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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;
  34.     URLContext *hd;
  35.     uint8_t inbuffer [BLOCKSIZE*MAX_BUFFER_BLOCKS],
  36.             outbuffer[BLOCKSIZE*MAX_BUFFER_BLOCKS];
  37.     uint8_t *outptr;
  38.     int indata, indata_used, outdata;
  39.     int eof;
  40.     uint8_t *key;
  41.     int keylen;
  42.     uint8_t *iv;
  43.     int ivlen;
  44.     struct AVAES *aes;
  45. } CryptoContext;
  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;
  66.     CryptoContext *c = h->priv_data;
  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.  
  162. URLProtocol ff_crypto_protocol = {
  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,
  169.     .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,
  170. };
  171.