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.
/**
 * 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.

The system property is checked during construction of the encoding object, it is set to 
true by default.

/**
     * 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;

    
Basic constructor.
Params:
cipher – /**
     * Basic constructor.
     * @param cipher
     */
    public PKCS1Encoding(
        AsymmetricBlockCipher   cipher)
    {
        this.engine = cipher;
        this.useStrictLength = useStrict();
    }   

    //
    // 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);
    }

    
Throws:
InvalidCipherTextException – if the decrypted block is not in PKCS1 format./**
     * @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;
    }
}