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crypto.c
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1 /*
2  * Decryption protocol handler
3  * Copyright (c) 2011 Martin Storsjo
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #include "avformat.h"
23 #include "libavutil/aes.h"
24 #include "libavutil/avstring.h"
25 #include "libavutil/opt.h"
26 #include "internal.h"
27 #include "url.h"
28 
29 #define MAX_BUFFER_BLOCKS 150
30 #define BLOCKSIZE 16
31 
32 typedef struct {
33  const AVClass *class;
36  outbuffer[BLOCKSIZE*MAX_BUFFER_BLOCKS];
38  int indata, indata_used, outdata;
39  int eof;
41  int keylen;
43  int ivlen;
44  struct AVAES *aes;
46 
47 #define OFFSET(x) offsetof(CryptoContext, x)
48 #define D AV_OPT_FLAG_DECODING_PARAM
49 static const AVOption options[] = {
50  {"key", "AES decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, .flags = D },
51  {"iv", "AES decryption initialization vector", OFFSET(iv), AV_OPT_TYPE_BINARY, .flags = D },
52  { NULL }
53 };
54 
55 static const AVClass crypto_class = {
56  .class_name = "crypto",
57  .item_name = av_default_item_name,
58  .option = options,
59  .version = LIBAVUTIL_VERSION_INT,
60 };
61 
62 static int crypto_open2(URLContext *h, const char *uri, int flags, AVDictionary **options)
63 {
64  const char *nested_url;
65  int ret = 0;
67 
68  if (!av_strstart(uri, "crypto+", &nested_url) &&
69  !av_strstart(uri, "crypto:", &nested_url)) {
70  av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
71  ret = AVERROR(EINVAL);
72  goto err;
73  }
74 
75  if (c->keylen < BLOCKSIZE || c->ivlen < BLOCKSIZE) {
76  av_log(h, AV_LOG_ERROR, "Key or IV not set\n");
77  ret = AVERROR(EINVAL);
78  goto err;
79  }
80  if (flags & AVIO_FLAG_WRITE) {
81  av_log(h, AV_LOG_ERROR, "Only decryption is supported currently\n");
82  ret = AVERROR(ENOSYS);
83  goto err;
84  }
85  if ((ret = ffurl_open(&c->hd, nested_url, AVIO_FLAG_READ,
86  &h->interrupt_callback, options)) < 0) {
87  av_log(h, AV_LOG_ERROR, "Unable to open input\n");
88  goto err;
89  }
90  c->aes = av_aes_alloc();
91  if (!c->aes) {
92  ret = AVERROR(ENOMEM);
93  goto err;
94  }
95 
96  av_aes_init(c->aes, c->key, 128, 1);
97 
98  h->is_streamed = 1;
99 
100 err:
101  return ret;
102 }
103 
104 static int crypto_read(URLContext *h, uint8_t *buf, int size)
105 {
106  CryptoContext *c = h->priv_data;
107  int blocks;
108 retry:
109  if (c->outdata > 0) {
110  size = FFMIN(size, c->outdata);
111  memcpy(buf, c->outptr, size);
112  c->outptr += size;
113  c->outdata -= size;
114  return size;
115  }
116  // We avoid using the last block until we've found EOF,
117  // since we'll remove PKCS7 padding at the end. So make
118  // sure we've got at least 2 blocks, so we can decrypt
119  // at least one.
120  while (c->indata - c->indata_used < 2*BLOCKSIZE) {
121  int n = ffurl_read(c->hd, c->inbuffer + c->indata,
122  sizeof(c->inbuffer) - c->indata);
123  if (n <= 0) {
124  c->eof = 1;
125  break;
126  }
127  c->indata += n;
128  }
129  blocks = (c->indata - c->indata_used) / BLOCKSIZE;
130  if (!blocks)
131  return AVERROR_EOF;
132  if (!c->eof)
133  blocks--;
134  av_aes_crypt(c->aes, c->outbuffer, c->inbuffer + c->indata_used, blocks,
135  c->iv, 1);
136  c->outdata = BLOCKSIZE * blocks;
137  c->outptr = c->outbuffer;
138  c->indata_used += BLOCKSIZE * blocks;
139  if (c->indata_used >= sizeof(c->inbuffer)/2) {
140  memmove(c->inbuffer, c->inbuffer + c->indata_used,
141  c->indata - c->indata_used);
142  c->indata -= c->indata_used;
143  c->indata_used = 0;
144  }
145  if (c->eof) {
146  // Remove PKCS7 padding at the end
147  int padding = c->outbuffer[c->outdata - 1];
148  c->outdata -= padding;
149  }
150  goto retry;
151 }
152 
153 static int crypto_close(URLContext *h)
154 {
155  CryptoContext *c = h->priv_data;
156  if (c->hd)
157  ffurl_close(c->hd);
158  av_freep(&c->aes);
159  return 0;
160 }
161 
163  .name = "crypto",
164  .url_open2 = crypto_open2,
165  .url_read = crypto_read,
166  .url_close = crypto_close,
167  .priv_data_size = sizeof(CryptoContext),
168  .priv_data_class = &crypto_class,
170 };