// ==++==
// 
//   Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// ==--==
 
using System;
using System.IO;
 
namespace System.Security.Cryptography {
    /// <summary>
    ///     Base class for implementations of elliptic curve DSA
    /// </summary>
    [System.Security.Permissions.HostProtection(MayLeakOnAbort = true)]
    public abstract class ECDsa : AsymmetricAlgorithm {
        public override string KeyExchangeAlgorithm {
            get { return null; }
        }
 
        public override string SignatureAlgorithm {
            get { return "ECDsa"; }
        }
 
        //
        // Creation factory methods
        //
 
        public static new ECDsa Create() {
            return Create(typeof(ECDsaCng).FullName);
        }
 
        public static new ECDsa Create(string algorithm) {
            if (algorithm == null) {
                throw new ArgumentNullException("algorithm");
            }
 
            return CryptoConfig.CreateFromName(algorithm) as ECDsa;
        }
 
        /// <summary>
        /// Creates a new instance of the default implementation of the Elliptic Curve Digital Signature Algorithm
        /// (ECDSA) with a newly generated key over the specified curve.
        /// </summary>
        /// <param name="curve">The curve to use for key generation.</param>
        /// <returns>A new instance of the default implementation of this class.</returns>
        public static ECDsa Create(ECCurve curve) {
            ECDsa ecdsa = Create();
 
            if (ecdsa != null) {
                try {
                    ecdsa.GenerateKey(curve);
                }
                catch {
                    ecdsa.Dispose();
                    throw;
                }
            }
 
            return ecdsa;
        }
 
        /// <summary>
        /// Creates a new instance of the default implementation of the Elliptic Curve Digital Signature Algorithm
        /// (ECDSA) using the specified ECParameters as the key.
        /// </summary>
        /// <param name="parameters">The parameters representing the key to use.</param>
        /// <returns>A new instance of the default implementation of this class.</returns>
        public static ECDsa Create(ECParameters parameters) {
            ECDsa ecdsa = Create();
 
            if (ecdsa != null) {
                try {
                    ecdsa.ImportParameters(parameters);
                }
                catch {
                    ecdsa.Dispose();
                    throw;
                }
            }
 
            return ecdsa;
        }
 
        //
        // Signature operations
        //
 
        // ECDsa does not encode the algorithm identifier into the signature blob, therefore SignHash and VerifyHash
        // do not need the HashAlgorithmName value, only SignData and VerifyData do.
        public abstract byte[] SignHash(byte[] hash);
        public abstract bool VerifyHash(byte[] hash, byte[] signature);
 
        protected virtual byte[] HashData(byte[] data, int offset, int count, HashAlgorithmName hashAlgorithm) {
            throw DerivedClassMustOverride();
        }
 
        protected virtual byte[] HashData(Stream data, HashAlgorithmName hashAlgorithm) {
            throw DerivedClassMustOverride();
        }
 
        public virtual byte[] SignData(byte[] data, HashAlgorithmName hashAlgorithm) {
            if (data == null) {
                throw new ArgumentNullException("data");
            }
            return SignData(data, 0, data.Length, hashAlgorithm);
        }
 
        public virtual byte[] SignData(byte[] data, int offset, int count, HashAlgorithmName hashAlgorithm) {
            if (data == null) { throw new ArgumentNullException("data"); }
            if (offset < 0 || offset > data.Length) { throw new ArgumentOutOfRangeException("offset"); }
            if (count < 0 || count > data.Length - offset) { throw new ArgumentOutOfRangeException("count"); }
            if (String.IsNullOrEmpty(hashAlgorithm.Name)) { throw HashAlgorithmNameNullOrEmpty(); }
 
            byte[] hash = HashData(data, offset, count, hashAlgorithm);
            return SignHash(hash);
        }
 
        public virtual byte[] SignData(Stream data, HashAlgorithmName hashAlgorithm) {
            if (data == null) {
                throw new ArgumentNullException("data");
            }
            if (String.IsNullOrEmpty(hashAlgorithm.Name)) {
                throw HashAlgorithmNameNullOrEmpty();
            }
 
            byte[] hash = HashData(data, hashAlgorithm);
            return SignHash(hash);
        }
 
        public bool VerifyData(byte[] data, byte[] signature, HashAlgorithmName hashAlgorithm) {
            if (data == null) {
                throw new ArgumentNullException("data");
            }
            return VerifyData(data, 0, data.Length, signature, hashAlgorithm);
        }
 
        public virtual bool VerifyData(byte[] data, int offset, int count, byte[] signature, HashAlgorithmName hashAlgorithm) {
            if (data == null) {
                throw new ArgumentNullException("data");
            }
            if (offset < 0 || offset > data.Length) {
                throw new ArgumentOutOfRangeException("offset");
            }
            if (count < 0 || count > data.Length - offset) {
                throw new ArgumentOutOfRangeException("count");
            }
            if (signature == null) {
                throw new ArgumentNullException("signature");
            }
            if (String.IsNullOrEmpty(hashAlgorithm.Name)) {
                throw HashAlgorithmNameNullOrEmpty();
            }
 
            byte[] hash = HashData(data, offset, count, hashAlgorithm);
            return VerifyHash(hash, signature);
        }
 
        public bool VerifyData(Stream data, byte[] signature, HashAlgorithmName hashAlgorithm) {
            if (data == null) {
                throw new ArgumentNullException("data");
            }
            if (signature == null) {
                throw new ArgumentNullException("signature");
            }
            if (String.IsNullOrEmpty(hashAlgorithm.Name)) {
                throw HashAlgorithmNameNullOrEmpty();
            }
 
            byte[] hash = HashData(data, hashAlgorithm);
            return VerifyHash(hash, signature);
        }
 
        /// <summary>
        /// When overridden in a derived class, exports the named or explicit ECParameters for an ECCurve.
        /// If the curve has a name, the Curve property will contain named curve parameters, otherwise it
        /// will contain explicit parameters.
        /// </summary>
        /// <param name="includePrivateParameters">true to include private parameters, otherwise, false.</param>
        /// <returns>The ECParameters representing the point on the curve for this key.</returns>
        public virtual ECParameters ExportParameters(bool includePrivateParameters) {
            throw new NotSupportedException(SR.GetString(SR.NotSupported_SubclassOverride));
        }
 
        /// <summary>
        /// When overridden in a derived class, exports the explicit ECParameters for an ECCurve.
        /// </summary>
        /// <param name="includePrivateParameters">true to include private parameters, otherwise, false.</param>
        /// <returns>The ECParameters representing the point on the curve for this key, using the explicit curve format.</returns>
        public virtual ECParameters ExportExplicitParameters(bool includePrivateParameters) {
            throw new NotSupportedException(SR.GetString(SR.NotSupported_SubclassOverride));
        }
 
        /// <summary>
        /// When overridden in a derived class, imports the specified ECParameters.
        /// </summary>
        /// <param name="parameters">The curve parameters.</param>
        public virtual void ImportParameters(ECParameters parameters) {
            throw new NotSupportedException(SR.GetString(SR.NotSupported_SubclassOverride));
        }
 
        /// <summary>
        /// When overridden in a derived class, generates a new public/private keypair for the specified curve.
        /// </summary>
        /// <param name="curve">The curve to use.</param>
        public virtual void GenerateKey(ECCurve curve) {
            throw new NotSupportedException(SR.GetString(SR.NotSupported_SubclassOverride));
        }
 
        private static Exception DerivedClassMustOverride() {
            return new NotImplementedException(SR.GetString(SR.NotSupported_SubclassOverride));
        }
 
        internal static Exception HashAlgorithmNameNullOrEmpty() {
            return new ArgumentException(SR.GetString(SR.Cryptography_HashAlgorithmNameNullOrEmpty), "hashAlgorithm");
        }
    }
}