package org.bouncycastle.crypto.params;

import org.bouncycastle.crypto.DerivationParameters;
import org.bouncycastle.util.Arrays;

This KDF has been defined by the publicly available NIST SP 800-108 specification.
NIST SP800-108 allows for alternative orderings of the input fields, meaning that the input can be formated in multiple ways.
There are 3 supported formats:  - Below [i]_2 is a counter of r-bits length concatenated to the fixedInputData.

1: K(i) := PRF( KI, [i]_2 || Label || 0x00 || Context || [L]_2 ) with the counter at the very beginning of the fixedInputData (The default implementation has this format)
2: K(i) := PRF( KI, Label || 0x00 || Context || [L]_2 || [i]_2 ) with the counter at the very end of the fixedInputData
3a: K(i) := PRF( KI, Label || 0x00 || [i]_2 || Context || [L]_2 ) OR:
3b: K(i) := PRF( KI, Label || 0x00 || [i]_2 || [L]_2 || Context ) OR:
3c: K(i) := PRF( KI, Label || [i]_2 || 0x00 || Context || [L]_2 ) etc... with the counter somewhere in the 'middle' of the fixedInputData.

This function must be called with the following KDFCounterParameters():

 
KI
 
The part of the fixedInputData that comes BEFORE the counter OR null
 
the part of the fixedInputData that comes AFTER the counter OR null
 
the length of the counter in bits (not bytes)
 
Resulting function calls assuming an 8 bit counter.

1.  KDFCounterParameters(ki, 	null, 									"Label || 0x00 || Context || [L]_2]",	8); 
2.  KDFCounterParameters(ki, 	"Label || 0x00 || Context || [L]_2]", 	null,									8); 
3a. KDFCounterParameters(ki, 	"Label || 0x00",						"Context || [L]_2]",					8);  
3b. KDFCounterParameters(ki, 	"Label || 0x00",						"[L]_2] || Context",					8);
3c. KDFCounterParameters(ki, 	"Label", 								"0x00 || Context || [L]_2]",			8); 

/**
 * This KDF has been defined by the publicly available NIST SP 800-108 specification.
 * NIST SP800-108 allows for alternative orderings of the input fields, meaning that the input can be formated in multiple ways.
 * There are 3 supported formats:  - Below [i]_2 is a counter of r-bits length concatenated to the fixedInputData.
 * <ul>
 * <li>1: K(i) := PRF( KI, [i]_2 || Label || 0x00 || Context || [L]_2 ) with the counter at the very beginning of the fixedInputData (The default implementation has this format)</li>
 * <li>2: K(i) := PRF( KI, Label || 0x00 || Context || [L]_2 || [i]_2 ) with the counter at the very end of the fixedInputData</li>
 * <li>3a: K(i) := PRF( KI, Label || 0x00 || [i]_2 || Context || [L]_2 ) OR:</li>
 * <li>3b: K(i) := PRF( KI, Label || 0x00 || [i]_2 || [L]_2 || Context ) OR:</li>
 * <li>3c: K(i) := PRF( KI, Label || [i]_2 || 0x00 || Context || [L]_2 ) etc... with the counter somewhere in the 'middle' of the fixedInputData.</li>
 * </ul>
 * This function must be called with the following KDFCounterParameters():
 * <ul>
 *  <li>KI</li>
 *  <li>The part of the fixedInputData that comes BEFORE the counter OR null</li>
 *  <li>the part of the fixedInputData that comes AFTER the counter OR null</li>
 *  <li>the length of the counter in bits (not bytes)</li>
 *  </ul>
 * Resulting function calls assuming an 8 bit counter.
 * <ul>
 * <li>1.  KDFCounterParameters(ki, 	null, 									"Label || 0x00 || Context || [L]_2]",	8); </li>
 * <li>2.  KDFCounterParameters(ki, 	"Label || 0x00 || Context || [L]_2]", 	null,									8); </li>
 * <li>3a. KDFCounterParameters(ki, 	"Label || 0x00",						"Context || [L]_2]",					8);  </li>
 * <li>3b. KDFCounterParameters(ki, 	"Label || 0x00",						"[L]_2] || Context",					8);</li>
 * <li>3c. KDFCounterParameters(ki, 	"Label", 								"0x00 || Context || [L]_2]",			8); </li>
 * </ul>
 */
public final class KDFCounterParameters
    implements DerivationParameters
{

    private byte[] ki;
    private byte[] fixedInputDataCounterPrefix;
    private byte[] fixedInputDataCounterSuffix;
    private int r;

    
Base constructor - suffix fixed input data only.
Params:
ki – the KDF seed
fixedInputDataCounterSuffix –  fixed input data to follow counter.
r – length of the counter in bits./**
     * Base constructor - suffix fixed input data only.
     *
     * @param ki the KDF seed
     * @param fixedInputDataCounterSuffix  fixed input data to follow counter.
     * @param r length of the counter in bits.
     */
    public KDFCounterParameters(byte[] ki, byte[] fixedInputDataCounterSuffix, int r)
    {
    	this(ki, null, fixedInputDataCounterSuffix, r);
    }

    
Base constructor - prefix and suffix fixed input data.
Params:
ki – the KDF seed
fixedInputDataCounterPrefix – fixed input data to precede counter
fixedInputDataCounterSuffix – fixed input data to follow counter.
r – length of the counter in bits./**
     * Base constructor - prefix and suffix fixed input data.
     *
     * @param ki the KDF seed
     * @param fixedInputDataCounterPrefix fixed input data to precede counter
     * @param fixedInputDataCounterSuffix fixed input data to follow counter.
     * @param r length of the counter in bits.
     */
    public KDFCounterParameters(byte[] ki, byte[] fixedInputDataCounterPrefix, byte[] fixedInputDataCounterSuffix, int r)
    {
        if (ki == null)
        {
            throw new IllegalArgumentException("A KDF requires Ki (a seed) as input");
        }
        this.ki = Arrays.clone(ki);

        if (fixedInputDataCounterPrefix == null)
        {
            this.fixedInputDataCounterPrefix = new byte[0];
        }
        else
        {
            this.fixedInputDataCounterPrefix = Arrays.clone(fixedInputDataCounterPrefix);
        }
        
        if (fixedInputDataCounterSuffix == null)
        {
            this.fixedInputDataCounterSuffix = new byte[0];
        }
        else
        {
            this.fixedInputDataCounterSuffix = Arrays.clone(fixedInputDataCounterSuffix);
        }

        if (r != 8 && r != 16 && r != 24 && r != 32)
        {
            throw new IllegalArgumentException("Length of counter should be 8, 16, 24 or 32");
        }
        this.r = r;
    }
    
    public byte[] getKI()
    {
        return ki;
    }

    public byte[] getFixedInputData()
    {
    	//Retained for backwards compatibility
        return Arrays.clone(fixedInputDataCounterSuffix);
    }

    public byte[] getFixedInputDataCounterPrefix()
    {
        return Arrays.clone(fixedInputDataCounterPrefix);
    }
    
    public byte[] getFixedInputDataCounterSuffix()
    {
        return Arrays.clone(fixedInputDataCounterSuffix);
    }

    public int getR()
    {
        return r;
    }
}