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/*
* Copyright (C) 2013 Andreas Steffen
* HSR Hochschule fuer Technik Rapperswil
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public 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 Public License
* for more details.
*/
#include "ntru_mgf1.h"
#include <crypto/hashers/hasher.h>
#include <utils/debug.h>
#include <utils/test.h>
typedef struct private_ntru_mgf1_t private_ntru_mgf1_t;
/**
* Private data of an ntru_mgf1_t object.
*/
struct private_ntru_mgf1_t {
/**
* Public ntru_mgf1_t interface.
*/
ntru_mgf1_t public;
/**
* Hasher the MGF1 Mask Generation Function is based on
*/
hasher_t *hasher;
/**
* Counter
*/
u_int32_t counter;
/**
* Set if counter has reached 2^32
*/
bool overflow;
/**
* Current state to be hashed
*/
chunk_t state;
/**
* Position of the 4 octet counter string
*/
u_char *ctr_str;
};
METHOD(ntru_mgf1_t, get_hash_size, size_t,
private_ntru_mgf1_t *this)
{
return this->hasher->get_hash_size(this->hasher);
}
METHOD(ntru_mgf1_t, get_mask, bool,
private_ntru_mgf1_t *this, size_t mask_len, u_char *mask)
{
u_char buf[HASH_SIZE_SHA512];
size_t hash_len;
hash_len = this->hasher->get_hash_size(this->hasher);
while (mask_len > 0)
{
/* detect overflow, set counter string and increment counter */
if (this->overflow)
{
return FALSE;
}
htoun32(this->ctr_str, this->counter++);
if (this->counter == 0)
{
this->overflow = TRUE;
}
/* get the next or final mask block from the hash function */
if (!this->hasher->get_hash(this->hasher, this->state,
(mask_len < hash_len) ? buf : mask))
{
return FALSE;
}
if (mask_len < hash_len)
{
memcpy(mask, buf, mask_len);
return TRUE;
}
mask_len -= hash_len;
mask += hash_len;
}
return TRUE;
}
METHOD(ntru_mgf1_t, allocate_mask, bool,
private_ntru_mgf1_t *this, size_t mask_len, chunk_t *mask)
{
if (mask_len == 0)
{
*mask = chunk_empty;
return TRUE;
}
*mask = chunk_alloc(mask_len);
return get_mask(this, mask_len, mask->ptr);
}
METHOD(ntru_mgf1_t, destroy, void,
private_ntru_mgf1_t *this)
{
this->hasher->destroy(this->hasher);
chunk_clear(&this->state);
free(this);
}
/*
* Described in header.
*/
ntru_mgf1_t *ntru_mgf1_create(hash_algorithm_t alg, chunk_t seed,
bool hash_seed)
{
private_ntru_mgf1_t *this;
hasher_t *hasher;
size_t state_len;
if (seed.len == 0)
{
DBG1(DBG_LIB, "empty seed for MGF1");
return NULL;
}
hasher = lib->crypto->create_hasher(lib->crypto, alg);
if (!hasher)
{
DBG1(DBG_LIB, "failed to create %N hasher for MGF1",
hash_algorithm_names, alg);
return NULL;
}
state_len = (hash_seed ? hasher->get_hash_size(hasher) : seed.len) + 4;
INIT(this,
.public = {
.get_hash_size = _get_hash_size,
.allocate_mask = _allocate_mask,
.get_mask = _get_mask,
.destroy = _destroy,
},
.hasher = hasher,
.state = chunk_alloc(state_len),
);
/* determine position of the 4 octet counter string */
this->ctr_str = this->state.ptr + state_len - 4;
if (hash_seed)
{
if (!hasher->get_hash(hasher, seed, this->state.ptr))
{
DBG1(DBG_LIB, "failed to hash seed for MGF1");
destroy(this);
return NULL;
}
}
else
{
memcpy(this->state.ptr, seed.ptr, seed.len);
}
return &this->public;
}
EXPORT_FUNCTION_FOR_TESTS(ntru, ntru_mgf1_create);
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