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Annotation of src/usr.bin/ssh/cipher-aesctr.c, Revision 1.2

1.2     ! markus      1: /* $OpenBSD: cipher-aesctr.c,v 1.1 2014/04/29 15:39:33 markus Exp $ */
1.1       markus      2: /*
1.2     ! markus      3:  * Copyright (c) 2003 Markus Friedl.  All rights reserved.
1.1       markus      4:  *
                      5:  * Permission to use, copy, modify, and distribute this software for any
                      6:  * purpose with or without fee is hereby granted, provided that the above
                      7:  * copyright notice and this permission notice appear in all copies.
                      8:  *
                      9:  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
                     10:  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
                     11:  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
                     12:  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
                     13:  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
                     14:  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
                     15:  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
                     16:  */
                     17:
                     18: #include <sys/types.h>
                     19: #include <string.h>
                     20:
                     21: #include "cipher-aesctr.h"
                     22:
                     23: /*
                     24:  * increment counter 'ctr',
                     25:  * the counter is of size 'len' bytes and stored in network-byte-order.
                     26:  * (LSB at ctr[len-1], MSB at ctr[0])
                     27:  */
                     28: static __inline__ void
                     29: aesctr_inc(u8 *ctr, u32 len)
                     30: {
                     31:        ssize_t i;
                     32:
                     33: #ifndef CONSTANT_TIME_INCREMENT
                     34:        for (i = len - 1; i >= 0; i--)
                     35:                if (++ctr[i])   /* continue on overflow */
                     36:                        return;
                     37: #else
                     38:        u8 x, add = 1;
                     39:
                     40:        for (i = len - 1; i >= 0; i--) {
                     41:                ctr[i] += add;
                     42:                /* constant time for: x = ctr[i] ? 1 : 0 */
                     43:                x = ctr[i];
                     44:                x = (x | (x >> 4)) & 0xf;
                     45:                x = (x | (x >> 2)) & 0x3;
                     46:                x = (x | (x >> 1)) & 0x1;
                     47:                add *= (x^1);
                     48:        }
                     49: #endif
                     50: }
                     51:
                     52: void
                     53: aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
                     54: {
                     55:        x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
                     56: }
                     57:
                     58: void
                     59: aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
                     60: {
                     61:        memcpy(x->ctr, iv, AES_BLOCK_SIZE);
                     62: }
                     63:
                     64: void
                     65: aesctr_encrypt_bytes(aesctr_ctx *x,const u8 *m,u8 *c,u32 bytes)
                     66: {
                     67:        u32 n = 0;
                     68:        u8 buf[AES_BLOCK_SIZE];
                     69:
                     70:        while ((bytes--) > 0) {
                     71:                if (n == 0) {
                     72:                        rijndaelEncrypt(x->ek, x->rounds, x->ctr, buf);
                     73:                        aesctr_inc(x->ctr, AES_BLOCK_SIZE);
                     74:                }
                     75:                *(c++) = *(m++) ^ buf[n];
                     76:                n = (n + 1) % AES_BLOCK_SIZE;
                     77:        }
                     78: }