KeyBlobHelpers.cs

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using System.Formats.Asn1;
using System.Numerics;
 
namespace System.Security.Cryptography;
 
internal static class KeyBlobHelpers
{
    internal static byte[] ToUnsignedIntegerBytes(this ReadOnlyMemory<byte> memory, int length)
    {
        if (memory.Length == length)
        {
            return memory.ToArray();
        }
        ReadOnlySpan<byte> span = memory.Span;
        if (memory.Length == length + 1 && span[0] == 0)
        {
            return span.Slice(1).ToArray();
        }
        if (span.Length > length)
        {
            throw new CryptographicException(System.SR.Cryptography_Der_Invalid_Encoding);
        }
        byte[] array = new byte[length];
        span.CopyTo(array.AsSpan(length - span.Length));
        return array;
    }
 
    internal static byte[] ToUnsignedIntegerBytes(this ReadOnlyMemory<byte> memory)
    {
        ReadOnlySpan<byte> span = memory.Span;
        if (span.Length > 1 && span[0] == 0)
        {
            return span.Slice(1).ToArray();
        }
        return span.ToArray();
    }
 
    internal static byte[] ExportKeyParameter(this BigInteger value, int length)
    {
        byte[] array = new byte[length];
        if (value.TryWriteBytes(array, out var bytesWritten, isUnsigned: true, isBigEndian: true))
        {
            if (bytesWritten < length)
            {
                Buffer.BlockCopy(array, 0, array, length - bytesWritten, bytesWritten);
                array.AsSpan(0, length - bytesWritten).Clear();
            }
            return array;
        }
        throw new CryptographicException(System.SR.Cryptography_NotValidPublicOrPrivateKey);
    }
 
    internal static void WriteKeyParameterInteger(this AsnWriter writer, ReadOnlySpan<byte> integer)
    {
        if (integer[0] == 0)
        {
            int i;
            for (i = 1; i < integer.Length; i++)
            {
                if (integer[i] >= 128)
                {
                    i--;
                    break;
                }
                if (integer[i] != 0)
                {
                    break;
                }
            }
            if (i == integer.Length)
            {
                i--;
            }
            integer = integer.Slice(i);
        }
        writer.WriteIntegerUnsigned(integer);
    }
}