/**
 * @file hmac.c
 * 
 * @brief Implementation of hmac_t.
 */

/*
 * Copyright (C) 2005-2006 Martin Willi
 * Copyright (C) 2005 Jan Hutter
 * Hochschule fuer Technik Rapperswil
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General hmac License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General hmac License
 * for more details.
 */

#include <string.h>

#include "hmac.h"


typedef struct private_hmac_t private_hmac_t;

/**
 * Private data of a hmac_t object.
 * 
 * The variable names are the same as in the RFC.
 */
struct private_hmac_t {
	/**
	 * Public hmac_t interface.
	 */
	hmac_t hmac;
	
	/**
	 * Block size, as in RFC.
	 */
	u_int8_t b;
	
	/**
	 * Hash function.
	 */
	hasher_t *h;
	
	/**
	 * Previously xor'ed key using opad.
	 */
	chunk_t opaded_key;
	
	/**
	 * Previously xor'ed key using ipad.
	 */
	chunk_t ipaded_key;
};

/**
 * Implementation of hmac_t.get_mac.
 */
static void get_mac(private_hmac_t *this, chunk_t data, u_int8_t *out)
{
	/* H(K XOR opad, H(K XOR ipad, text)) 
	 * 
	 * if out is NULL, we append text to the inner hash.
	 * else, we complete the inner and do the outer.
	 * 
	 */
	
	u_int8_t buffer[this->h->get_hash_size(this->h)];
	chunk_t inner;
	
	if (out == NULL)
	{
		/* append data to inner */
		this->h->get_hash(this->h, data, NULL);
	}
	else
	{
		/* append and do outer hash */
		inner.ptr = buffer;
		inner.len = this->h->get_hash_size(this->h);
		
		/* complete inner */
		this->h->get_hash(this->h, data, buffer);
		
		/* do outer */
		this->h->get_hash(this->h, this->opaded_key, NULL);
		this->h->get_hash(this->h, inner, out);
		
		/* reinit for next call */
		this->h->get_hash(this->h, this->ipaded_key, NULL);
	}
}

/**
 * Implementation of hmac_t.allocate_mac.
 */
static void allocate_mac(private_hmac_t *this, chunk_t data, chunk_t *out)
{
	/* allocate space and use get_mac */
	if (out == NULL)
	{
		/* append mode */
		this->hmac.get_mac(&(this->hmac), data, NULL);
	}
	else
	{
		out->len = this->h->get_hash_size(this->h);
		out->ptr = malloc(out->len);
		this->hmac.get_mac(&(this->hmac), data, out->ptr);
	}
}
	
/**
 * Implementation of hmac_t.get_block_size.
 */
static size_t get_block_size(private_hmac_t *this)
{
	return this->h->get_hash_size(this->h);
}

/**
 * Implementation of hmac_t.set_key.
 */
static void set_key(private_hmac_t *this, chunk_t key)
{
	int i;
	u_int8_t buffer[this->b];
	
	memset(buffer, 0, this->b);
	
	if (key.len > this->b)
	{	
		/* if key is too long, it will be hashed */
		this->h->get_hash(this->h, key, buffer);
	}
	else
	{	
		/* if not, just copy it in our pre-padded k */
		memcpy(buffer, key.ptr, key.len);	
	}
			
	/* apply ipad and opad to key */
	for (i = 0; i < this->b; i++)
	{
		this->ipaded_key.ptr[i] = buffer[i] ^ 0x36;
		this->opaded_key.ptr[i] = buffer[i] ^ 0x5C;
	}
	
	/* begin hashing of inner pad */
	this->h->reset(this->h);
	this->h->get_hash(this->h, this->ipaded_key, NULL);
}

/**
 * Implementation of hmac_t.destroy.
 */
static void destroy(private_hmac_t *this)
{
	this->h->destroy(this->h);
	free(this->opaded_key.ptr);
	free(this->ipaded_key.ptr);
	free(this);
}

/*
 * Described in header
 */
hmac_t *hmac_create(hash_algorithm_t hash_algorithm)
{
	private_hmac_t *this;
	
	this = malloc_thing(private_hmac_t);

	/* set hmac_t methods */
	this->hmac.get_mac = (void (*)(hmac_t *,chunk_t,u_int8_t*))get_mac;
	this->hmac.allocate_mac = (void (*)(hmac_t *,chunk_t,chunk_t*))allocate_mac;
	this->hmac.get_block_size = (size_t (*)(hmac_t *))get_block_size;
	this->hmac.set_key = (void (*)(hmac_t *,chunk_t))set_key;
	this->hmac.destroy = (void (*)(hmac_t *))destroy;
	
	/* set b, according to hasher */
	switch (hash_algorithm)
	{
		case HASH_SHA1:
		case HASH_MD5:
		case HASH_SHA256:
			this->b = 64;
			break;
		case HASH_SHA384:
		case HASH_SHA512:
			this->b = 128;
			break;
		default:
			free(this);
			return NULL;	
	}
		
	/* build the hasher */
	this->h = hasher_create(hash_algorithm);

	/* build ipad and opad */
	this->opaded_key.ptr = malloc(this->b);
	this->opaded_key.len = this->b;

	this->ipaded_key.ptr = malloc(this->b);
	this->ipaded_key.len = this->b;

	return &(this->hmac);
}