added missing interface

crypto/src/crypto/IKeyUnwrapper.cs

@@ -0,0 +1,24 @@
+namespace Org.BouncyCastle.Crypto
+{
+    /// <summary>
+    /// Base interface for a key unwrapper.
+    /// </summary>
+    /// <typeparam name="A">The algorithm details/parameter type for the key unwrapper.</typeparam>
+    public interface IKeyUnwrapper<out A>
+	{
+        /// <summary>
+        /// The parameter set used to configure this key unwrapper.
+        /// </summary>
+        A AlgorithmDetails { get; }
+
+        /// <summary>
+        /// Unwrap the passed in data.
+        /// </summary>
+        /// <param name="cipherText">The array containing the data to be unwrapped.</param>
+        /// <param name="offset">The offset into cipherText at which the unwrapped data starts.</param>
+        /// <param name="length">The length of the data to be unwrapped.</param>
+        /// <returns>an IBlockResult containing the unwrapped key data.</returns>
+        IBlockResult Unwrap(byte[] cipherText, int offset, int length);
+	}
+}
+