public override byte[] DeriveKeyFromHmac(
ECDiffieHellmanPublicKey otherPartyPublicKey,
HashAlgorithmName hashAlgorithm,
byte[]?hmacKey,
byte[]?secretPrepend,
byte[]?secretAppend)
{
if (otherPartyPublicKey == null)
{
throw new ArgumentNullException(nameof(otherPartyPublicKey));
}
if (string.IsNullOrEmpty(hashAlgorithm.Name))
{
throw new ArgumentException(SR.Cryptography_HashAlgorithmNameNullOrEmpty, nameof(hashAlgorithm));
}
using (SafeNCryptSecretHandle secretAgreement = DeriveSecretAgreementHandle(otherPartyPublicKey))
{
Interop.NCrypt.SecretAgreementFlags flags = hmacKey == null ?
Interop.NCrypt.SecretAgreementFlags.UseSecretAsHmacKey :
Interop.NCrypt.SecretAgreementFlags.None;
return(Interop.NCrypt.DeriveKeyMaterialHmac(
secretAgreement,
hashAlgorithm.Name,
hmacKey,
secretPrepend,
secretAppend,
flags));
}
}
public byte[] DeriveKeyMaterial(CngKey otherPartyPublicKey)
{
ArgumentNullException.ThrowIfNull(otherPartyPublicKey);
if (otherPartyPublicKey.AlgorithmGroup != CngAlgorithmGroup.ECDiffieHellman)
{
throw new ArgumentException(SR.Cryptography_ArgECDHRequiresECDHKey, nameof(otherPartyPublicKey));
}
if (otherPartyPublicKey.KeySize != KeySize)
{
throw new ArgumentException(SR.Cryptography_ArgECDHKeySizeMismatch, nameof(otherPartyPublicKey));
}
// Setting the flag to UseSecretAsHmacKey even when the KDF isn't HMAC, because that's what .NET Framework does.
Interop.NCrypt.SecretAgreementFlags flags =
UseSecretAgreementAsHmacKey
? Interop.NCrypt.SecretAgreementFlags.UseSecretAsHmacKey
: Interop.NCrypt.SecretAgreementFlags.None;
using (SafeNCryptSecretHandle handle = DeriveSecretAgreementHandle(otherPartyPublicKey))
{
switch (KeyDerivationFunction)
{
case ECDiffieHellmanKeyDerivationFunction.Hash:
return(Interop.NCrypt.DeriveKeyMaterialHash(
handle,
HashAlgorithm.Algorithm,
_secretPrepend,
_secretAppend,
flags));
case ECDiffieHellmanKeyDerivationFunction.Hmac:
return(Interop.NCrypt.DeriveKeyMaterialHmac(
handle,
HashAlgorithm.Algorithm,
_hmacKey,
_secretPrepend,
_secretAppend,
flags));
case ECDiffieHellmanKeyDerivationFunction.Tls:
if (_label == null || _seed == null)
{
throw new InvalidOperationException(SR.Cryptography_TlsRequiresLabelAndSeed);
}
return(Interop.NCrypt.DeriveKeyMaterialTls(
handle,
_label,
_seed,
flags));
default:
Debug.Fail($"Unknown KDF ({KeyDerivationFunction})");
// Match .NET Framework behavior
goto case ECDiffieHellmanKeyDerivationFunction.Tls;
}
}
}
