public RecipientEncryptedKey(
KeyAgreeRecipientIdentifier id,
Asn1OctetString encryptedKey)
{
this.identifier = id;
this.encryptedKey = encryptedKey;
}
public RecipientEncryptedKey(
KeyAgreeRecipientIdentifier id,
Asn1OctetString encryptedKey)
{
this.identifier = id;
this.encryptedKey = encryptedKey;
}
private RecipientEncryptedKey(
Asn1Sequence seq)
{
identifier = KeyAgreeRecipientIdentifier.GetInstance(seq[0]);
encryptedKey = (Asn1OctetString)seq[1];
}
public RecipientInfo Generate(KeyParameter contentEncryptionKey, SecureRandom random)
{
byte[] keyBytes = contentEncryptionKey.GetKey();
IAsymmetricKeyParameter 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));
IAsymmetricCipherKeyPair 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));
IBigInteger 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)));
}
public static KeyAgreeRecipientIdentifier GetInstance(Asn1TaggedObject obj, bool isExplicit)
{
return(KeyAgreeRecipientIdentifier.GetInstance(Asn1Sequence.GetInstance(obj, isExplicit)));
}
private RecipientEncryptedKey(
Asn1Sequence seq)
{
identifier = KeyAgreeRecipientIdentifier.GetInstance(seq[0]);
encryptedKey = (Asn1OctetString) seq[1];
}
