https://openjdk.java.net/ 
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
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package com.sun.crypto.provider;

import java.util.*;
import java.lang.*;
import java.math.BigInteger;
import java.security.AccessController;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.PrivilegedAction;
import java.security.ProviderException;
import java.security.spec.AlgorithmParameterSpec;
import java.security.spec.InvalidKeySpecException;
import javax.crypto.KeyAgreementSpi;
import javax.crypto.ShortBufferException;
import javax.crypto.SecretKey;
import javax.crypto.spec.*;

import sun.security.util.KeyUtil;


This class implements the Diffie-Hellman key agreement protocol between
any number of parties.

Author:Jan Luehe
/**
 * This class implements the Diffie-Hellman key agreement protocol between
 * any number of parties.
 *
 * @author Jan Luehe
 *
 */

public final class DHKeyAgreement
extends KeyAgreementSpi {

    private boolean generateSecret = false;
    private BigInteger init_p = null;
    private BigInteger init_g = null;
    private BigInteger x = BigInteger.ZERO; // the private value
    private BigInteger y = BigInteger.ZERO;

    private static class AllowKDF {

        private static final boolean VALUE = getValue();

        private static boolean getValue() {
            return AccessController.doPrivileged(
                (PrivilegedAction<Boolean>)
                () -> Boolean.getBoolean("jdk.crypto.KeyAgreement.legacyKDF"));
        }
    }

    
Empty constructor

/**
     * Empty constructor
     */
    public DHKeyAgreement() {
    }

    
Initializes this key agreement with the given key and source of
randomness. The given key is required to contain all the algorithm
parameters required for this key agreement.

 If the key agreement algorithm requires random bytes, it gets them
from the given source of randomness, random.
However, if the underlying
algorithm implementation does not require any random bytes,
random is ignored.

Params:
  • key – the party's private information. For example, in the case
of the Diffie-Hellman key agreement, this would be the party's own
Diffie-Hellman private key.
  • random – the source of randomness
Throws:
  • InvalidKeyException – if the given key is
inappropriate for this key agreement, e.g., is of the wrong type or
has an incompatible algorithm type.
/**
     * Initializes this key agreement with the given key and source of
     * randomness. The given key is required to contain all the algorithm
     * parameters required for this key agreement.
     *
     * <p> If the key agreement algorithm requires random bytes, it gets them
     * from the given source of randomness, <code>random</code>.
     * However, if the underlying
     * algorithm implementation does not require any random bytes,
     * <code>random</code> is ignored.
     *
     * @param key the party's private information. For example, in the case
     * of the Diffie-Hellman key agreement, this would be the party's own
     * Diffie-Hellman private key.
     * @param random the source of randomness
     *
     * @exception InvalidKeyException if the given key is
     * inappropriate for this key agreement, e.g., is of the wrong type or
     * has an incompatible algorithm type.
     */
    protected void engineInit(Key key, SecureRandom random)
        throws InvalidKeyException
    {
        try {
            engineInit(key, null, random);
        } catch (InvalidAlgorithmParameterException e) {
            // never happens, because we did not pass any parameters
        }
    }

    
Initializes this key agreement with the given key, set of
algorithm parameters, and source of randomness.

Params:
  • key – the party's private information. For example, in the case
of the Diffie-Hellman key agreement, this would be the party's own
Diffie-Hellman private key.
  • params – the key agreement parameters
  • random – the source of randomness
Throws:
/**
     * Initializes this key agreement with the given key, set of
     * algorithm parameters, and source of randomness.
     *
     * @param key the party's private information. For example, in the case
     * of the Diffie-Hellman key agreement, this would be the party's own
     * Diffie-Hellman private key.
     * @param params the key agreement parameters
     * @param random the source of randomness
     *
     * @exception InvalidKeyException if the given key is
     * inappropriate for this key agreement, e.g., is of the wrong type or
     * has an incompatible algorithm type.
     * @exception InvalidAlgorithmParameterException if the given parameters
     * are inappropriate for this key agreement.
     */
    protected void engineInit(Key key, AlgorithmParameterSpec params,
                              SecureRandom random)
        throws InvalidKeyException, InvalidAlgorithmParameterException
    {
        // ignore "random" parameter, because our implementation does not
        // require any source of randomness
        generateSecret = false;
        init_p = null;
        init_g = null;

        if ((params != null) && !(params instanceof DHParameterSpec)) {
            throw new InvalidAlgorithmParameterException
                ("Diffie-Hellman parameters expected");
        }
        if (!(key instanceof javax.crypto.interfaces.DHPrivateKey)) {
            throw new InvalidKeyException("Diffie-Hellman private key "
                                          + "expected");
        }
        javax.crypto.interfaces.DHPrivateKey dhPrivKey;
        dhPrivKey = (javax.crypto.interfaces.DHPrivateKey)key;

        // check if private key parameters are compatible with
        // initialized ones
        if (params != null) {
            init_p = ((DHParameterSpec)params).getP();
            init_g = ((DHParameterSpec)params).getG();
        }
        BigInteger priv_p = dhPrivKey.getParams().getP();
        BigInteger priv_g = dhPrivKey.getParams().getG();
        if (init_p != null && priv_p != null && !(init_p.equals(priv_p))) {
            throw new InvalidKeyException("Incompatible parameters");
        }
        if (init_g != null && priv_g != null && !(init_g.equals(priv_g))) {
            throw new InvalidKeyException("Incompatible parameters");
        }
        if ((init_p == null && priv_p == null)
            || (init_g == null && priv_g == null)) {
            throw new InvalidKeyException("Missing parameters");
        }
        init_p = priv_p;
        init_g = priv_g;

        // store the x value
        this.x = dhPrivKey.getX();
    }

    
Executes the next phase of this key agreement with the given
key that was received from one of the other parties involved in this key
agreement.

Params:
  • key – the key for this phase. For example, in the case of
Diffie-Hellman between 2 parties, this would be the other party's
Diffie-Hellman public key.
  • lastPhase – flag which indicates whether or not this is the last
phase of this key agreement.
Throws:
Returns:the (intermediate) key resulting from this phase, or null if
this phase does not yield a key
/**
     * Executes the next phase of this key agreement with the given
     * key that was received from one of the other parties involved in this key
     * agreement.
     *
     * @param key the key for this phase. For example, in the case of
     * Diffie-Hellman between 2 parties, this would be the other party's
     * Diffie-Hellman public key.
     * @param lastPhase flag which indicates whether or not this is the last
     * phase of this key agreement.
     *
     * @return the (intermediate) key resulting from this phase, or null if
     * this phase does not yield a key
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * this phase.
     * @exception IllegalStateException if this key agreement has not been
     * initialized.
     */
    protected Key engineDoPhase(Key key, boolean lastPhase)
        throws InvalidKeyException, IllegalStateException
    {
        if (!(key instanceof javax.crypto.interfaces.DHPublicKey)) {
            throw new InvalidKeyException("Diffie-Hellman public key "
                                          + "expected");
        }
        javax.crypto.interfaces.DHPublicKey dhPubKey;
        dhPubKey = (javax.crypto.interfaces.DHPublicKey)key;

        if (init_p == null || init_g == null) {
            throw new IllegalStateException("Not initialized");
        }

        // check if public key parameters are compatible with
        // initialized ones
        BigInteger pub_p = dhPubKey.getParams().getP();
        BigInteger pub_g = dhPubKey.getParams().getG();
        if (pub_p != null && !(init_p.equals(pub_p))) {
            throw new InvalidKeyException("Incompatible parameters");
        }
        if (pub_g != null && !(init_g.equals(pub_g))) {
            throw new InvalidKeyException("Incompatible parameters");
        }

        // validate the Diffie-Hellman public key
        KeyUtil.validate(dhPubKey);

        // store the y value
        this.y = dhPubKey.getY();

        // we've received a public key (from one of the other parties),
        // so we are ready to create the secret, which may be an
        // intermediate secret, in which case we wrap it into a
        // Diffie-Hellman public key object and return it.
        generateSecret = true;
        if (lastPhase == false) {
            byte[] intermediate = engineGenerateSecret();
            return new DHPublicKey(new BigInteger(1, intermediate),
                                   init_p, init_g);
        } else {
            return null;
        }
    }

    
Generates the shared secret and returns it in a new buffer.

This method resets this KeyAgreementSpi object,
so that it
can be reused for further key agreements. Unless this key agreement is
reinitialized with one of the engineInit methods, the same
private information and algorithm parameters will be used for
subsequent key agreements.

Throws:
Returns:the new buffer with the shared secret
/**
     * Generates the shared secret and returns it in a new buffer.
     *
     * <p>This method resets this <code>KeyAgreementSpi</code> object,
     * so that it
     * can be reused for further key agreements. Unless this key agreement is
     * reinitialized with one of the <code>engineInit</code> methods, the same
     * private information and algorithm parameters will be used for
     * subsequent key agreements.
     *
     * @return the new buffer with the shared secret
     *
     * @exception IllegalStateException if this key agreement has not been
     * completed yet
     */
    protected byte[] engineGenerateSecret()
        throws IllegalStateException
    {
        int expectedLen = (init_p.bitLength() + 7) >>> 3;
        byte[] result = new byte[expectedLen];
        try {
            engineGenerateSecret(result, 0);
        } catch (ShortBufferException sbe) {
            // should never happen since length are identical
        }
        return result;
    }

    
Generates the shared secret, and places it into the buffer
sharedSecret, beginning at offset.

If the sharedSecret buffer is too small to hold the
result, a ShortBufferException is thrown.
In this case, this call should be repeated with a larger output buffer.

This method resets this KeyAgreementSpi object,
so that it
can be reused for further key agreements. Unless this key agreement is
reinitialized with one of the engineInit methods, the same
private information and algorithm parameters will be used for
subsequent key agreements.

Params:
  • sharedSecret – the buffer for the shared secret
  • offset – the offset in sharedSecret where the
shared secret will be stored
Throws:
Returns:the number of bytes placed into sharedSecret
/**
     * Generates the shared secret, and places it into the buffer
     * <code>sharedSecret</code>, beginning at <code>offset</code>.
     *
     * <p>If the <code>sharedSecret</code> buffer is too small to hold the
     * result, a <code>ShortBufferException</code> is thrown.
     * In this case, this call should be repeated with a larger output buffer.
     *
     * <p>This method resets this <code>KeyAgreementSpi</code> object,
     * so that it
     * can be reused for further key agreements. Unless this key agreement is
     * reinitialized with one of the <code>engineInit</code> methods, the same
     * private information and algorithm parameters will be used for
     * subsequent key agreements.
     *
     * @param sharedSecret the buffer for the shared secret
     * @param offset the offset in <code>sharedSecret</code> where the
     * shared secret will be stored
     *
     * @return the number of bytes placed into <code>sharedSecret</code>
     *
     * @exception IllegalStateException if this key agreement has not been
     * completed yet
     * @exception ShortBufferException if the given output buffer is too small
     * to hold the secret
     */
    protected int engineGenerateSecret(byte[] sharedSecret, int offset)
        throws IllegalStateException, ShortBufferException
    {
        if (generateSecret == false) {
            throw new IllegalStateException
                ("Key agreement has not been completed yet");
        }

        if (sharedSecret == null) {
            throw new ShortBufferException
                ("No buffer provided for shared secret");
        }

        BigInteger modulus = init_p;
        int expectedLen = (modulus.bitLength() + 7) >>> 3;
        if ((sharedSecret.length - offset) < expectedLen) {
            throw new ShortBufferException
                    ("Buffer too short for shared secret");
        }

        // Reset the key agreement after checking for ShortBufferException
        // above, so user can recover w/o losing internal state
        generateSecret = false;

        /*
         * NOTE: BigInteger.toByteArray() returns a byte array containing
         * the two's-complement representation of this BigInteger with
         * the most significant byte is in the zeroth element. This
         * contains the minimum number of bytes required to represent
         * this BigInteger, including at least one sign bit whose value
         * is always 0.
         *
         * Keys are always positive, and the above sign bit isn't
         * actually used when representing keys.  (i.e. key = new
         * BigInteger(1, byteArray))  To obtain an array containing
         * exactly expectedLen bytes of magnitude, we strip any extra
         * leading 0's, or pad with 0's in case of a "short" secret.
         */
        byte[] secret = this.y.modPow(this.x, modulus).toByteArray();
        if (secret.length == expectedLen) {
            System.arraycopy(secret, 0, sharedSecret, offset,
                             secret.length);
        } else {
            // Array too short, pad it w/ leading 0s
            if (secret.length < expectedLen) {
                System.arraycopy(secret, 0, sharedSecret,
                    offset + (expectedLen - secret.length),
                    secret.length);
            } else {
                // Array too long, check and trim off the excess
                if ((secret.length == (expectedLen+1)) && secret[0] == 0) {
                    // ignore the leading sign byte
                    System.arraycopy(secret, 1, sharedSecret, offset, expectedLen);
                } else {
                    throw new ProviderException("Generated secret is out-of-range");
                }
            }
        }
        return expectedLen;
    }

    
Creates the shared secret and returns it as a secret key object
of the requested algorithm type.

This method resets this KeyAgreementSpi object,
so that it
can be reused for further key agreements. Unless this key agreement is
reinitialized with one of the engineInit methods, the same
private information and algorithm parameters will be used for
subsequent key agreements.

Params:
  • algorithm – the requested secret key algorithm
Throws:
  • IllegalStateException – if this key agreement has not been
completed yet
  • NoSuchAlgorithmException – if the requested secret key
algorithm is not available
  • InvalidKeyException – if the shared secret key material cannot
be used to generate a secret key of the requested algorithm type (e.g.,
the key material is too short)
Returns:the shared secret key
/**
     * Creates the shared secret and returns it as a secret key object
     * of the requested algorithm type.
     *
     * <p>This method resets this <code>KeyAgreementSpi</code> object,
     * so that it
     * can be reused for further key agreements. Unless this key agreement is
     * reinitialized with one of the <code>engineInit</code> methods, the same
     * private information and algorithm parameters will be used for
     * subsequent key agreements.
     *
     * @param algorithm the requested secret key algorithm
     *
     * @return the shared secret key
     *
     * @exception IllegalStateException if this key agreement has not been
     * completed yet
     * @exception NoSuchAlgorithmException if the requested secret key
     * algorithm is not available
     * @exception InvalidKeyException if the shared secret key material cannot
     * be used to generate a secret key of the requested algorithm type (e.g.,
     * the key material is too short)
     */
    protected SecretKey engineGenerateSecret(String algorithm)
        throws IllegalStateException, NoSuchAlgorithmException,
            InvalidKeyException
    {
        if (algorithm == null) {
            throw new NoSuchAlgorithmException("null algorithm");
        }

        if (!algorithm.equalsIgnoreCase("TlsPremasterSecret") &&
            !AllowKDF.VALUE) {

            throw new NoSuchAlgorithmException("Unsupported secret key "
                                               + "algorithm: " + algorithm);
        }

        byte[] secret = engineGenerateSecret();
        if (algorithm.equalsIgnoreCase("DES")) {
            // DES
            return new DESKey(secret);
        } else if (algorithm.equalsIgnoreCase("DESede")
                   || algorithm.equalsIgnoreCase("TripleDES")) {
            // Triple DES
            return new DESedeKey(secret);
        } else if (algorithm.equalsIgnoreCase("Blowfish")) {
            // Blowfish
            int keysize = secret.length;
            if (keysize >= BlowfishConstants.BLOWFISH_MAX_KEYSIZE)
                keysize = BlowfishConstants.BLOWFISH_MAX_KEYSIZE;
            SecretKeySpec skey = new SecretKeySpec(secret, 0, keysize,
                                                   "Blowfish");
            return skey;
        } else if (algorithm.equalsIgnoreCase("AES")) {
            // AES
            int keysize = secret.length;
            SecretKeySpec skey = null;
            int idx = AESConstants.AES_KEYSIZES.length - 1;
            while (skey == null && idx >= 0) {
                // Generate the strongest key using the shared secret
                // assuming the key sizes in AESConstants class are
                // in ascending order
                if (keysize >= AESConstants.AES_KEYSIZES[idx]) {
                    keysize = AESConstants.AES_KEYSIZES[idx];
                    skey = new SecretKeySpec(secret, 0, keysize, "AES");
                }
                idx--;
            }
            if (skey == null) {
                throw new InvalidKeyException("Key material is too short");
            }
            return skey;
        } else if (algorithm.equals("TlsPremasterSecret")) {
            // remove leading zero bytes per RFC 5246 Section 8.1.2
            return new SecretKeySpec(
                        KeyUtil.trimZeroes(secret), "TlsPremasterSecret");
        } else {
            throw new NoSuchAlgorithmException("Unsupported secret key "
                                               + "algorithm: "+ algorithm);
        }
    }
}