xref: /third_party/ffmpeg/libavutil/tea.c (revision cabdff1a) 
1/*
2 * A 32-bit implementation of the TEA algorithm
3 * Copyright (c) 2015 Vesselin Bontchev
4 *
5 * Loosely based on the implementation of David Wheeler and Roger Needham,
6 * https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm#Reference_code
7 *
8 * This file is part of FFmpeg.
9 *
10 * FFmpeg is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Lesser General Public
12 * License as published by the Free Software Foundation; either
13 * version 2.1 of the License, or (at your option) any later version.
14 *
15 * FFmpeg is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
18 * Lesser General Public License for more details.
19 *
20 * You should have received a copy of the GNU Lesser General Public
21 * License along with FFmpeg; if not, write to the Free Software
22 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23 */
24
25#include <string.h>
26#include "intreadwrite.h"
27#include "mem.h"
28#include "tea.h"
29
30typedef struct AVTEA {
31    uint32_t key[16];
32    int rounds;
33} AVTEA;
34
35struct AVTEA *av_tea_alloc(void)
36{
37    return av_mallocz(sizeof(struct AVTEA));
38}
39
40const int av_tea_size = sizeof(AVTEA);
41
42void av_tea_init(AVTEA *ctx, const uint8_t key[16], int rounds)
43{
44    int i;
45
46    for (i = 0; i < 4; i++)
47        ctx->key[i] = AV_RB32(key + (i << 2));
48
49    ctx->rounds = rounds;
50}
51
52static void tea_crypt_ecb(AVTEA *ctx, uint8_t *dst, const uint8_t *src,
53                          int decrypt, uint8_t *iv)
54{
55    uint32_t v0, v1;
56    int rounds = ctx->rounds;
57    uint32_t k0, k1, k2, k3;
58    k0 = ctx->key[0];
59    k1 = ctx->key[1];
60    k2 = ctx->key[2];
61    k3 = ctx->key[3];
62
63    v0 = AV_RB32(src);
64    v1 = AV_RB32(src + 4);
65
66    if (decrypt) {
67        int i;
68        uint32_t delta = 0x9E3779B9U, sum = delta * (rounds / 2);
69
70        for (i = 0; i < rounds / 2; i++) {
71            v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
72            v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
73            sum -= delta;
74        }
75        if (iv) {
76            v0 ^= AV_RB32(iv);
77            v1 ^= AV_RB32(iv + 4);
78            memcpy(iv, src, 8);
79        }
80    } else {
81        int i;
82        uint32_t sum = 0, delta = 0x9E3779B9U;
83
84        for (i = 0; i < rounds / 2; i++) {
85            sum += delta;
86            v0 += ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
87            v1 += ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
88        }
89    }
90
91    AV_WB32(dst, v0);
92    AV_WB32(dst + 4, v1);
93}
94
95void av_tea_crypt(AVTEA *ctx, uint8_t *dst, const uint8_t *src, int count,
96                  uint8_t *iv, int decrypt)
97{
98    int i;
99
100    if (decrypt) {
101        while (count--) {
102            tea_crypt_ecb(ctx, dst, src, decrypt, iv);
103
104            src   += 8;
105            dst   += 8;
106        }
107    } else {
108        while (count--) {
109            if (iv) {
110                for (i = 0; i < 8; i++)
111                    dst[i] = src[i] ^ iv[i];
112                tea_crypt_ecb(ctx, dst, dst, decrypt, NULL);
113                memcpy(iv, dst, 8);
114            } else {
115                tea_crypt_ecb(ctx, dst, src, decrypt, NULL);
116            }
117            src   += 8;
118            dst   += 8;
119        }
120    }
121}
122