/// <summary>
/// Gets ASN-encoded algorithm identifier based on current configuration.
/// </summary>
/// <param name="alternate">
/// Specifies whether alternate signature format is used. This parameter has meaning only for
/// ECDSA keys. Otherwise, the parameter is ignored. Default value is <strong>false</strong>.
/// </param>
/// <returns>ASN-encoded algorithm identifier.</returns>
public AlgorithmIdentifier GetAlgorithmIdentifier(Boolean alternate = false)
{
if (SignatureAlgorithm == null)
{
getSignatureAlgorithm();
}
Oid algId = SignatureAlgorithm;
List <Byte> parameters = new List <Byte>();
switch (PublicKeyAlgorithm.Value)
{
case AlgorithmOids.ECC: // ECDSA
if (alternate)
{
// specifiedECDSA
algId = new Oid(AlgorithmOids.ECDSA_SPECIFIED); // only here we override algorithm OID
parameters
.AddRange(
new AlgorithmIdentifier(HashingAlgorithm.ToOid(), Asn1Utils.EncodeNull()).RawData
);
}
break;
case AlgorithmOids.RSA: // RSA
// only RSA supports parameters. For PKCS1 padding: NULL, for PSS padding:
// RSASSA-PSS-params ::= SEQUENCE {
// hashAlgorithm [0] HashAlgorithm DEFAULT sha1,
// maskGenAlgorithm [1] MaskGenAlgorithm DEFAULT mgf1SHA1,
// saltLength [2] INTEGER DEFAULT 20,
// trailerField [3] TrailerField DEFAULT trailerFieldBC
// }
if (PaddingScheme == SignaturePadding.PSS)
{
Byte[] hash = new AlgorithmIdentifier(HashingAlgorithm.ToOid(), null).RawData;
parameters.AddRange(Asn1Utils.Encode(hash, 0xa0));
// mask generation function: mgf1
Byte[] mgf = new AlgorithmIdentifier(new Oid("1.2.840.113549.1.1.8"), hash).RawData;
parameters.AddRange(Asn1Utils.Encode(mgf, 0xa1));
// salt
parameters.AddRange(Asn1Utils.Encode(new Asn1Integer(20).RawData, 0xa2));
// general PSS parameters encode
parameters = new List <Byte>(Asn1Utils.Encode(parameters.ToArray(), 48));
}
else
{
parameters.AddRange(Asn1Utils.EncodeNull());
}
break;
}
return(new AlgorithmIdentifier(algId, parameters.ToArray()));
}