package org.bouncycastle.crypto.encodings;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.SecureRandom;
import org.bouncycastle.crypto.AsymmetricBlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
import org.bouncycastle.crypto.params.ParametersWithRandom;
/**
* 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
{
/**
* 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.strict to false.
* <p>
* The system property is checked during construction of the encoding object, it is set to
* true by default.
* </p>
*/
public static final String STRICT_LENGTH_ENABLED_PROPERTY = "org.bouncycastle.pkcs1.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;
/**
* 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()
{
// required if security manager has been installed.
String strict = (String)AccessController.doPrivileged(new PrivilegedAction()
{
public Object run()
{
return System.getProperty(STRICT_LENGTH_ENABLED_PROPERTY);
}
});
return strict == null || strict.equals("true");
}
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
{
this.random = new SecureRandom();
kParam = (AsymmetricKeyParameter)param;
}
engine.init(forEncryption, param);
this.forPrivateKey = kParam.isPrivate();
this.forEncryption = forEncryption;
}
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 /* Lenght 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 = null;
if (this.fallback == null)
{
random = new byte[this.pLen];
this.random.nextBytes(random);
}
else
{
random = fallback;
}
/*
* TODO: This is a potential dangerous side channel. However, you can
* fix this by changing the RSA engine in a way, that it will always
* return blocks of the same length and prepend them with 0 bytes if
* needed.
*/
if (block.length < getOutputBlockSize())
{
throw new InvalidCipherTextException("block truncated");
}
/*
* TODO: Potential side channel. Fix it by making the engine always
* return blocks of the correct length.
*/
if (useStrictLength && block.length != engine.getOutputBlockSize())
{
throw new InvalidCipherTextException("block incorrect size");
}
/*
* Check the padding.
*/
int correct = PKCS1Encoding.checkPkcs1Encoding(block, 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)((block[i + (block.length - pLen)] & (~correct)) | (random[i] & correct));
}
return result;
}
/**
* @exception 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);
if (block.length < getOutputBlockSize())
{
throw new InvalidCipherTextException("block truncated");
}
byte type = block[0];
if (forPrivateKey)
{
if (type != 2)
{
throw new InvalidCipherTextException("unknown block type");
}
}
else
{
if (type != 1)
{
throw new InvalidCipherTextException("unknown block type");
}
}
if (useStrictLength && block.length != engine.getOutputBlockSize())
{
throw new InvalidCipherTextException("block incorrect size");
}
//
// find and extract the message block.
//
int start;
for (start = 1; start != block.length; start++)
{
byte pad = block[start];
if (pad == 0)
{
break;
}
if (type == 1 && pad != (byte)0xff)
{
throw new InvalidCipherTextException("block padding incorrect");
}
}
start++; // data should start at the next byte
if (start > block.length || start < HEADER_LENGTH)
{
throw new InvalidCipherTextException("no data in block");
}
byte[] result = new byte[block.length - start];
System.arraycopy(block, start, result, 0, result.length);
return result;
}
}