public RecipientInfo Generate(KeyParameter contentEncryptionKey, SecureRandom random)
{
byte[] keyBytes = contentEncryptionKey.GetKey();
AsymmetricKeyParameter senderPublicKey = senderKeyPair.Public;
ICipherParameters senderPrivateParams = senderKeyPair.Private;
OriginatorIdentifierOrKey originator;
try
{
originator = new OriginatorIdentifierOrKey(
CreateOriginatorPublicKey(senderPublicKey));
}
catch (IOException e)
{
throw new InvalidKeyException("cannot extract originator public key: " + e);
}
Asn1OctetString ukm = null;
if (keyAgreementOID.Id.Equals(CmsEnvelopedGenerator.ECMqvSha1Kdf))
{
try
{
IAsymmetricCipherKeyPairGenerator ephemKPG =
GeneratorUtilities.GetKeyPairGenerator(keyAgreementOID);
ephemKPG.Init(
((ECPublicKeyParameters)senderPublicKey).CreateKeyGenerationParameters(random));
AsymmetricCipherKeyPair ephemKP = ephemKPG.GenerateKeyPair();
ukm = new DerOctetString(
new MQVuserKeyingMaterial(
CreateOriginatorPublicKey(ephemKP.Public), null));
senderPrivateParams = new MqvPrivateParameters(
(ECPrivateKeyParameters)senderPrivateParams,
(ECPrivateKeyParameters)ephemKP.Private,
(ECPublicKeyParameters)ephemKP.Public);
}
catch (IOException e)
{
throw new InvalidKeyException("cannot extract MQV ephemeral public key: " + e);
}
catch (SecurityUtilityException e)
{
throw new InvalidKeyException("cannot determine MQV ephemeral key pair parameters from public key: " + e);
}
}
DerSequence paramSeq = new DerSequence(
keyEncryptionOID,
DerNull.Instance);
AlgorithmIdentifier keyEncAlg = new AlgorithmIdentifier(keyAgreementOID, paramSeq);
Asn1EncodableVector recipientEncryptedKeys = new Asn1EncodableVector();
foreach (X509Certificate recipientCert in recipientCerts)
{
TbsCertificateStructure tbsCert;
try
{
tbsCert = TbsCertificateStructure.GetInstance(
Asn1Object.FromByteArray(recipientCert.GetTbsCertificate()));
}
catch (Exception)
{
throw new ArgumentException("can't extract TBS structure from certificate");
}
// TODO Should there be a SubjectKeyIdentifier-based alternative?
IssuerAndSerialNumber issuerSerial = new IssuerAndSerialNumber(
tbsCert.Issuer, tbsCert.SerialNumber.Value);
KeyAgreeRecipientIdentifier karid = new KeyAgreeRecipientIdentifier(issuerSerial);
ICipherParameters recipientPublicParams = recipientCert.GetPublicKey();
if (keyAgreementOID.Id.Equals(CmsEnvelopedGenerator.ECMqvSha1Kdf))
{
recipientPublicParams = new MqvPublicParameters(
(ECPublicKeyParameters)recipientPublicParams,
(ECPublicKeyParameters)recipientPublicParams);
}
// Use key agreement to choose a wrap key for this recipient
IBasicAgreement keyAgreement = AgreementUtilities.GetBasicAgreementWithKdf(
keyAgreementOID, keyEncryptionOID.Id);
keyAgreement.Init(new ParametersWithRandom(senderPrivateParams, random));
BigInteger agreedValue = keyAgreement.CalculateAgreement(recipientPublicParams);
int keyEncryptionKeySize = GeneratorUtilities.GetDefaultKeySize(keyEncryptionOID) / 8;
byte[] keyEncryptionKeyBytes = X9IntegerConverter.IntegerToBytes(agreedValue, keyEncryptionKeySize);
KeyParameter keyEncryptionKey = ParameterUtilities.CreateKeyParameter(
keyEncryptionOID, keyEncryptionKeyBytes);
// Wrap the content encryption key with the agreement key
IWrapper keyWrapper = Helper.CreateWrapper(keyEncryptionOID.Id);
keyWrapper.Init(true, new ParametersWithRandom(keyEncryptionKey, random));
byte[] encryptedKeyBytes = keyWrapper.Wrap(keyBytes, 0, keyBytes.Length);
Asn1OctetString encryptedKey = new DerOctetString(encryptedKeyBytes);
recipientEncryptedKeys.Add(new RecipientEncryptedKey(karid, encryptedKey));
}
return new RecipientInfo(new KeyAgreeRecipientInfo(originator, ukm, keyEncAlg,
new DerSequence(recipientEncryptedKeys)));
}
private KeyParameter CalculateAgreedWrapKey(
string wrapAlg,
AsymmetricKeyParameter senderPublicKey,
AsymmetricKeyParameter receiverPrivateKey)
{
DerObjectIdentifier agreeAlgID = keyEncAlg.ObjectID;
ICipherParameters senderPublicParams = senderPublicKey;
ICipherParameters receiverPrivateParams = receiverPrivateKey;
if (agreeAlgID.Id.Equals(CmsEnvelopedGenerator.ECMqvSha1Kdf))
{
byte[] ukmEncoding = info.UserKeyingMaterial.GetOctets();
MQVuserKeyingMaterial ukm = MQVuserKeyingMaterial.GetInstance(
Asn1Object.FromByteArray(ukmEncoding));
AsymmetricKeyParameter ephemeralKey = GetPublicKeyFromOriginatorPublicKey(
receiverPrivateKey, ukm.EphemeralPublicKey);
senderPublicParams = new MqvPublicParameters(
(ECPublicKeyParameters)senderPublicParams,
(ECPublicKeyParameters)ephemeralKey);
receiverPrivateParams = new MqvPrivateParameters(
(ECPrivateKeyParameters)receiverPrivateParams,
(ECPrivateKeyParameters)receiverPrivateParams);
}
IBasicAgreement agreement = AgreementUtilities.GetBasicAgreementWithKdf(
agreeAlgID, wrapAlg);
agreement.Init(receiverPrivateParams);
BigInteger agreedValue = agreement.CalculateAgreement(senderPublicParams);
int wrapKeySize = GeneratorUtilities.GetDefaultKeySize(wrapAlg) / 8;
byte[] wrapKeyBytes = X9IntegerConverter.IntegerToBytes(agreedValue, wrapKeySize);
return ParameterUtilities.CreateKeyParameter(wrapAlg, wrapKeyBytes);
}
