CurveAsn.cs

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using System.Formats.Asn1;
 
namespace System.Security.Cryptography.Asn1;
 
internal struct CurveAsn
{
    internal ReadOnlyMemory<byte> A;
 
    internal ReadOnlyMemory<byte> B;
 
    internal ReadOnlyMemory<byte>? Seed;
 
    internal void Encode(AsnWriter writer)
    {
        Encode(writer, Asn1Tag.Sequence);
    }
 
    internal void Encode(AsnWriter writer, Asn1Tag tag)
    {
        writer.PushSequence(tag);
        writer.WriteOctetString(A.Span);
        writer.WriteOctetString(B.Span);
        if (Seed.HasValue)
        {
            writer.WriteBitString(Seed.Value.Span);
        }
        writer.PopSequence(tag);
    }
 
    internal static void Decode(ref System.Formats.Asn1.AsnValueReader reader, ReadOnlyMemory<byte> rebind, out System.Security.Cryptography.Asn1.CurveAsn decoded)
    {
        Decode(ref reader, Asn1Tag.Sequence, rebind, out decoded);
    }
 
    internal static void Decode(ref System.Formats.Asn1.AsnValueReader reader, Asn1Tag expectedTag, ReadOnlyMemory<byte> rebind, out System.Security.Cryptography.Asn1.CurveAsn decoded)
    {
        try
        {
            DecodeCore(ref reader, expectedTag, rebind, out decoded);
        }
        catch (AsnContentException inner)
        {
            throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding, inner);
        }
    }
 
    private static void DecodeCore(ref System.Formats.Asn1.AsnValueReader reader, Asn1Tag expectedTag, ReadOnlyMemory<byte> rebind, out System.Security.Cryptography.Asn1.CurveAsn decoded)
    {
        decoded = default(System.Security.Cryptography.Asn1.CurveAsn);
        System.Formats.Asn1.AsnValueReader asnValueReader = reader.ReadSequence(expectedTag);
        ReadOnlySpan<byte> span = rebind.Span;
        int elementOffset;
        if (asnValueReader.TryReadPrimitiveOctetString(out var value))
        {
            decoded.A = (span.Overlaps(value, out elementOffset) ? rebind.Slice(elementOffset, value.Length) : ((ReadOnlyMemory<byte>)value.ToArray()));
        }
        else
        {
            decoded.A = asnValueReader.ReadOctetString();
        }
        if (asnValueReader.TryReadPrimitiveOctetString(out value))
        {
            decoded.B = (span.Overlaps(value, out elementOffset) ? rebind.Slice(elementOffset, value.Length) : ((ReadOnlyMemory<byte>)value.ToArray()));
        }
        else
        {
            decoded.B = asnValueReader.ReadOctetString();
        }
        if (asnValueReader.HasData && asnValueReader.PeekTag().HasSameClassAndValue(Asn1Tag.PrimitiveBitString))
        {
            if (asnValueReader.TryReadPrimitiveBitString(out var unusedBitCount, out value))
            {
                decoded.Seed = (span.Overlaps(value, out elementOffset) ? rebind.Slice(elementOffset, value.Length) : ((ReadOnlyMemory<byte>)value.ToArray()));
            }
            else
            {
                decoded.Seed = asnValueReader.ReadBitString(out unusedBitCount);
            }
        }
        asnValueReader.ThrowIfNotEmpty();
    }
}