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using System;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
namespace Org.BouncyCastle.Crypto.Engines
{
/**
* support class for constructing intergrated encryption ciphers
* for doing basic message exchanges on top of key agreement ciphers
*/
public class IesEngine
{
private readonly IBasicAgreement agree;
private readonly IDerivationFunction kdf;
private readonly IMac mac;
private readonly BufferedBlockCipher cipher;
private readonly byte[] macBuf;
private bool forEncryption;
private ICipherParameters privParam, pubParam;
private IesParameters param;
/**
* set up for use with stream mode, where the key derivation function
* is used to provide a stream of bytes to xor with the message.
*
* @param agree the key agreement used as the basis for the encryption
* @param kdf the key derivation function used for byte generation
* @param mac the message authentication code generator for the message
*/
public IesEngine(
IBasicAgreement agree,
IDerivationFunction kdf,
IMac mac)
{
this.agree = agree;
this.kdf = kdf;
this.mac = mac;
this.macBuf = new byte[mac.GetMacSize()];
// this.cipher = null;
}
/**
* set up for use in conjunction with a block cipher to handle the
* message.
*
* @param agree the key agreement used as the basis for the encryption
* @param kdf the key derivation function used for byte generation
* @param mac the message authentication code generator for the message
* @param cipher the cipher to used for encrypting the message
*/
public IesEngine(
IBasicAgreement agree,
IDerivationFunction kdf,
IMac mac,
BufferedBlockCipher cipher)
{
this.agree = agree;
this.kdf = kdf;
this.mac = mac;
this.macBuf = new byte[mac.GetMacSize()];
this.cipher = cipher;
}
/**
* Initialise the encryptor.
*
* @param forEncryption whether or not this is encryption/decryption.
* @param privParam our private key parameters
* @param pubParam the recipient's/sender's public key parameters
* @param param encoding and derivation parameters.
*/
public void Init(
bool forEncryption,
ICipherParameters privParameters,
ICipherParameters pubParameters,
ICipherParameters iesParameters)
{
this.forEncryption = forEncryption;
this.privParam = privParameters;
this.pubParam = pubParameters;
this.param = (IesParameters)iesParameters;
}
private byte[] DecryptBlock(
byte[] in_enc,
int inOff,
int inLen,
byte[] z)
{
byte[] M = null;
KeyParameter macKey = null;
KdfParameters kParam = new KdfParameters(z, param.GetDerivationV());
int macKeySize = param.MacKeySize;
kdf.Init(kParam);
inLen -= mac.GetMacSize();
if (cipher == null) // stream mode
{
byte[] Buffer = GenerateKdfBytes(kParam, inLen + (macKeySize / 8));
M = new byte[inLen];
for (int i = 0; i != inLen; i++)
{
M[i] = (byte)(in_enc[inOff + i] ^ Buffer[i]);
}
macKey = new KeyParameter(Buffer, inLen, (macKeySize / 8));
}
else
{
int cipherKeySize = ((IesWithCipherParameters)param).CipherKeySize;
byte[] Buffer = GenerateKdfBytes(kParam, (cipherKeySize / 8) + (macKeySize / 8));
cipher.Init(false, new KeyParameter(Buffer, 0, (cipherKeySize / 8)));
M = cipher.DoFinal(in_enc, inOff, inLen);
macKey = new KeyParameter(Buffer, (cipherKeySize / 8), (macKeySize / 8));
}
byte[] macIV = param.GetEncodingV();
mac.Init(macKey);
mac.BlockUpdate(in_enc, inOff, inLen);
mac.BlockUpdate(macIV, 0, macIV.Length);
mac.DoFinal(macBuf, 0);
inOff += inLen;
for (int t = 0; t < macBuf.Length; t++)
{
if (macBuf[t] != in_enc[inOff + t])
{
throw (new InvalidCipherTextException("IMac codes failed to equal."));
}
}
return M;
}
private byte[] EncryptBlock(
byte[] input,
int inOff,
int inLen,
byte[] z)
{
byte[] C = null;
KeyParameter macKey = null;
KdfParameters kParam = new KdfParameters(z, param.GetDerivationV());
int c_text_length = 0;
int macKeySize = param.MacKeySize;
if (cipher == null) // stream mode
{
byte[] Buffer = GenerateKdfBytes(kParam, inLen + (macKeySize / 8));
C = new byte[inLen + mac.GetMacSize()];
c_text_length = inLen;
for (int i = 0; i != inLen; i++)
{
C[i] = (byte)(input[inOff + i] ^ Buffer[i]);
}
macKey = new KeyParameter(Buffer, inLen, (macKeySize / 8));
}
else
{
int cipherKeySize = ((IesWithCipherParameters)param).CipherKeySize;
byte[] Buffer = GenerateKdfBytes(kParam, (cipherKeySize / 8) + (macKeySize / 8));
cipher.Init(true, new KeyParameter(Buffer, 0, (cipherKeySize / 8)));
c_text_length = cipher.GetOutputSize(inLen);
byte[] tmp = new byte[c_text_length];
int len = cipher.ProcessBytes(input, inOff, inLen, tmp, 0);
len += cipher.DoFinal(tmp, len);
C = new byte[len + mac.GetMacSize()];
c_text_length = len;
Array.Copy(tmp, 0, C, 0, len);
macKey = new KeyParameter(Buffer, (cipherKeySize / 8), (macKeySize / 8));
}
byte[] macIV = param.GetEncodingV();
mac.Init(macKey);
mac.BlockUpdate(C, 0, c_text_length);
mac.BlockUpdate(macIV, 0, macIV.Length);
//
// return the message and it's MAC
//
mac.DoFinal(C, c_text_length);
return C;
}
private byte[] GenerateKdfBytes(
KdfParameters kParam,
int length)
{
byte[] buf = new byte[length];
kdf.Init(kParam);
kdf.GenerateBytes(buf, 0, buf.Length);
return buf;
}
public byte[] ProcessBlock(
byte[] input,
int inOff,
int inLen)
{
agree.Init(privParam);
BigInteger z = agree.CalculateAgreement(pubParam);
// TODO Is a fixed length result expected?
byte[] zBytes = z.ToByteArrayUnsigned();
return forEncryption
? EncryptBlock(input, inOff, inLen, zBytes)
: DecryptBlock(input, inOff, inLen, zBytes);
}
}
}
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