org.cryptacular.generator.SecretKeyGenerator.java Source code

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Here is the source code for org.cryptacular.generator.SecretKeyGenerator.java

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/* See LICENSE for licensing and NOTICE for copyright. */
package org.cryptacular.generator;

import java.security.SecureRandom;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.digests.SHA256Digest;
import org.bouncycastle.crypto.prng.SP800SecureRandomBuilder;
import org.cryptacular.util.NonceUtil;

/**
 * Factory class with static methods for generating {@link SecretKey}s.
 *
 * @author  Middleware Services
 */
public final class SecretKeyGenerator {

    /** Private constructor of static class. */
    private SecretKeyGenerator() {
    }

    /**
     * Generates a symmetric encryption key whose size is equal to the cipher
     * block size.
     *
     * @param  cipher  Cipher with with key will be used.
     *
     * @return  Symmetric encryption key.
     */
    public static SecretKey generate(final BlockCipher cipher) {
        return generate(cipher.getBlockSize() * 8, cipher);
    }

    /**
     * Generates a symmetric encryption key of the given length.
     *
     * @param  bitLength  Desired key length in bits.
     * @param  cipher  Cipher with with key will be used.
     *
     * @return  Symmetric encryption key.
     */
    public static SecretKey generate(final int bitLength, final BlockCipher cipher) {
        // Want as much nonce data as key bits
        final byte[] nonce = NonceUtil.timestampNonce((bitLength + 7) / 8);
        return generate(bitLength, cipher,
                new SP800SecureRandomBuilder().buildHash(new SHA256Digest(), nonce, false));
    }

    /**
     * Generates a symmetric encryption key of the given length.
     *
     * @param  bitLength  Desired key length in bits.
     * @param  cipher  Cipher with with key will be used.
     * @param  random  Randomness provider for key generation.
     *
     * @return  Symmetric encryption key.
     */
    public static SecretKey generate(final int bitLength, final BlockCipher cipher, final SecureRandom random) {
        // Round up for bit lengths that are not a multiple of 8
        final byte[] key = new byte[(bitLength + 7) / 8];
        random.nextBytes(key);
        return new SecretKeySpec(key, cipher.getAlgorithmName());
    }
}