RSAPkcs1X509SignatureGenerator.cs

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using System.Formats.Asn1;
 
namespace System.Security.Cryptography.X509Certificates;
 
internal sealed class RSAPkcs1X509SignatureGenerator : X509SignatureGenerator
{
    private readonly RSA _key;
 
    internal RSAPkcs1X509SignatureGenerator(RSA key)
    {
        _key = key;
    }
 
    public override byte[] SignData(byte[] data, HashAlgorithmName hashAlgorithm)
    {
        return _key.SignData(data, hashAlgorithm, RSASignaturePadding.Pkcs1);
    }
 
    protected override PublicKey BuildPublicKey()
    {
        return BuildPublicKey(_key);
    }
 
    internal static PublicKey BuildPublicKey(RSA rsa)
    {
        Oid rsaOid = System.Security.Cryptography.Oids.RsaOid;
        Oid oid = rsaOid;
        Oid oid2 = rsaOid;
        Span<byte> span = stackalloc byte[2] { 5, 0 };
        return new PublicKey(oid, new AsnEncodedData(oid2, span), new AsnEncodedData(rsaOid, rsa.ExportRSAPublicKey()));
    }
 
    public override byte[] GetSignatureAlgorithmIdentifier(HashAlgorithmName hashAlgorithm)
    {
        string oidValue;
        if (hashAlgorithm == HashAlgorithmName.SHA256)
        {
            oidValue = "1.2.840.113549.1.1.11";
        }
        else if (hashAlgorithm == HashAlgorithmName.SHA384)
        {
            oidValue = "1.2.840.113549.1.1.12";
        }
        else
        {
            if (!(hashAlgorithm == HashAlgorithmName.SHA512))
            {
                throw new ArgumentOutOfRangeException("hashAlgorithm", hashAlgorithm, System.SR.Format(System.SR.Cryptography_UnknownHashAlgorithm, hashAlgorithm.Name));
            }
            oidValue = "1.2.840.113549.1.1.13";
        }
        AsnWriter asnWriter = new AsnWriter(AsnEncodingRules.DER);
        asnWriter.PushSequence();
        asnWriter.WriteObjectIdentifier(oidValue);
        asnWriter.WriteNull();
        asnWriter.PopSequence();
        return asnWriter.Encode();
    }
}