RSAEngine.java

package org.bouncycastle.crypto.engines;

import org.bouncycastle.crypto.AsymmetricBlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;

/**
 * this does your basic RSA algorithm.
 */
public class RSAEngine implements AsymmetricBlockCipher {
    private RSACoreEngine core;

    /**
     * initialise the RSA engine.
     * 
     * @param forEncryption true if we are encrypting, false otherwise.
     * @param param the necessary RSA key parameters.
     */
    public void init(boolean forEncryption, CipherParameters param) {
        if (core == null) {
            core = new RSACoreEngine();
        }

        core.init(forEncryption, param);
    }

    /**
     * Return the maximum size for an input block to this engine. For RSA this
     * is always one byte less than the key size on encryption, and the same
     * length as the key size on decryption.
     * 
     * @return maximum size for an input block.
     */
    public int getInputBlockSize() {
        return core.getInputBlockSize();
    }

    /**
     * Return the maximum size for an output block to this engine. For RSA this
     * is always one byte less than the key size on decryption, and the same
     * length as the key size on encryption.
     * 
     * @return maximum size for an output block.
     */
    public int getOutputBlockSize() {
        return core.getOutputBlockSize();
    }

    /**
     * Process a single block using the basic RSA algorithm.
     * 
     * @param in the input array.
     * @param inOff the offset into the input buffer where the data starts.
     * @param inLen the length of the data to be processed.
     * @return the result of the RSA process.
     * @exception DataLengthException the input block is too large.
     */
    public byte[] processBlock(byte[] in, int inOff, int inLen) {
        if (core == null) {
            throw new IllegalStateException("RSA engine not initialised");
        }

        return core.convertOutput(core.processBlock(core.convertInput(in, inOff, inLen)));
    }
}