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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.8 and up.
package org.bouncycastle.jcajce.provider.asymmetric.rsa;
import java.security.SecureRandom;
import org.bouncycastle.crypto.AsymmetricBlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.CryptoServicesRegistrar;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.encodings.PKCS1Encoding;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.Properties;
/**
* this does your basic PKCS 1 v1.5 padding - whether or not you should be using this
* depends on your application - see PKCS1 Version 2 for details.
*/
class CustomPKCS1Encoding
implements AsymmetricBlockCipher
{
private static final int HEADER_LENGTH = 10;
private SecureRandom random;
private AsymmetricBlockCipher engine;
private boolean forEncryption;
private boolean forPrivateKey;
private boolean useStrictLength;
private byte[] blockBuffer;
/**
* Basic constructor.
*
* @param cipher
*/
CustomPKCS1Encoding(AsymmetricBlockCipher cipher)
{
this.engine = cipher;
this.useStrictLength = useStrict();
}
//
// for J2ME compatibility
//
private boolean useStrict()
{
if (Properties.isOverrideSetTo(PKCS1Encoding.NOT_STRICT_LENGTH_ENABLED_PROPERTY, true))
{
return false;
}
return !Properties.isOverrideSetTo(PKCS1Encoding.STRICT_LENGTH_ENABLED_PROPERTY, false);
}
public AsymmetricBlockCipher getUnderlyingCipher()
{
return engine;
}
public void init(boolean forEncryption, CipherParameters param)
{
AsymmetricKeyParameter kParam;
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
this.random = rParam.getRandom();
kParam = (AsymmetricKeyParameter)rParam.getParameters();
}
else
{
kParam = (AsymmetricKeyParameter)param;
if (!kParam.isPrivate() && forEncryption)
{
this.random = CryptoServicesRegistrar.getSecureRandom();
}
}
engine.init(forEncryption, param);
this.forPrivateKey = kParam.isPrivate();
this.forEncryption = forEncryption;
this.blockBuffer = new byte[engine.getOutputBlockSize()];
}
public int getInputBlockSize()
{
int baseBlockSize = engine.getInputBlockSize();
if (forEncryption)
{
return baseBlockSize - HEADER_LENGTH;
}
else
{
return baseBlockSize;
}
}
public int getOutputBlockSize()
{
int baseBlockSize = engine.getOutputBlockSize();
if (forEncryption)
{
return baseBlockSize;
}
else
{
return baseBlockSize - HEADER_LENGTH;
}
}
public byte[] processBlock(byte[] in, int inOff, int inLen) throws InvalidCipherTextException
{
if (forEncryption)
{
return encodeBlock(in, inOff, inLen);
}
else
{
return decodeBlock(in, inOff, inLen);
}
}
private byte[] encodeBlock(byte[] in, int inOff, int inLen) throws InvalidCipherTextException
{
if (inLen > getInputBlockSize())
{
throw new IllegalArgumentException("input data too large");
}
byte[] block = new byte[engine.getInputBlockSize()];
if (forPrivateKey)
{
block[0] = 0x01; // type code 1
for (int i = 1; i != block.length - inLen - 1; i++)
{
block[i] = (byte)0xFF;
}
}
else
{
random.nextBytes(block); // random fill
block[0] = 0x02; // type code 2
//
// a zero byte marks the end of the padding, so all
// the pad bytes must be non-zero.
//
for (int i = 1; i != block.length - inLen - 1; i++)
{
while (block[i] == 0)
{
block[i] = (byte)random.nextInt();
}
}
}
block[block.length - inLen - 1] = 0x00; // mark the end of the padding
System.arraycopy(in, inOff, block, block.length - inLen, inLen);
return engine.processBlock(block, 0, block.length);
}
/**
* Check the argument is a valid encoding with type 1. Returns the plaintext length if valid, or -1 if invalid.
*/
private static int checkPkcs1Encoding1(byte[] buf)
{
int foundZeroMask = 0;
int lastPadPos = 0;
// The first byte should be 0x01
int badPadSign = -((buf[0] & 0xFF) ^ 0x01);
// There must be a zero terminator for the padding somewhere
for (int i = 1; i < buf.length; ++i)
{
int padByte = buf[i] & 0xFF;
int is0x00Mask = ((padByte ^ 0x00) - 1) >> 31;
int is0xFFMask = ((padByte ^ 0xFF) - 1) >> 31;
lastPadPos ^= i & ~foundZeroMask & is0x00Mask;
foundZeroMask |= is0x00Mask;
badPadSign |= ~(foundZeroMask | is0xFFMask);
}
// The header should be at least 10 bytes
badPadSign |= lastPadPos - 9;
int plaintextLength = buf.length - 1 - lastPadPos;
return plaintextLength | badPadSign >> 31;
}
/**
* Check the argument is a valid encoding with type 2. Returns the plaintext length if valid, or -1 if invalid.
*/
private static int checkPkcs1Encoding2(byte[] buf)
{
int foundZeroMask = 0;
int lastPadPos = 0;
// The first byte should be 0x02
int badPadSign = -((buf[0] & 0xFF) ^ 0x02);
// There must be a zero terminator for the padding somewhere
for (int i = 1; i < buf.length; ++i)
{
int padByte = buf[i] & 0xFF;
int is0x00Mask = ((padByte ^ 0x00) - 1) >> 31;
lastPadPos ^= i & ~foundZeroMask & is0x00Mask;
foundZeroMask |= is0x00Mask;
}
// The header should be at least 10 bytes
badPadSign |= lastPadPos - 9;
int plaintextLength = buf.length - 1 - lastPadPos;
return plaintextLength | badPadSign >> 31;
}
/**
* @throws InvalidCipherTextException if the decrypted block is not in PKCS1 format.
*/
private byte[] decodeBlock(byte[] in, int inOff, int inLen)
throws InvalidCipherTextException
{
int strictBlockSize = engine.getOutputBlockSize();
byte[] block = engine.processBlock(in, inOff, inLen);
boolean incorrectLength = useStrictLength & (block.length != strictBlockSize);
byte[] data = block;
if (block.length < strictBlockSize)
{
data = blockBuffer;
}
int plaintextLength = forPrivateKey ? checkPkcs1Encoding2(data) : checkPkcs1Encoding1(data);
try
{
if (plaintextLength < 0 | incorrectLength)
{
// Special behaviour to avoid throw/catch/throw in CipherSpi
return null;
}
byte[] result = new byte[plaintextLength];
System.arraycopy(data, data.length - plaintextLength, result, 0, plaintextLength);
return result;
}
finally
{
Arrays.fill(block, (byte)0);
Arrays.fill(blockBuffer, 0, Math.max(0, blockBuffer.length - block.length), (byte)0);
}
}
}