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The FIPS 140-2 Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms certified to FIPS 140-2 level 1. This jar contains the debug version JCE provider and low-level API for the BC-FJA version 1.0.2.3, FIPS Certificate #3514. Please note the debug jar is not certified.

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package org.bouncycastle.crypto.fips;

import org.bouncycastle.crypto.internal.Mac;
import org.bouncycastle.crypto.internal.macs.CMac;
import org.bouncycastle.crypto.internal.macs.HMac;
import org.bouncycastle.crypto.internal.params.HKDFKeyParameters;
import org.bouncycastle.crypto.internal.params.KeyParameter;
import org.bouncycastle.crypto.internal.params.KeyParameterImpl;

/**
 * Two-Step KDF implemented according to NIST SP 800-56C.
 */
class TwoStepKeyGenerator
{
    private Mac mac;
    private int macLen;

    public TwoStepKeyGenerator(Mac mac)
    {
        this.mac = mac;
        if (mac instanceof HMac)
        {
            this.macLen = ((HMac)mac).getUnderlyingDigest().getDigestSize();
        }
        else
        {
            this.macLen = ((CMac)mac).getMacSize();
        }
    }

    public KeyParameter generate(HKDFKeyParameters params)
    {
        return extract(params.getSalt(), params.getIKM());
    }

    /**
     * Performs the extract part of the key derivation function.
     *
     * @param salt the salt to use
     * @param ikm  the input keying material
     * @return the PRK as KeyParameter
     */
    private KeyParameter extract(byte[] salt, byte[] ikm)
    {
        if (salt == null)
        {
            // TODO check if hashLen is indeed same as HMAC size
            mac.init(new KeyParameterImpl(new byte[macLen]));
        }
        else
        {
            mac.init(new KeyParameterImpl(salt));
        }

        mac.update(ikm, 0, ikm.length);

        byte[] prk = new byte[macLen];
        mac.doFinal(prk, 0);

        return new KeyParameterImpl(prk);
    }
}