public override Jwk WrapKey(Jwk?staticKey, JwtObject header, Span <byte> destination)
{
if (staticKey != null)
{
ThrowHelper.ThrowArgumentException_StaticKeyNotSupported();
}
ReadOnlySpan <byte> bytes = Key.AsSpan();
return(SymmetricJwk.FromSpan(bytes, false));
}
/// <inheritsdoc />
public override bool TryUnwrapKey(ReadOnlySpan <byte> keyBytes, Span <byte> destination, JwtHeader header, out int bytesWritten)
{
if (_disposed)
{
ThrowHelper.ThrowObjectDisposedException(GetType());
}
var epk = header.Epk;
if (epk is null)
{
ThrowHelper.ThrowJwtDescriptorException_HeaderIsRequired(HeaderParameters.EpkUtf8);
}
byte[] secretAppend = BuildSecretAppend(header.Apu, header.Apv);
byte[] exchangeHash;
using (var ephemeralKey = ECDiffieHellman.Create(epk.ExportParameters()))
using (var privateKey = ECDiffieHellman.Create(((ECJwk)Key).ExportParameters(true)))
{
if (ephemeralKey.KeySize != privateKey.KeySize)
{
return(ThrowHelper.TryWriteError(out bytesWritten));
}
exchangeHash = privateKey.DeriveKeyFromHash(ephemeralKey.PublicKey, _hashAlgorithm, _secretPreprend, secretAppend);
}
if (Algorithm.ProduceEncryptionKey)
{
using var key = SymmetricJwk.FromSpan(new ReadOnlySpan <byte>(exchangeHash, 0, _keySizeInBytes), false);
if (key.TryGetKeyUnwrapper(EncryptionAlgorithm, Algorithm.WrappedAlgorithm, out var keyUnwrapper))
{
return(keyUnwrapper.TryUnwrapKey(keyBytes, destination, header, out bytesWritten));
}
else
{
return(ThrowHelper.TryWriteError(out bytesWritten));
}
}
else
{
new ReadOnlySpan <byte>(exchangeHash, 0, _keySizeInBytes).CopyTo(destination);
bytesWritten = destination.Length;
return(true);
}
}
/// <inheritsdoc />
public override SymmetricJwk WrapKey(Jwk?staticKey, JwtHeader header, Span <byte> destination)
{
Debug.Assert(header != null);
var partyUInfo = GetPartyInfo(header, JwtHeaderParameterNames.Apu);
var partyVInfo = GetPartyInfo(header, JwtHeaderParameterNames.Apv);
var secretAppend = BuildSecretAppend(partyUInfo, partyVInfo);
ReadOnlySpan <byte> exchangeHash;
var ecKey = _key;
var otherPartyKey = ecKey.CreateEcdhKey();
ECDiffieHellman ephemeralKey = (staticKey is null) ? ECDiffieHellman.Create(ecKey.Crv.CurveParameters) : ((ECJwk)staticKey).CreateEcdhKey();
try
{
exchangeHash = new ReadOnlySpan <byte>(ephemeralKey.DeriveKeyFromHash(otherPartyKey.PublicKey, _hashAlgorithm, _secretPreprend, secretAppend), 0, _keySizeInBytes);
var epk = ECJwk.FromParameters(ephemeralKey.ExportParameters(false));
header.Add(JwtHeaderParameterNames.Epk, epk);
}
finally
{
if (staticKey is null)
{
ephemeralKey.Dispose();
}
}
SymmetricJwk contentEncryptionKey;
if (Algorithm.ProduceEncryptionKey)
{
using var keyWrapper = new AesKeyWrapper(exchangeHash, EncryptionAlgorithm, _keyManagementAlgorithm !);
contentEncryptionKey = keyWrapper.WrapKey(null, header, destination);
}
else
{
exchangeHash.CopyTo(destination);
contentEncryptionKey = SymmetricJwk.FromSpan(exchangeHash, false);
}
return(contentEncryptionKey);
}
