dhGroup;
+            }
+
+            return null;
+        }
+
+        /// <exception cref="IOException"/>
+        public static TlsDHConfig ReceiveDHConfig(TlsContext context, TlsDHGroupVerifier dhGroupVerifier,
+            Stream input)
+        {
+            BigInteger p = ReadDHParameter(input);
+            BigInteger g = ReadDHParameter(input);
+
+            int namedGroup = GetNamedGroupForDHParameters(p, g);
+            if (namedGroup< 0)
+            {
+                DHGroup dhGroup = GetStandardGroupForDHParameters(p, g);
+                if (null == dhGroup)
+                {
+                    dhGroup = new DHGroup(p, null, g, 0);
+                }
+
+                if (!dhGroupVerifier.Accept(dhGroup))
+                    throw new TlsFatalAlert(AlertDescription.insufficient_security);
+
+                return new TlsDHConfig(dhGroup);
+            }
+
+            int[] clientSupportedGroups = context.SecurityParameters.ClientSupportedGroups;
+            if (null == clientSupportedGroups || Arrays.Contains(clientSupportedGroups, namedGroup))
+                return new TlsDHConfig(namedGroup, false);
+
+            throw new TlsFatalAlert(AlertDescription.illegal_parameter);
+        }
+
+        /// <exception cref="IOException"/>
+        public static BigInteger ReadDHParameter(Stream input)
+        {
+            return new BigInteger(1, TlsUtilities.ReadOpaque16(input, 1));
+        }
+
+        /// <exception cref="IOException"/>
+        public static void WriteDHConfig(TlsDHConfig dhConfig, Stream output)
+        {
+            DHGroup group = GetDHGroup(dhConfig);
+            WriteDHParameter(group.P, output);
+            WriteDHParameter(group.G, output);
+        }
+
+        /// <exception cref="IOException"/>
+        public static void WriteDHParameter(BigInteger x, Stream output)
+        {
+            TlsUtilities.WriteOpaque16(BigIntegers.AsUnsignedByteArray(x), output);
+        }
+    }
+}