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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.8 and up. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.
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package org.bouncycastle.cert.crmf;

import java.io.ByteArrayOutputStream;
import java.io.OutputStream;
import java.security.SecureRandom;

import org.bouncycastle.asn1.DERNull;
import org.bouncycastle.asn1.cmp.CMPObjectIdentifiers;
import org.bouncycastle.asn1.cmp.PBMParameter;
import org.bouncycastle.asn1.iana.IANAObjectIdentifiers;
import org.bouncycastle.asn1.oiw.OIWObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.operator.GenericKey;
import org.bouncycastle.operator.MacCalculator;
import org.bouncycastle.operator.OperatorCreationException;
import org.bouncycastle.operator.PBEMacCalculatorProvider;
import org.bouncycastle.operator.RuntimeOperatorException;
import org.bouncycastle.util.Strings;

public class PKMACBuilder
    implements PBEMacCalculatorProvider
{
    private AlgorithmIdentifier owf;
    private int iterationCount;
    private AlgorithmIdentifier mac;
    private int saltLength = 20;
    private SecureRandom random;
    private PKMACValuesCalculator calculator;
    private PBMParameter parameters;
    private int maxIterations;

    public PKMACBuilder(PKMACValuesCalculator calculator)
    {
        this(new AlgorithmIdentifier(OIWObjectIdentifiers.idSHA1), 1000,
            new AlgorithmIdentifier(IANAObjectIdentifiers.hmacSHA1, DERNull.INSTANCE), calculator);
    }

    /**
     * Create a PKMAC builder enforcing a ceiling on the maximum iteration count.
     *
     * @param calculator     supporting calculator
     * @param maxIterations  max allowable value for iteration count.
     */
    public PKMACBuilder(PKMACValuesCalculator calculator, int maxIterations)
    {
        this.maxIterations = maxIterations;
        this.calculator = calculator;
    }

    private PKMACBuilder(AlgorithmIdentifier hashAlgorithm, int iterationCount, AlgorithmIdentifier macAlgorithm,
        PKMACValuesCalculator calculator)
    {
        this.owf = hashAlgorithm;
        this.iterationCount = iterationCount;
        this.mac = macAlgorithm;
        this.calculator = calculator;
    }

    /**
     * Set the salt length in octets.
     *
     * @param saltLength length in octets of the salt to be generated.
     * @return the generator
     */
    public PKMACBuilder setSaltLength(int saltLength)
    {
        if (saltLength < 8)
        {
            throw new IllegalArgumentException("salt length must be at least 8 bytes");
        }

        this.saltLength = saltLength;

        return this;
    }

    public PKMACBuilder setIterationCount(int iterationCount)
    {
        if (iterationCount < 100)
        {
            throw new IllegalArgumentException("iteration count must be at least 100");
        }
        checkIterationCountCeiling(iterationCount);

        this.iterationCount = iterationCount;

        return this;
    }

    public PKMACBuilder setSecureRandom(SecureRandom random)
    {
        this.random = random;

        return this;
    }

    public PKMACBuilder setParameters(PBMParameter parameters)
    {
        checkIterationCountCeiling(parameters.getIterationCount().intValueExact());

        this.parameters = parameters;

        return this;
    }

    public MacCalculator get(AlgorithmIdentifier algorithm, char[] password)
        throws OperatorCreationException
    {
        if (!CMPObjectIdentifiers.passwordBasedMac.equals(algorithm.getAlgorithm()))
        {
            throw new OperatorCreationException("protection algorithm not mac based");
        }

        this.setParameters(PBMParameter.getInstance(algorithm.getParameters()));

        try
        {
            return this.build(password);
        }
        catch (CRMFException e)
        {
            throw new OperatorCreationException(e.getMessage(), e.getCause());
        }
    }

    public MacCalculator build(char[] password)
        throws CRMFException
    {
        PBMParameter pbmParameter = parameters;        
        if (pbmParameter == null)
        {
            pbmParameter = genParameters();
        }

        return genCalculator(pbmParameter, password);
    }

    private void checkIterationCountCeiling(int iterationCount)
    {
        if (maxIterations > 0 && iterationCount > maxIterations)
        {
            throw new IllegalArgumentException("iteration count exceeds limit (" + iterationCount + " > " + maxIterations + ")");
        }
    }

    private MacCalculator genCalculator(final PBMParameter params, char[] password)
        throws CRMFException
    {
        // From RFC 4211
        //
        //   1.  Generate a random salt value S
        //
        //   2.  Append the salt to the pw.  K = pw || salt.
        //
        //   3.  Hash the value of K.  K = HASH(K)
        //
        //   4.  Iter = Iter - 1.  If Iter is greater than zero.  Goto step 3.
        //
        //   5.  Compute an HMAC as documented in [HMAC].
        //
        //       MAC = HASH( K XOR opad, HASH( K XOR ipad, data) )
        //
        //       Where opad and ipad are defined in [HMAC].
        byte[] pw = Strings.toUTF8ByteArray(password);
        byte[] salt = params.getSalt().getOctets();
        byte[] K = new byte[pw.length + salt.length];

        System.arraycopy(pw, 0, K, 0, pw.length);
        System.arraycopy(salt, 0, K, pw.length, salt.length);

        calculator.setup(params.getOwf(), params.getMac());

        int iter = params.getIterationCount().intValueExact();
        do
        {
            K = calculator.calculateDigest(K);
        }
        while (--iter > 0);

        final byte[] key = K;

        return new MacCalculator()
        {
            ByteArrayOutputStream bOut = new ByteArrayOutputStream();

            public AlgorithmIdentifier getAlgorithmIdentifier()
            {
                return new AlgorithmIdentifier(CMPObjectIdentifiers.passwordBasedMac, params);
            }

            public GenericKey getKey()
            {
                return new GenericKey(getAlgorithmIdentifier(), key);
            }

            public OutputStream getOutputStream()
            {
                return bOut;
            }

            public byte[] getMac()
            {
                try
                {
                    return calculator.calculateMac(key, bOut.toByteArray());
                }
                catch (CRMFException e)
                {
                    throw new RuntimeOperatorException("exception calculating mac: " + e.getMessage(), e);
                }
            }
        };
    }

    private PBMParameter genParameters()
    {
        byte[] salt = new byte[saltLength];

        if (random == null)
        {
            random = new SecureRandom();
        }

        random.nextBytes(salt);

        return new PBMParameter(salt, owf, iterationCount, mac);
    }
}