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package org.spongycastle.crypto.encodings;
import org.spongycastle.crypto.AsymmetricBlockCipher;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.InvalidCipherTextException;
import org.spongycastle.crypto.params.AsymmetricKeyParameter;
import org.spongycastle.crypto.params.ParametersWithRandom;
import java.security.SecureRandom;
/**
* 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.spongycastle.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.spongycastle.pkcs1.strict";
private static final int HEADER_LENGTH = 10;
private SecureRandom random;
private AsymmetricBlockCipher engine;
private boolean forEncryption;
private boolean forPrivateKey;
private boolean useStrictLength;
/**
* Basic constructor.
* @param cipher
*/
public PKCS1Encoding(
AsymmetricBlockCipher cipher)
{
this.engine = cipher;
this.useStrictLength = useStrict();
}
//
// for J2ME compatibility
//
private boolean useStrict()
{
String strict = 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);
}
/**
* @exception InvalidCipherTextException if the decrypted block is not in PKCS1 format.
*/
private byte[] decodeBlock(
byte[] in,
int inOff,
int inLen)
throws InvalidCipherTextException
{
byte[] block = engine.processBlock(in, inOff, inLen);
if (block.length < getOutputBlockSize())
{
throw new InvalidCipherTextException("block truncated");
}
byte type = block[0];
if (type != 1 && type != 2)
{
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;
}
}
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