/// <inheritsdoc />
public override bool TryUnwrapKey(ReadOnlySpan <byte> keyBytes, Span <byte> destination, JwtHeaderDocument header, out int bytesWritten)
{
if (!header.TryGetHeaderParameter(JwtHeaderParameterNames.Epk.EncodedUtf8Bytes, out var epk))
{
ThrowHelper.ThrowJwtDescriptorException_HeaderIsRequired(JwtHeaderParameterNames.Epk);
}
header.TryGetHeaderParameter(JwtHeaderParameterNames.Apu.EncodedUtf8Bytes, out JwtElement apu);
header.TryGetHeaderParameter(JwtHeaderParameterNames.Apv.EncodedUtf8Bytes, out JwtElement apv);
byte[] secretAppend = BuildSecretAppend(apu, apv);
ReadOnlySpan <byte> exchangeHash;
using (var ephemeralKey = ECDiffieHellman.Create(ECJwk.FromJwtElement(epk).ExportParameters()))
{
var privateKey = _key.CreateEcdhKey();
if (ephemeralKey.KeySize != privateKey.KeySize)
{
return(ThrowHelper.TryWriteError(out bytesWritten));
}
exchangeHash = new ReadOnlySpan <byte>(privateKey.DeriveKeyFromHash(ephemeralKey.PublicKey, _hashAlgorithm, _secretPreprend, secretAppend), 0, _keySizeInBytes);
}
if (Algorithm.ProduceEncryptionKey)
{
using var keyUnwrapper = new AesKeyUnwrapper(exchangeHash, EncryptionAlgorithm, _keyManagementAlgorithm !);
return(keyUnwrapper.TryUnwrapKey(keyBytes, destination, header, out bytesWritten));
}
else
{
exchangeHash.CopyTo(destination);
bytesWritten = destination.Length;
return(true);
}
}