UA-.NETStandard/tests/Opc.Ua.Core.TestFramework/NonExportableECDsa.cs

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using System;
using System.Security.Cryptography;

namespace Opc.Ua.Core.TestFramework
{
    /// <summary>
    /// An <see cref="ECDsa"/> implementation that signs and verifies correctly
    /// but refuses to surrender private key material, mirroring a key held in
    /// a TPM, an HSM, a PKCS#11 token or a remote key management service.
    /// </summary>
    /// <remarks>
    /// See <see cref="NonExportableRsa"/> for the rationale. Only
    /// <see cref="ExportParameters"/> needs to reject the request: the base
    /// class funnels <c>ExportECPrivateKey</c>, <c>ExportPkcs8PrivateKey</c>
    /// and their encrypted variants through it.
    /// </remarks>
    public sealed class NonExportableECDsa : ECDsa
    {
        /// <summary>
        /// Initializes a new instance wrapping a freshly generated software key.
        /// </summary>
        /// <param name="curve">
        /// The named curve used to generate the key.
        /// </param>
        public NonExportableECDsa(ECCurve curve)
            : this(Create(curve), ownsKey: true)
        {
        }

        /// <summary>
        /// Initializes a new instance that delegates operations to an existing key.
        /// </summary>
        /// <param name="key">
        /// The key that performs the actual cryptographic operations.
        /// </param>
        /// <param name="ownsKey">
        /// <c>true</c> if disposing this instance should also dispose
        /// <paramref name="key"/>; otherwise <c>false</c>.
        /// </param>
        public NonExportableECDsa(ECDsa key, bool ownsKey = false)
        {
            m_key = key ?? throw new ArgumentNullException(nameof(key));
            m_ownsKey = ownsKey;
            KeySizeValue = key.KeySize;
            LegalKeySizesValue = [new KeySizes(256, 384, 128), new KeySizes(521, 521, 0)];
        }

        /// <summary>
        /// Gets the number of times an export of the private key was attempted.
        /// </summary>
        /// <remarks>
        /// Tests use this to assert that a code path never reaches for private
        /// key material, rather than merely tolerating the failure.
        /// </remarks>
        public int PrivateKeyExportAttempts => m_privateKeyExportAttempts;

        /// <inheritdoc/>
        public override string KeyExchangeAlgorithm => m_key.KeyExchangeAlgorithm!;

        /// <inheritdoc/>
        public override string SignatureAlgorithm => m_key.SignatureAlgorithm;

        /// <inheritdoc/>
        /// <exception cref="CryptographicException">
        /// Thrown when <paramref name="includePrivateParameters"/> is <c>true</c>,
        /// because the private key is not extractable.
        /// </exception>
        public override ECParameters ExportParameters(bool includePrivateParameters)
        {
            if (includePrivateParameters)
            {
                m_privateKeyExportAttempts++;
                throw new CryptographicException(
                    "The private key is not exportable because it is held in hardware.");
            }

            return m_key.ExportParameters(false);
        }

        /// <inheritdoc/>
        /// <exception cref="CryptographicException">
        /// Thrown when <paramref name="includePrivateParameters"/> is <c>true</c>,
        /// because the private key is not extractable.
        /// </exception>
        public override ECParameters ExportExplicitParameters(bool includePrivateParameters)
        {
            if (includePrivateParameters)
            {
                m_privateKeyExportAttempts++;
                throw new CryptographicException(
                    "The private key is not exportable because it is held in hardware.");
            }

            return m_key.ExportExplicitParameters(false);
        }

        /// <inheritdoc/>
        /// <exception cref="NotSupportedException">
        /// Always thrown; key material cannot be injected into hardware this way.
        /// </exception>
        public override void ImportParameters(ECParameters parameters)
        {
            throw new NotSupportedException(
                "Key material cannot be imported into a hardware protected key.");
        }

        /// <inheritdoc/>
        /// <exception cref="NotSupportedException">
        /// Always thrown; hardware keys are generated in the device.
        /// </exception>
        public override void GenerateKey(ECCurve curve)
        {
            throw new NotSupportedException(
                "A hardware protected key must be generated inside the device.");
        }

        /// <inheritdoc/>
        public override byte[] SignHash(byte[] hash)
        {
            return m_key.SignHash(hash);
        }

        /// <inheritdoc/>
        public override bool VerifyHash(byte[] hash, byte[] signature)
        {
            return m_key.VerifyHash(hash, signature);
        }

        /// <inheritdoc/>
        protected override byte[] HashData(
            byte[] data,
            int offset,
            int count,
            HashAlgorithmName hashAlgorithm)
        {
            return NonExportableKeyHash.Compute(data, offset, count, hashAlgorithm);
        }

        /// <inheritdoc/>
        protected override byte[] HashData(
            System.IO.Stream data,
            HashAlgorithmName hashAlgorithm)
        {
            return NonExportableKeyHash.Compute(data, hashAlgorithm);
        }

        /// <inheritdoc/>
        protected override void Dispose(bool disposing)
        {
            if (disposing && m_ownsKey)
            {
                m_key.Dispose();
            }

            base.Dispose(disposing);
        }

        private readonly ECDsa m_key;
        private readonly bool m_ownsKey;
        private int m_privateKeyExportAttempts;
    }
}