| /* ctr_mode.h - TinyCrypt interface to CTR mode */ |
| |
| /* |
| * Copyright (C) 2017 by Intel Corporation, All Rights Reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are met: |
| * |
| * - Redistributions of source code must retain the above copyright notice, |
| * this list of conditions and the following disclaimer. |
| * |
| * - Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * - Neither the name of Intel Corporation nor the names of its contributors |
| * may be used to endorse or promote products derived from this software |
| * without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
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| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
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| */ |
| |
| /** |
| * @file |
| * @brief Interface to CTR mode. |
| * |
| * Overview: CTR (pronounced "counter") mode is a NIST approved mode of |
| * operation defined in SP 800-38a. It can be used with any |
| * block cipher to provide confidentiality of strings of any |
| * length. TinyCrypt hard codes AES128 as the block cipher. |
| * |
| * Security: CTR mode achieves confidentiality only if the counter value is |
| * never reused with a same encryption key. If the counter is |
| * repeated, than an adversary might be able to defeat the scheme. |
| * |
| * A usual method to ensure different counter values refers to |
| * initialize the counter in a given value (0, for example) and |
| * increases it every time a new block is enciphered. This naturally |
| * leaves to a limitation on the number q of blocks that can be |
| * enciphered using a same key: q < 2^(counter size). |
| * |
| * TinyCrypt uses a counter of 32 bits. This means that after 2^32 |
| * block encryptions, the counter will be reused (thus losing CBC |
| * security). 2^32 block encryptions should be enough for most of |
| * applications targeting constrained devices. Applications intended |
| * to encrypt a larger number of blocks must replace the key after |
| * 2^32 block encryptions. |
| * |
| * CTR mode provides NO data integrity. |
| * |
| * Requires: AES-128 |
| * |
| * Usage: 1) call tc_ctr_mode to process the data to encrypt/decrypt. |
| * |
| */ |
| |
| #ifndef __TC_CTR_MODE_H__ |
| #define __TC_CTR_MODE_H__ |
| |
| #include <tinycrypt/aes.h> |
| #include <tinycrypt/constants.h> |
| |
| #ifdef __cplusplus |
| extern "C" { |
| #endif |
| |
| /** |
| * @brief CTR mode encryption/decryption procedure. |
| * CTR mode encrypts (or decrypts) inlen bytes from in buffer into out buffer |
| * @return returns TC_CRYPTO_SUCCESS (1) |
| * returns TC_CRYPTO_FAIL (0) if: |
| * out == NULL or |
| * in == NULL or |
| * ctr == NULL or |
| * sched == NULL or |
| * inlen == 0 or |
| * outlen == 0 or |
| * inlen != outlen |
| * @note Assumes:- The current value in ctr has NOT been used with sched |
| * - out points to inlen bytes |
| * - in points to inlen bytes |
| * - ctr is an integer counter in littleEndian format |
| * - sched was initialized by aes_set_encrypt_key |
| * @param out OUT -- produced ciphertext (plaintext) |
| * @param outlen IN -- length of ciphertext buffer in bytes |
| * @param in IN -- data to encrypt (or decrypt) |
| * @param inlen IN -- length of input data in bytes |
| * @param ctr IN/OUT -- the current counter value |
| * @param sched IN -- an initialized AES key schedule |
| */ |
| int tc_ctr_mode(uint8_t *out, unsigned int outlen, const uint8_t *in, |
| unsigned int inlen, uint8_t *ctr, const TCAesKeySched_t sched); |
| |
| #ifdef __cplusplus |
| } |
| #endif |
| |
| #endif /* __TC_CTR_MODE_H__ */ |
