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/*
 * IntegrityAlgorithm.java 
 * Created on 2011-07-21
 *
 * Copyright (c) Verax Systems 2011.
 * All rights reserved.
 *
 * This software is furnished under a license. Use, duplication,
 * disclosure and all other uses are restricted to the rights
 * specified in the written license agreement.
 */
package com.veraxsystems.vxipmi.coding.security;

import com.veraxsystems.vxipmi.coding.commands.session.Rakp1;
import com.veraxsystems.vxipmi.common.TypeConverter;

import java.security.InvalidKeyException;

/**
 * Interface for Integrity Algorithms. All classes extending this one must
 * implement constructor(byte[]).
 */
public abstract class IntegrityAlgorithm {

    protected byte[] sik;

    public IntegrityAlgorithm() {

    }

    /**
     * Initializes Integrity Algorithm
     *
     * @param sik
     *            - Session Integrity Key calculated during the opening of the
     *            session or user password if 'one-key' logins are enabled.
     */
    public void initialize(byte[] sik) throws InvalidKeyException {
        this.sik = sik;
    }

    /**
     * Returns the algorithm's ID.
     */
    public abstract byte getCode();

    /**
     * Creates AuthCode field for message.
     *
     * @param base
     *            - data starting with the AuthType/Format field up to and
     *            including the field that immediately precedes the AuthCode
     *            field
     * @return AuthCode field. Might be null if empty AuthCOde field is
     *         generated.
     *
     * @see Rakp1#calculateSik(com.veraxsystems.vxipmi.coding.commands.session.Rakp1ResponseData)
     */
    public abstract byte[] generateAuthCode(byte[] base);

    /**
     * Modifies the algorithm base since with null Auth Code during encoding
     * Integrity Pad isn't calculated.
     *
     * @param base
     *            - integrity algorithm base without Integrity Pad.
     * @param authCodeLength
     *            - expected length of the Auth Code field.
     * @return - integrity algorithm base with Integrity Pad and updated Pad
     *         Length field.
     */
    protected byte[] injectIntegrityPad(byte[] base, int authCodeLength) {
        int pad = 0;
        if ((base.length + authCodeLength) % 4 != 0) {
            pad = 4 - (base.length + authCodeLength) % 4;
        }

        if (pad != 0) {
            byte[] newBase = new byte[base.length + pad];

            System.arraycopy(base, 0, newBase, 0, base.length - 2);

            for (int i = base.length - 2; i < base.length - 2 + pad; ++i) {
                newBase[i] = TypeConverter.intToByte(0xff);
            }

            newBase[newBase.length - 2] = TypeConverter.intToByte(pad);

            newBase[newBase.length - 1] = base[base.length - 1];

            return newBase;
        } else {
            return base;
        }
    }
}