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The Long Term Stable (LTS) Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains the JCA/JCE provider and low-level API for the BC LTS version 2.73.7 for Java 8 and later.
package org.bouncycastle.crypto.encodings;
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.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.
*/
public class PKCS1Encoding
implements AsymmetricBlockCipher
{
/**
* old property name - use NOT_STRICT_LENGTH_ENABLED_PROPERTY
*/
private static final String STRICT_LENGTH_ENABLED_PROPERTY = "org.bouncycastle.pkcs1.strict";
/**
* some providers fail to include the leading zero in PKCS1 encoded blocks. If you need to
* work with one of these set the system property org.bouncycastle.pkcs1.not_strict to true.
*
* The system property is checked during construction of the encoding object, it is set to
* false by default.
*
*/
public static final String NOT_STRICT_LENGTH_ENABLED_PROPERTY = "org.bouncycastle.pkcs1.not_strict";
private static final int HEADER_LENGTH = 10;
private SecureRandom random;
private AsymmetricBlockCipher engine;
private boolean forEncryption;
private boolean forPrivateKey;
private boolean useStrictLength;
private int pLen = -1;
private byte[] fallback = null;
private byte[] blockBuffer;
/**
* Basic constructor.
*
* @param cipher
*/
public PKCS1Encoding(
AsymmetricBlockCipher cipher)
{
this.engine = cipher;
this.useStrictLength = useStrict();
}
/**
* Constructor for decryption with a fixed plaintext length.
*
* @param cipher The cipher to use for cryptographic operation.
* @param pLen Length of the expected plaintext.
*/
public PKCS1Encoding(
AsymmetricBlockCipher cipher,
int pLen)
{
this.engine = cipher;
this.useStrictLength = useStrict();
this.pLen = pLen;
}
/**
* Constructor for decryption with a fixed plaintext length and a fallback
* value that is returned, if the padding is incorrect.
*
* @param cipher The cipher to use for cryptographic operation.
* @param fallback The fallback value, we don't do an arraycopy here.
*/
public PKCS1Encoding(
AsymmetricBlockCipher cipher,
byte[] fallback)
{
this.engine = cipher;
this.useStrictLength = useStrict();
this.fallback = fallback;
this.pLen = fallback.length;
}
//
// for J2ME compatibility
//
private boolean useStrict()
{
if (Properties.isOverrideSetTo(NOT_STRICT_LENGTH_ENABLED_PROPERTY, true))
{
return false;
}
return !Properties.isOverrideSetTo(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()];
if (pLen > 0 && fallback == null && random == null)
{
throw new IllegalArgumentException("encoder requires random");
}
}
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);
}
/**
* Checks if the argument is a correctly PKCS#1.5 encoded Plaintext
* for encryption.
*
* @param encoded The Plaintext.
* @param pLen Expected length of the plaintext.
* @return Either 0, if the encoding is correct, or -1, if it is incorrect.
*/
private static int checkPkcs1Encoding(byte[] encoded, int pLen)
{
int correct = 0;
/*
* Check if the first two bytes are 0 2
*/
correct |= (encoded[0] ^ 2);
/*
* Now the padding check, check for no 0 byte in the padding
*/
int plen = encoded.length - (
pLen /* Length of the PMS */
+ 1 /* Final 0-byte before PMS */
);
for (int i = 1; i < plen; i++)
{
int tmp = encoded[i];
tmp |= tmp >> 1;
tmp |= tmp >> 2;
tmp |= tmp >> 4;
correct |= (tmp & 1) - 1;
}
/*
* Make sure the padding ends with a 0 byte.
*/
correct |= encoded[encoded.length - (pLen + 1)];
/*
* Return 0 or 1, depending on the result.
*/
correct |= correct >> 1;
correct |= correct >> 2;
correct |= correct >> 4;
return ~((correct & 1) - 1);
}
/**
* Decode PKCS#1.5 encoding, and return a random value if the padding is not correct.
*
* @param in The encrypted block.
* @param inOff Offset in the encrypted block.
* @param inLen Length of the encrypted block.
* //@param pLen Length of the desired output.
* @return The plaintext without padding, or a random value if the padding was incorrect.
* @throws InvalidCipherTextException
*/
private byte[] decodeBlockOrRandom(byte[] in, int inOff, int inLen)
throws InvalidCipherTextException
{
if (!forPrivateKey)
{
throw new InvalidCipherTextException("sorry, this method is only for decryption, not for signing");
}
byte[] block = engine.processBlock(in, inOff, inLen);
byte[] random;
if (this.fallback == null)
{
random = new byte[this.pLen];
this.random.nextBytes(random);
}
else
{
random = fallback;
}
byte[] data = (useStrictLength & (block.length != engine.getOutputBlockSize())) ? blockBuffer : block;
/*
* Check the padding.
*/
int correct = PKCS1Encoding.checkPkcs1Encoding(data, this.pLen);
/*
* Now, to a constant time constant memory copy of the decrypted value
* or the random value, depending on the validity of the padding.
*/
byte[] result = new byte[this.pLen];
for (int i = 0; i < this.pLen; i++)
{
result[i] = (byte)((data[i + (data.length - pLen)] & (~correct)) | (random[i] & correct));
}
Arrays.fill(data, (byte)0);
return result;
}
/**
* @throws InvalidCipherTextException if the decrypted block is not in PKCS1 format.
*/
private byte[] decodeBlock(
byte[] in,
int inOff,
int inLen)
throws InvalidCipherTextException
{
/*
* If the length of the expected plaintext is known, we use a constant-time decryption.
* If the decryption fails, we return a random value.
*/
if (this.pLen != -1)
{
return this.decodeBlockOrRandom(in, inOff, inLen);
}
byte[] block = engine.processBlock(in, inOff, inLen);
boolean incorrectLength = (useStrictLength & (block.length != engine.getOutputBlockSize()));
byte[] data;
if (block.length < getOutputBlockSize())
{
data = blockBuffer;
}
else
{
data = block;
}
byte type = data[0];
boolean badType;
if (forPrivateKey)
{
badType = (type != 2);
}
else
{
badType = (type != 1);
}
//
// find and extract the message block.
//
int start = findStart(type, data);
start++; // data should start at the next byte
if (badType | start < HEADER_LENGTH)
{
Arrays.fill(data, (byte)0);
throw new InvalidCipherTextException("block incorrect");
}
// if we get this far, it's likely to be a genuine encoding error
if (incorrectLength)
{
Arrays.fill(data, (byte)0);
throw new InvalidCipherTextException("block incorrect size");
}
byte[] result = new byte[data.length - start];
System.arraycopy(data, start, result, 0, result.length);
return result;
}
private int findStart(byte type, byte[] block)
throws InvalidCipherTextException
{
int start = -1;
boolean padErr = false;
for (int i = 1; i != block.length; i++)
{
byte pad = block[i];
if (pad == 0 & start < 0)
{
start = i;
}
padErr |= (type == 1 & start < 0 & pad != (byte)0xff);
}
if (padErr)
{
return -1;
}
return start;
}
}
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