libavformat/crypto.c

   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 // encourage reads of 4096 bytes - 1 block is always retained.
  30 #define MAX_BUFFER_BLOCKS 257
  31 #define BLOCKSIZE 16
  32
  33 typedef struct CryptoContext {
  34     const AVClass *class;
  35     URLContext *hd;
  36     uint8_t inbuffer [BLOCKSIZE*MAX_BUFFER_BLOCKS],
  37             outbuffer[BLOCKSIZE*MAX_BUFFER_BLOCKS];
  38     uint8_t *outptr;
  39     int indata, indata_used, outdata;
  40     int64_t position;  // position in file - used in seek
  41     int flags;
  42     int eof;
  43     uint8_t *key;
  44     int keylen;
  45     uint8_t *iv;
  46     int ivlen;
  47     uint8_t *decrypt_key;
  48     int decrypt_keylen;
  49     uint8_t *decrypt_iv;
  50     int decrypt_ivlen;
  51     uint8_t *encrypt_key;
  52     int encrypt_keylen;
  53     uint8_t *encrypt_iv;
  54     int encrypt_ivlen;
  55     struct AVAES *aes_decrypt;
  56     struct AVAES *aes_encrypt;
  57
  58     uint8_t pad[BLOCKSIZE];
  59     int pad_len;
  60
  61 } CryptoContext;
  62
  63 #define OFFSET(x) offsetof(CryptoContext, x)
  64 #define D AV_OPT_FLAG_DECODING_PARAM
  65 #define E AV_OPT_FLAG_ENCODING_PARAM
  66 static const AVOption options[] = {
  67     {"key", "AES encryption/decryption key",                   OFFSET(key),         AV_OPT_TYPE_BINARY, .flags = D|E },
  68     {"iv",  "AES encryption/decryption initialization vector", OFFSET(iv),          AV_OPT_TYPE_BINARY, .flags = D|E },
  69     {"decryption_key", "AES decryption key",                   OFFSET(decrypt_key), AV_OPT_TYPE_BINARY, .flags = D },
  70     {"decryption_iv",  "AES decryption initialization vector", OFFSET(decrypt_iv),  AV_OPT_TYPE_BINARY, .flags = D },
  71     {"encryption_key", "AES encryption key",                   OFFSET(encrypt_key), AV_OPT_TYPE_BINARY, .flags = E },
  72     {"encryption_iv",  "AES encryption initialization vector", OFFSET(encrypt_iv),  AV_OPT_TYPE_BINARY, .flags = E },
  73     { NULL }
  74 };
  75
  76 static const AVClass crypto_class = {
  77     .class_name     = "crypto",
  78     .item_name      = av_default_item_name,
  79     .option         = options,
  80     .version        = LIBAVUTIL_VERSION_INT,
  81 };
  82
  83 static int set_aes_arg(CryptoContext *c, uint8_t **buf, int *buf_len,
  84                        uint8_t *default_buf, int default_buf_len,
  85                        const char *desc)
  86 {
  87     if (!*buf_len) {
  88         if (!default_buf_len) {
  89             av_log(c, AV_LOG_ERROR, "%s not set\n", desc);
  90             return AVERROR(EINVAL);
  91         } else if (default_buf_len != BLOCKSIZE) {
  92             av_log(c, AV_LOG_ERROR,
  93                    "invalid %s size (%d bytes, block size is %d)\n",
  94                    desc, default_buf_len, BLOCKSIZE);
  95             return AVERROR(EINVAL);
  96         }
  97         *buf = av_memdup(default_buf, default_buf_len);
  98         if (!*buf)
  99             return AVERROR(ENOMEM);
 100         *buf_len = default_buf_len;
 101     } else if (*buf_len != BLOCKSIZE) {
 102         av_log(c, AV_LOG_ERROR,
 103                "invalid %s size (%d bytes, block size is %d)\n",
 104                desc, *buf_len, BLOCKSIZE);
 105         return AVERROR(EINVAL);
 106     }
 107     return 0;
 108 }
 109
 110 static int crypto_open2(URLContext *h, const char *uri, int flags, AVDictionary **options)
 111 {
 112     const char *nested_url;
 113     int ret = 0;
 114     CryptoContext *c = h->priv_data;
 115     c->flags = flags;
 116
 117     if (!av_strstart(uri, "crypto+", &nested_url) &&
 118         !av_strstart(uri, "crypto:", &nested_url)) {
 119         av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
 120         ret = AVERROR(EINVAL);
 121         goto err;
 122     }
 123
 124     c->position = 0;
 125
 126     if (flags & AVIO_FLAG_READ) {
 127         if ((ret = set_aes_arg(c, &c->decrypt_key, &c->decrypt_keylen,
 128                                c->key, c->keylen, "decryption key")) < 0)
 129             goto err;
 130         if ((ret = set_aes_arg(c, &c->decrypt_iv, &c->decrypt_ivlen,
 131                                c->iv, c->ivlen, "decryption IV")) < 0)
 132             goto err;
 133     }
 134
 135     if (flags & AVIO_FLAG_WRITE) {
 136         if ((ret = set_aes_arg(c, &c->encrypt_key, &c->encrypt_keylen,
 137                                c->key, c->keylen, "encryption key")) < 0)
 138         if (ret < 0)
 139             goto err;
 140         if ((ret = set_aes_arg(c, &c->encrypt_iv, &c->encrypt_ivlen,
 141                                c->iv, c->ivlen, "encryption IV")) < 0)
 142             goto err;
 143     }
 144
 145     if ((ret = ffurl_open_whitelist(&c->hd, nested_url, flags,
 146                                     &h->interrupt_callback, options,
 147                                     h->protocol_whitelist, h->protocol_blacklist, h)) < 0) {
 148         av_log(h, AV_LOG_ERROR, "Unable to open resource: %s\n", nested_url);
 149         goto err;
 150     }
 151
 152     if (flags & AVIO_FLAG_READ) {
 153         c->aes_decrypt = av_aes_alloc();
 154         if (!c->aes_decrypt) {
 155             ret = AVERROR(ENOMEM);
 156             goto err;
 157         }
 158         ret = av_aes_init(c->aes_decrypt, c->decrypt_key, BLOCKSIZE*8, 1);
 159         if (ret < 0)
 160             goto err;
 161
 162         // pass back information about the context we openned
 163         if (c->hd->is_streamed)
 164             h->is_streamed = c->hd->is_streamed;
 165     }
 166
 167     if (flags & AVIO_FLAG_WRITE) {
 168         c->aes_encrypt = av_aes_alloc();
 169         if (!c->aes_encrypt) {
 170             ret = AVERROR(ENOMEM);
 171             goto err;
 172         }
 173         ret = av_aes_init(c->aes_encrypt, c->encrypt_key, BLOCKSIZE*8, 0);
 174         if (ret < 0)
 175             goto err;
 176         // for write, we must be streamed
 177         // - linear write only for crytpo aes-128-cbc
 178         h->is_streamed = 1;
 179     }
 180
 181     c->pad_len = 0;
 182
 183 err:
 184     return ret;
 185 }
 186
 187 static int crypto_read(URLContext *h, uint8_t *buf, int size)
 188 {
 189     CryptoContext *c = h->priv_data;
 190     int blocks;
 191 retry:
 192     if (c->outdata > 0) {
 193         size = FFMIN(size, c->outdata);
 194         memcpy(buf, c->outptr, size);
 195         c->outptr  += size;
 196         c->outdata -= size;
 197         c->position = c->position + size;
 198         return size;
 199     }
 200     // We avoid using the last block until we've found EOF,
 201     // since we'll remove PKCS7 padding at the end. So make
 202     // sure we've got at least 2 blocks, so we can decrypt
 203     // at least one.
 204     while (c->indata - c->indata_used < 2*BLOCKSIZE) {
 205         int n = ffurl_read(c->hd, c->inbuffer + c->indata,
 206                            sizeof(c->inbuffer) - c->indata);
 207         if (n <= 0) {
 208             c->eof = 1;
 209             break;
 210         }
 211         c->indata += n;
 212     }
 213     blocks = (c->indata - c->indata_used) / BLOCKSIZE;
 214     if (!blocks)
 215         return AVERROR_EOF;
 216     if (!c->eof)
 217         blocks--;
 218     av_aes_crypt(c->aes_decrypt, c->outbuffer, c->inbuffer + c->indata_used,
 219                  blocks, c->decrypt_iv, 1);
 220     c->outdata      = BLOCKSIZE * blocks;
 221     c->outptr       = c->outbuffer;
 222     c->indata_used += BLOCKSIZE * blocks;
 223     if (c->indata_used >= sizeof(c->inbuffer)/2) {
 224         memmove(c->inbuffer, c->inbuffer + c->indata_used,
 225                 c->indata - c->indata_used);
 226         c->indata     -= c->indata_used;
 227         c->indata_used = 0;
 228     }
 229     if (c->eof) {
 230         // Remove PKCS7 padding at the end
 231         int padding = c->outbuffer[c->outdata - 1];
 232         c->outdata -= padding;
 233     }
 234     goto retry;
 235 }
 236
 237 static int64_t crypto_seek(URLContext *h, int64_t pos, int whence)
 238 {
 239     CryptoContext *c = h->priv_data;
 240     int64_t block;
 241     int64_t newpos;
 242
 243     if (c->flags & AVIO_FLAG_WRITE) {
 244         av_log(h, AV_LOG_ERROR,
 245             "Crypto: seek not supported for write\r\n");
 246         /* seems the most appropriate error to return */
 247         return AVERROR(ESPIPE);
 248     }
 249
 250     // reset eof, else we won't read it correctly if we already hit eof.
 251     c->eof = 0;
 252
 253     switch (whence) {
 254     case SEEK_SET:
 255         break;
 256     case SEEK_CUR:
 257         pos = pos + c->position;
 258         break;
 259     case SEEK_END: {
 260         int64_t newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
 261         if (newpos < 0) {
 262             av_log(h, AV_LOG_ERROR,
 263                 "Crypto: seek_end - can't get file size (pos=%lld)\r\n", (long long int)pos);
 264             return newpos;
 265         }
 266         pos = newpos - pos;
 267         }
 268         break;
 269     case AVSEEK_SIZE: {
 270         int64_t newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
 271         return newpos;
 272         }
 273         break;
 274     default:
 275         av_log(h, AV_LOG_ERROR,
 276             "Crypto: no support for seek where 'whence' is %d\r\n", whence);
 277         return AVERROR(EINVAL);
 278     }
 279
 280     c->outdata = 0;
 281     c->indata = 0;
 282     c->indata_used = 0;
 283     c->outptr = c->outbuffer;
 284
 285     // identify the block containing the IV for the
 286     // next block we will decrypt
 287     block = pos/BLOCKSIZE;
 288     if (block == 0) {
 289         // restore the iv to the seed one - this is the iv for the FIRST block
 290         memcpy( c->decrypt_iv, c->iv, c->ivlen );
 291         c->position = 0;
 292     } else {
 293         // else, go back one block - we will get av_cyrpt to read this block
 294         // which it will then store use as the iv.
 295         // note that the DECRYPTED result will not be correct,
 296         // but will be discarded
 297         block--;
 298         c->position = (block * BLOCKSIZE);
 299     }
 300
 301     newpos = ffurl_seek( c->hd, c->position, SEEK_SET );
 302     if (newpos < 0) {
 303         av_log(h, AV_LOG_ERROR,
 304             "Crypto: nested protocol no support for seek or seek failed\n");
 305         return newpos;
 306     }
 307
 308     // read and discard from here up to required position
 309     // (which will set the iv correctly to it).
 310     if (pos - c->position) {
 311         uint8_t buff[BLOCKSIZE*2]; // maximum size of pos-c->position
 312         int len = pos - c->position;
 313         int res;
 314
 315         while (len > 0) {
 316             // note: this may not return all the bytes first time
 317             res = crypto_read(h, buff, len);
 318             if (res < 0)
 319                 break;
 320             len -= res;
 321         }
 322
 323         // if we did not get all the bytes
 324         if (len != 0) {
 325             char errbuf[100] = "unknown error";
 326             av_strerror(res, errbuf, sizeof(errbuf));
 327             av_log(h, AV_LOG_ERROR,
 328                 "Crypto: discard read did not get all the bytes (%d remain) - read returned (%d)-%s\n",
 329                 len, res, errbuf);
 330             return AVERROR(EINVAL);
 331         }
 332     }
 333
 334     return c->position;
 335 }
 336
 337 static int crypto_write(URLContext *h, const unsigned char *buf, int size)
 338 {
 339     CryptoContext *c = h->priv_data;
 340     int total_size, blocks, pad_len, out_size;
 341     uint8_t *out_buf;
 342     int ret = 0;
 343
 344     total_size = size + c->pad_len;
 345     pad_len = total_size % BLOCKSIZE;
 346     out_size = total_size - pad_len;
 347     blocks = out_size / BLOCKSIZE;
 348
 349     if (out_size) {
 350         out_buf = av_malloc(out_size);
 351         if (!out_buf)
 352             return AVERROR(ENOMEM);
 353
 354         if (c->pad_len) {
 355             memcpy(&c->pad[c->pad_len], buf, BLOCKSIZE - c->pad_len);
 356             av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);
 357             blocks--;
 358         }
 359
 360         av_aes_crypt(c->aes_encrypt, &out_buf[c->pad_len ? BLOCKSIZE : 0],
 361                              &buf[c->pad_len ? BLOCKSIZE - c->pad_len: 0],
 362                              blocks, c->encrypt_iv, 0);
 363
 364         ret = ffurl_write(c->hd, out_buf, out_size);
 365         av_free(out_buf);
 366         if (ret < 0)
 367             return ret;
 368
 369         memcpy(c->pad, &buf[size - pad_len], pad_len);
 370     } else
 371         memcpy(&c->pad[c->pad_len], buf, size);
 372
 373     c->pad_len = pad_len;
 374
 375     return size;
 376 }
 377
 378 static int crypto_close(URLContext *h)
 379 {
 380     CryptoContext *c = h->priv_data;
 381     uint8_t out_buf[BLOCKSIZE];
 382     int ret, pad;
 383
 384     if (c->aes_encrypt) {
 385         pad = BLOCKSIZE - c->pad_len;
 386         memset(&c->pad[c->pad_len], pad, pad);
 387         av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);
 388         if ((ret =  ffurl_write(c->hd, out_buf, BLOCKSIZE)) < 0)
 389             return ret;
 390     }
 391
 392     if (c->hd)
 393         ffurl_close(c->hd);
 394     av_freep(&c->aes_decrypt);
 395     av_freep(&c->aes_encrypt);
 396     return 0;
 397 }
 398
 399 const URLProtocol ff_crypto_protocol = {
 400     .name            = "crypto",
 401     .url_open2       = crypto_open2,
 402     .url_seek        = crypto_seek,
 403     .url_read        = crypto_read,
 404     .url_write       = crypto_write,
 405     .url_close       = crypto_close,
 406     .priv_data_size  = sizeof(CryptoContext),
 407     .priv_data_class = &crypto_class,
 408     .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,
 409 };