99 lines
4.4 KiB
C
99 lines
4.4 KiB
C
/* ctr_mode.h - TinyCrypt interface to CTR mode */
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/*
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* Copyright (C) 2015 by Intel Corporation, All Rights Reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* - Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* - Neither the name of Intel Corporation nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/**
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* @file
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* @brief Interface to CTR mode.
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*
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* Overview: CTR (pronounced "counter") mode is a NIST approved mode of
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* operation defined in SP 800-38a. It can be used with any
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* block cipher to provide confidentiality of strings of any
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* length. TinyCrypt hard codes AES128 as the block cipher.
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*
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* Security: CTR mode achieves confidentiality only if the counter value is
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* never reused with a same encryption key. If the counter is
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* repeated, than an adversary might be able to defeat the scheme.
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*
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* A usual method to ensure different counter values refers to
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* initialize the counter in a given value (0, for example) and
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* increases it every time a new block is enciphered. This naturally
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* leaves to a limitation on the number q of blocks that can be
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* enciphered using a same key: q < 2^(counter size).
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*
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* TinyCrypt uses a counter of 32 bits. This means that after 2^32
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* block encryptions, the counter will be reused (thus losing CBC
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* security). 2^32 block encryptions should be enough for most of
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* applications targeting constrained devices. Applications intended
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* to encrypt a larger number of blocks must replace the key after
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* 2^32 block encryptions.
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*
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* CTR mode provides NO data integrity.
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*
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* Requires: AES-128
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*
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* Usage: 1) call tc_ctr_mode to process the data to encrypt/decrypt.
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*
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*/
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#ifndef __TC_CTR_MODE_H__
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#define __TC_CTR_MODE_H__
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#include <aes.h>
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/**
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* @brief CTR mode encryption/decryption procedure.
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* CTR mode encrypts (or decrypts) inlen bytes from in buffer into out buffer
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* @return returns TC_SUCCESS (1)
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* returns TC_FAIL (0) if:
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* out == NULL or
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* in == NULL or
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* ctr == NULL or
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* sched == NULL or
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* inlen == 0 or
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* outlen == 0 or
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* inlen != outlen
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* @note Assumes:- The current value in ctr has NOT been used with sched
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* - out points to inlen bytes
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* - in points to inlen bytes
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* - ctr is an integer counter in littleEndian format
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* - sched was initialized by aes_set_encrypt_key
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* @param out OUT -- produced ciphertext (plaintext)
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* @param outlen IN -- length of ciphertext buffer in bytes
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* @param in IN -- data to encrypt (or decrypt)
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* @param inlen IN -- length of input data in bytes
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* @param ctr IN/OUT -- the current counter value
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* @param sched IN -- an initialized AES key schedule
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*/
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int32_t tc_ctr_mode(uint8_t *out, uint32_t outlen, const uint8_t *in,
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uint32_t inlen, uint8_t *ctr, const TCAesKeySched_t sched);
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#endif
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