1 /* ctr_mode.h - TinyCrypt interface to CTR mode */ 2 3 /* 4 * Copyright (C) 2017 by Intel Corporation, All Rights Reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions are met: 8 * 9 * - Redistributions of source code must retain the above copyright notice, 10 * this list of conditions and the following disclaimer. 11 * 12 * - Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * - Neither the name of Intel Corporation nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 21 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 24 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 30 * POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33 /** 34 * @file 35 * @brief Interface to CTR mode. 36 * 37 * Overview: CTR (pronounced "counter") mode is a NIST approved mode of 38 * operation defined in SP 800-38a. It can be used with any 39 * block cipher to provide confidentiality of strings of any 40 * length. TinyCrypt hard codes AES128 as the block cipher. 41 * 42 * Security: CTR mode achieves confidentiality only if the counter value is 43 * never reused with a same encryption key. If the counter is 44 * repeated, than an adversary might be able to defeat the scheme. 45 * 46 * A usual method to ensure different counter values refers to 47 * initialize the counter in a given value (0, for example) and 48 * increases it every time a new block is enciphered. This naturally 49 * leaves to a limitation on the number q of blocks that can be 50 * enciphered using a same key: q < 2^(counter size). 51 * 52 * TinyCrypt uses a counter of 32 bits. This means that after 2^32 53 * block encryptions, the counter will be reused (thus losing CBC 54 * security). 2^32 block encryptions should be enough for most of 55 * applications targeting constrained devices. Applications intended 56 * to encrypt a larger number of blocks must replace the key after 57 * 2^32 block encryptions. 58 * 59 * CTR mode provides NO data integrity. 60 * 61 * Requires: AES-128 62 * 63 * Usage: 1) call tc_ctr_mode to process the data to encrypt/decrypt. 64 * 65 */ 66 67 #ifndef __TC_CTR_MODE_H__ 68 #define __TC_CTR_MODE_H__ 69 70 #include <tinycrypt/aes.h> 71 #include <tinycrypt/constants.h> 72 73 #ifdef __cplusplus 74 extern "C" { 75 #endif 76 77 /** 78 * @brief CTR mode encryption/decryption procedure. 79 * CTR mode encrypts (or decrypts) inlen bytes from in buffer into out buffer 80 * @return returns TC_CRYPTO_SUCCESS (1) 81 * returns TC_CRYPTO_FAIL (0) if: 82 * out == NULL or 83 * in == NULL or 84 * ctr == NULL or 85 * sched == NULL or 86 * inlen == 0 or 87 * outlen == 0 or 88 * inlen != outlen 89 * @note Assumes:- The current value in ctr has NOT been used with sched 90 * - out points to inlen bytes 91 * - in points to inlen bytes 92 * - ctr is an integer counter in littleEndian format 93 * - sched was initialized by aes_set_encrypt_key 94 * @param out OUT -- produced ciphertext (plaintext) 95 * @param outlen IN -- length of ciphertext buffer in bytes 96 * @param in IN -- data to encrypt (or decrypt) 97 * @param inlen IN -- length of input data in bytes 98 * @param ctr IN/OUT -- the current counter value 99 * @param blk_off IN/OUT -- the offset in the block 100 * @param sched IN -- an initialized AES key schedule 101 */ 102 int tc_ctr_mode(uint8_t *out, unsigned int outlen, const uint8_t *in, 103 unsigned int inlen, uint8_t *ctr, uint32_t *blk_off, 104 const TCAesKeySched_t sched); 105 106 #ifdef __cplusplus 107 } 108 #endif 109 110 #endif /* __TC_CTR_MODE_H__ */ 111
