ECDiffieHellman.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics.CodeAnalysis;
using System.Runtime.Versioning;
using Internal.Cryptography;

namespace System.Security.Cryptography
{
    /// <summary>
    ///     Abstract base class for implementations of elliptic curve Diffie-Hellman to derive from
    /// </summary>
    public abstract partial class ECDiffieHellman : ECAlgorithm
    {
        public override string KeyExchangeAlgorithm
        {
            get { return "ECDiffieHellman"; }
        }

        public override string? SignatureAlgorithm
        {
            get { return null; }
        }

        [UnsupportedOSPlatform("browser")]
        public static new partial ECDiffieHellman Create();

        [UnsupportedOSPlatform("browser")]
        public static partial ECDiffieHellman Create(ECCurve curve);

        [UnsupportedOSPlatform("browser")]
        public static partial ECDiffieHellman Create(ECParameters parameters);

        [Obsolete(Obsoletions.CryptoStringFactoryMessage, DiagnosticId = Obsoletions.CryptoStringFactoryDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
        [RequiresUnreferencedCode(CryptoConfig.CreateFromNameUnreferencedCodeMessage)]
        public static new ECDiffieHellman? Create(string algorithm)
        {
            ArgumentNullException.ThrowIfNull(algorithm);

            return CryptoConfig.CreateFromName(algorithm) as ECDiffieHellman;
        }

        public abstract ECDiffieHellmanPublicKey PublicKey { get; }

        // This method must be implemented by derived classes. In order to conform to the contract, it cannot be abstract.
        public virtual byte[] DeriveKeyMaterial(ECDiffieHellmanPublicKey otherPartyPublicKey)
        {
            throw DerivedClassMustOverride();
        }

        /// <summary>
        /// Derive key material using the formula HASH(x) where x is the computed result of the EC Diffie-Hellman algorithm.
        /// </summary>
        /// <param name="otherPartyPublicKey">The public key of the party with which to derive a mutual secret.</param>
        /// <param name="hashAlgorithm">The identifier for the hash algorithm to use.</param>
        /// <returns>A hashed output suitable for key material</returns>
        /// <exception cref="ArgumentException"><paramref name="otherPartyPublicKey"/> is over a different curve than this key</exception>
        public byte[] DeriveKeyFromHash(ECDiffieHellmanPublicKey otherPartyPublicKey, HashAlgorithmName hashAlgorithm)
        {
            return DeriveKeyFromHash(otherPartyPublicKey, hashAlgorithm, null, null);
        }

        /// <summary>
        /// Derive key material using the formula HASH(secretPrepend || x || secretAppend) where x is the computed
        /// result of the EC Diffie-Hellman algorithm.
        /// </summary>
        /// <param name="otherPartyPublicKey">The public key of the party with which to derive a mutual secret.</param>
        /// <param name="hashAlgorithm">The identifier for the hash algorithm to use.</param>
        /// <param name="secretPrepend">A value to prepend to the derived secret before hashing. A <c>null</c> value is treated as an empty array.</param>
        /// <param name="secretAppend">A value to append to the derived secret before hashing. A <c>null</c> value is treated as an empty array.</param>
        /// <returns>A hashed output suitable for key material</returns>
        /// <exception cref="ArgumentException"><paramref name="otherPartyPublicKey"/> is over a different curve than this key</exception>
        public virtual byte[] DeriveKeyFromHash(
            ECDiffieHellmanPublicKey otherPartyPublicKey,
            HashAlgorithmName hashAlgorithm,
            byte[]? secretPrepend,
            byte[]? secretAppend)
        {
            throw DerivedClassMustOverride();
        }

        /// <summary>
        /// Derive key material using the formula HMAC(hmacKey, x) where x is the computed
        /// result of the EC Diffie-Hellman algorithm.
        /// </summary>
        /// <param name="otherPartyPublicKey">The public key of the party with which to derive a mutual secret.</param>
        /// <param name="hashAlgorithm">The identifier for the hash algorithm to use.</param>
        /// <param name="hmacKey">The key to use in the HMAC. A <c>null</c> value indicates that the result of the EC Diffie-Hellman algorithm should be used as the HMAC key.</param>
        /// <returns>A hashed output suitable for key material</returns>
        /// <exception cref="ArgumentException"><paramref name="otherPartyPublicKey"/> is over a different curve than this key</exception>
        public byte[] DeriveKeyFromHmac(
            ECDiffieHellmanPublicKey otherPartyPublicKey,
            HashAlgorithmName hashAlgorithm,
            byte[]? hmacKey)
        {
            return DeriveKeyFromHmac(otherPartyPublicKey, hashAlgorithm, hmacKey, null, null);
        }

        /// <summary>
        /// Derive key material using the formula HMAC(hmacKey, secretPrepend || x || secretAppend) where x is the computed
        /// result of the EC Diffie-Hellman algorithm.
        /// </summary>
        /// <param name="otherPartyPublicKey">The public key of the party with which to derive a mutual secret.</param>
        /// <param name="hashAlgorithm">The identifier for the hash algorithm to use.</param>
        /// <param name="hmacKey">The key to use in the HMAC. A <c>null</c> value indicates that the result of the EC Diffie-Hellman algorithm should be used as the HMAC key.</param>
        /// <param name="secretPrepend">A value to prepend to the derived secret before hashing. A <c>null</c> value is treated as an empty array.</param>
        /// <param name="secretAppend">A value to append to the derived secret before hashing. A <c>null</c> value is treated as an empty array.</param>
        /// <returns>A hashed output suitable for key material</returns>
        /// <exception cref="ArgumentException"><paramref name="otherPartyPublicKey"/> is over a different curve than this key</exception>
        public virtual byte[] DeriveKeyFromHmac(
            ECDiffieHellmanPublicKey otherPartyPublicKey,
            HashAlgorithmName hashAlgorithm,
            byte[]? hmacKey,
            byte[]? secretPrepend,
            byte[]? secretAppend)
        {
            throw DerivedClassMustOverride();
        }

        /// <summary>
        /// Derive key material using the TLS pseudo-random function (PRF) derivation algorithm.
        /// </summary>
        /// <param name="otherPartyPublicKey">The public key of the party with which to derive a mutual secret.</param>
        /// <param name="prfLabel">The ASCII encoded PRF label.</param>
        /// <param name="prfSeed">The 64-byte PRF seed.</param>
        /// <returns>A 48-byte output of the TLS pseudo-random function.</returns>
        /// <exception cref="ArgumentException"><paramref name="otherPartyPublicKey"/> is over a different curve than this key</exception>
        /// <exception cref="ArgumentNullException"><paramref name="prfLabel"/> is null</exception>
        /// <exception cref="ArgumentNullException"><paramref name="prfSeed"/> is null</exception>
        /// <exception cref="CryptographicException"><paramref name="prfSeed"/> is not exactly 64 bytes in length</exception>
        public virtual byte[] DeriveKeyTls(ECDiffieHellmanPublicKey otherPartyPublicKey, byte[] prfLabel, byte[] prfSeed)
        {
            throw DerivedClassMustOverride();
        }

        private static Exception DerivedClassMustOverride()
        {
            return new NotImplementedException(SR.NotSupported_SubclassOverride);
        }
    }
}