DSAKeyFormatHelper.cs

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using System.Formats.Asn1;
using System.Numerics;
using System.Security.Cryptography.Asn1;
 
namespace System.Security.Cryptography;
 
internal static class DSAKeyFormatHelper
{
    private static readonly string[] s_validOids = new string[1] { "1.2.840.10040.4.1" };
 
    internal static void ReadDsaPrivateKey(ReadOnlyMemory<byte> xBytes, in AlgorithmIdentifierAsn algId, out DSAParameters ret)
    {
        if (!algId.Parameters.HasValue)
        {
            throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding);
        }
        DssParms dssParms = DssParms.Decode(algId.Parameters.Value, AsnEncodingRules.BER);
        ret = new DSAParameters
        {
            P = dssParms.P.ToByteArray(isUnsigned: true, isBigEndian: true),
            Q = dssParms.Q.ToByteArray(isUnsigned: true, isBigEndian: true)
        };
        ret.G = dssParms.G.ExportKeyParameter(ret.P.Length);
        BigInteger bigInteger;
        try
        {
            int bytesConsumed;
            ReadOnlySpan<byte> value = AsnDecoder.ReadIntegerBytes(xBytes.Span, AsnEncodingRules.DER, out bytesConsumed);
            if (bytesConsumed != xBytes.Length)
            {
                throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding);
            }
            bigInteger = new BigInteger(value, isUnsigned: true, isBigEndian: true);
        }
        catch (AsnContentException inner)
        {
            throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding, inner);
        }
        ret.X = bigInteger.ExportKeyParameter(ret.Q.Length);
        BigInteger value2 = BigInteger.ModPow(dssParms.G, bigInteger, dssParms.P);
        ret.Y = value2.ExportKeyParameter(ret.P.Length);
    }
 
    internal static void ReadDsaPublicKey(ReadOnlyMemory<byte> yBytes, in AlgorithmIdentifierAsn algId, out DSAParameters ret)
    {
        BigInteger value;
        try
        {
            value = AsnDecoder.ReadInteger(yBytes.Span, AsnEncodingRules.DER, out var bytesConsumed);
            if (bytesConsumed != yBytes.Length)
            {
                throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding);
            }
        }
        catch (AsnContentException inner)
        {
            throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding, inner);
        }
        if (!algId.Parameters.HasValue)
        {
            throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding);
        }
        DssParms dssParms = DssParms.Decode(algId.Parameters.Value, AsnEncodingRules.BER);
        ret = new DSAParameters
        {
            P = dssParms.P.ToByteArray(isUnsigned: true, isBigEndian: true),
            Q = dssParms.Q.ToByteArray(isUnsigned: true, isBigEndian: true)
        };
        ret.G = dssParms.G.ExportKeyParameter(ret.P.Length);
        ret.Y = value.ExportKeyParameter(ret.P.Length);
    }
 
    internal static void ReadSubjectPublicKeyInfo(ReadOnlySpan<byte> source, out int bytesRead, out DSAParameters key)
    {
        KeyFormatHelper.ReadSubjectPublicKeyInfo(s_validOids, source, (KeyFormatHelper.KeyReader<DSAParameters>)ReadDsaPublicKey, out bytesRead, out key);
    }
 
    internal static void ReadPkcs8(ReadOnlySpan<byte> source, out int bytesRead, out DSAParameters key)
    {
        KeyFormatHelper.ReadPkcs8(s_validOids, source, (KeyFormatHelper.KeyReader<DSAParameters>)ReadDsaPrivateKey, out bytesRead, out key);
    }
 
    internal static void ReadEncryptedPkcs8(ReadOnlySpan<byte> source, ReadOnlySpan<char> password, out int bytesRead, out DSAParameters key)
    {
        KeyFormatHelper.ReadEncryptedPkcs8(s_validOids, source, password, (KeyFormatHelper.KeyReader<DSAParameters>)ReadDsaPrivateKey, out bytesRead, out key);
    }
 
    internal static void ReadEncryptedPkcs8(ReadOnlySpan<byte> source, ReadOnlySpan<byte> passwordBytes, out int bytesRead, out DSAParameters key)
    {
        KeyFormatHelper.ReadEncryptedPkcs8(s_validOids, source, passwordBytes, (KeyFormatHelper.KeyReader<DSAParameters>)ReadDsaPrivateKey, out bytesRead, out key);
    }
 
    internal static AsnWriter WriteSubjectPublicKeyInfo(in DSAParameters dsaParameters)
    {
        AsnWriter asnWriter = new AsnWriter(AsnEncodingRules.DER);
        asnWriter.PushSequence();
        WriteAlgorithmId(asnWriter, in dsaParameters);
        WriteKeyComponent(asnWriter, dsaParameters.Y, bitString: true);
        asnWriter.PopSequence();
        return asnWriter;
    }
 
    internal static AsnWriter WritePkcs8(in DSAParameters dsaParameters)
    {
        AsnWriter asnWriter = new AsnWriter(AsnEncodingRules.DER);
        asnWriter.PushSequence();
        asnWriter.WriteInteger(0L);
        WriteAlgorithmId(asnWriter, in dsaParameters);
        WriteKeyComponent(asnWriter, dsaParameters.X, bitString: false);
        asnWriter.PopSequence();
        return asnWriter;
    }
 
    private static void WriteAlgorithmId(AsnWriter writer, in DSAParameters dsaParameters)
    {
        writer.PushSequence();
        writer.WriteObjectIdentifier("1.2.840.10040.4.1");
        writer.PushSequence();
        writer.WriteKeyParameterInteger(dsaParameters.P);
        writer.WriteKeyParameterInteger(dsaParameters.Q);
        writer.WriteKeyParameterInteger(dsaParameters.G);
        writer.PopSequence();
        writer.PopSequence();
    }
 
    private static void WriteKeyComponent(AsnWriter writer, byte[] component, bool bitString)
    {
        if (bitString)
        {
            AsnWriter asnWriter = new AsnWriter(AsnEncodingRules.DER);
            asnWriter.WriteKeyParameterInteger(component);
            byte[] array = System.Security.Cryptography.CryptoPool.Rent(asnWriter.GetEncodedLength());
            if (!asnWriter.TryEncode(array, out var bytesWritten))
            {
                throw new CryptographicException();
            }
            writer.WriteBitString(array.AsSpan(0, bytesWritten));
            System.Security.Cryptography.CryptoPool.Return(array, bytesWritten);
            return;
        }
        using (writer.PushOctetString())
        {
            writer.WriteKeyParameterInteger(component);
        }
    }
}