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 "libavutil/aes.h"
  23 #include "libavutil/avstring.h"
  24 #include "libavutil/mem.h"
  25 #include "libavutil/opt.h"
  26 #include "url.h"
  27
  28 // encourage reads of 4096 bytes - 1 block is always retained.
  29 #define MAX_BUFFER_BLOCKS 257
  30 #define BLOCKSIZE 16
  31
  32 typedef struct CryptoContext {
  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     int64_t position;  // position in file - used in seek
  40     int flags;
  41     int eof;
  42     uint8_t *key;
  43     int keylen;
  44     uint8_t *iv;
  45     int ivlen;
  46     uint8_t *decrypt_key;
  47     int decrypt_keylen;
  48     uint8_t *decrypt_iv;
  49     int decrypt_ivlen;
  50     uint8_t *encrypt_key;
  51     int encrypt_keylen;
  52     uint8_t *encrypt_iv;
  53     int encrypt_ivlen;
  54     struct AVAES *aes_decrypt;
  55     struct AVAES *aes_encrypt;
  56     uint8_t *write_buf;
  57     unsigned int write_buf_size;
  58     uint8_t pad[BLOCKSIZE];
  59     int pad_len;
  60 } CryptoContext;
  61
  62 #define OFFSET(x) offsetof(CryptoContext, x)
  63 #define D AV_OPT_FLAG_DECODING_PARAM
  64 #define E AV_OPT_FLAG_ENCODING_PARAM
  65 static const AVOption crypto_options[] = {
  66     {"key", "AES encryption/decryption key",                   OFFSET(key),         AV_OPT_TYPE_BINARY, .flags = D|E },
  67     {"iv",  "AES encryption/decryption initialization vector", OFFSET(iv),          AV_OPT_TYPE_BINARY, .flags = D|E },
  68     {"decryption_key", "AES decryption key",                   OFFSET(decrypt_key), AV_OPT_TYPE_BINARY, .flags = D },
  69     {"decryption_iv",  "AES decryption initialization vector", OFFSET(decrypt_iv),  AV_OPT_TYPE_BINARY, .flags = D },
  70     {"encryption_key", "AES encryption key",                   OFFSET(encrypt_key), AV_OPT_TYPE_BINARY, .flags = E },
  71     {"encryption_iv",  "AES encryption initialization vector", OFFSET(encrypt_iv),  AV_OPT_TYPE_BINARY, .flags = E },
  72     { NULL }
  73 };
  74
  75 static const AVClass crypto_class = {
  76     .class_name     = "crypto",
  77     .item_name      = av_default_item_name,
  78     .option         = crypto_options,
  79     .version        = LIBAVUTIL_VERSION_INT,
  80 };
  81
  82 static int set_aes_arg(URLContext *h, uint8_t **buf, int *buf_len,
  83                        uint8_t *default_buf, int default_buf_len,
  84                        const char *desc)
  85 {
  86     if (!*buf_len) {
  87         if (!default_buf_len) {
  88             av_log(h, AV_LOG_ERROR, "%s not set\n", desc);
  89             return AVERROR(EINVAL);
  90         } else if (default_buf_len != BLOCKSIZE) {
  91             av_log(h, AV_LOG_ERROR,
  92                    "invalid %s size (%d bytes, block size is %d)\n",
  93                    desc, default_buf_len, BLOCKSIZE);
  94             return AVERROR(EINVAL);
  95         }
  96         *buf = av_memdup(default_buf, default_buf_len);
  97         if (!*buf)
  98             return AVERROR(ENOMEM);
  99         *buf_len = default_buf_len;
 100     } else if (*buf_len != BLOCKSIZE) {
 101         av_log(h, AV_LOG_ERROR,
 102                "invalid %s size (%d bytes, block size is %d)\n",
 103                desc, *buf_len, BLOCKSIZE);
 104         return AVERROR(EINVAL);
 105     }
 106     return 0;
 107 }
 108
 109 static int crypto_open2(URLContext *h, const char *uri, int flags, AVDictionary **options)
 110 {
 111     const char *nested_url;
 112     int ret = 0;
 113     CryptoContext *c = h->priv_data;
 114     c->flags = flags;
 115
 116     if (!av_strstart(uri, "crypto+", &nested_url) &&
 117         !av_strstart(uri, "crypto:", &nested_url)) {
 118         av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
 119         ret = AVERROR(EINVAL);
 120         goto err;
 121     }
 122
 123     if (flags & AVIO_FLAG_READ) {
 124         if ((ret = set_aes_arg(h, &c->decrypt_key, &c->decrypt_keylen,
 125                                c->key, c->keylen, "decryption key")) < 0)
 126             goto err;
 127         if ((ret = set_aes_arg(h, &c->decrypt_iv, &c->decrypt_ivlen,
 128                                c->iv, c->ivlen, "decryption IV")) < 0)
 129             goto err;
 130     }
 131
 132     if (flags & AVIO_FLAG_WRITE) {
 133         if ((ret = set_aes_arg(h, &c->encrypt_key, &c->encrypt_keylen,
 134                                c->key, c->keylen, "encryption key")) < 0)
 135         if (ret < 0)
 136             goto err;
 137         if ((ret = set_aes_arg(h, &c->encrypt_iv, &c->encrypt_ivlen,
 138                                c->iv, c->ivlen, "encryption IV")) < 0)
 139             goto err;
 140     }
 141
 142     if ((ret = ffurl_open_whitelist(&c->hd, nested_url, flags,
 143                                     &h->interrupt_callback, options,
 144                                     h->protocol_whitelist, h->protocol_blacklist, h)) < 0) {
 145         av_log(h, AV_LOG_ERROR, "Unable to open resource: %s\n", nested_url);
 146         goto err;
 147     }
 148
 149     if (flags & AVIO_FLAG_READ) {
 150         c->aes_decrypt = av_aes_alloc();
 151         if (!c->aes_decrypt) {
 152             ret = AVERROR(ENOMEM);
 153             goto err;
 154         }
 155         ret = av_aes_init(c->aes_decrypt, c->decrypt_key, BLOCKSIZE * 8, 1);
 156         if (ret < 0)
 157             goto err;
 158
 159         // pass back information about the context we opened
 160         if (c->hd->is_streamed)
 161             h->is_streamed = c->hd->is_streamed;
 162     }
 163
 164     if (flags & AVIO_FLAG_WRITE) {
 165         c->aes_encrypt = av_aes_alloc();
 166         if (!c->aes_encrypt) {
 167             ret = AVERROR(ENOMEM);
 168             goto err;
 169         }
 170         ret = av_aes_init(c->aes_encrypt, c->encrypt_key, BLOCKSIZE * 8, 0);
 171         if (ret < 0)
 172             goto err;
 173         // for write, we must be streamed
 174         // - linear write only for crypto aes-128-cbc
 175         h->is_streamed = 1;
 176     }
 177
 178 err:
 179     return ret;
 180 }
 181
 182 static int crypto_read(URLContext *h, uint8_t *buf, int size)
 183 {
 184     CryptoContext *c = h->priv_data;
 185     int blocks;
 186 retry:
 187     if (c->outdata > 0) {
 188         size = FFMIN(size, c->outdata);
 189         memcpy(buf, c->outptr, size);
 190         c->outptr  += size;
 191         c->outdata -= size;
 192         c->position = c->position + size;
 193         return size;
 194     }
 195     // We avoid using the last block until we've found EOF,
 196     // since we'll remove PKCS7 padding at the end. So make
 197     // sure we've got at least 2 blocks, so we can decrypt
 198     // at least one.
 199     while (c->indata - c->indata_used < 2*BLOCKSIZE) {
 200         int n = ffurl_read(c->hd, c->inbuffer + c->indata,
 201                            sizeof(c->inbuffer) - c->indata);
 202         if (n <= 0) {
 203             c->eof = 1;
 204             break;
 205         }
 206         c->indata += n;
 207     }
 208     blocks = (c->indata - c->indata_used) / BLOCKSIZE;
 209     if (!blocks)
 210         return AVERROR_EOF;
 211     if (!c->eof)
 212         blocks--;
 213     av_aes_crypt(c->aes_decrypt, c->outbuffer, c->inbuffer + c->indata_used,
 214                  blocks, c->decrypt_iv, 1);
 215     c->outdata      = BLOCKSIZE * blocks;
 216     c->outptr       = c->outbuffer;
 217     c->indata_used += BLOCKSIZE * blocks;
 218     if (c->indata_used >= sizeof(c->inbuffer)/2) {
 219         memmove(c->inbuffer, c->inbuffer + c->indata_used,
 220                 c->indata - c->indata_used);
 221         c->indata     -= c->indata_used;
 222         c->indata_used = 0;
 223     }
 224     if (c->eof) {
 225         // Remove PKCS7 padding at the end
 226         int padding = c->outbuffer[c->outdata - 1];
 227         c->outdata -= padding;
 228     }
 229     goto retry;
 230 }
 231
 232 static int64_t crypto_seek(URLContext *h, int64_t pos, int whence)
 233 {
 234     CryptoContext *c = h->priv_data;
 235     int64_t block;
 236     int64_t newpos;
 237
 238     if (c->flags & AVIO_FLAG_WRITE) {
 239         av_log(h, AV_LOG_ERROR,
 240             "Crypto: seek not supported for write\r\n");
 241         /* seems the most appropriate error to return */
 242         return AVERROR(ESPIPE);
 243     }
 244
 245     // reset eof, else we won't read it correctly if we already hit eof.
 246     c->eof = 0;
 247
 248     switch (whence) {
 249     case SEEK_SET:
 250         break;
 251     case SEEK_CUR:
 252         pos = pos + c->position;
 253         break;
 254     case SEEK_END:
 255         newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
 256         if (newpos < 0) {
 257             av_log(h, AV_LOG_ERROR,
 258                 "Crypto: seek_end - can't get file size (pos=%"PRId64")\r\n", pos);
 259             return newpos;
 260         }
 261         pos = newpos - pos;
 262         break;
 263     case AVSEEK_SIZE:
 264         return ffurl_seek( c->hd, pos, AVSEEK_SIZE );
 265     default:
 266         av_log(h, AV_LOG_ERROR,
 267             "Crypto: no support for seek where 'whence' is %d\r\n", whence);
 268         return AVERROR(EINVAL);
 269     }
 270
 271     c->outdata = 0;
 272     c->indata = 0;
 273     c->indata_used = 0;
 274     c->outptr = c->outbuffer;
 275
 276     // identify the block containing the IV for the
 277     // next block we will decrypt
 278     block = pos/BLOCKSIZE;
 279     if (block == 0) {
 280         // restore the iv to the seed one - this is the iv for the FIRST block
 281         memcpy( c->decrypt_iv, c->iv, c->ivlen );
 282         c->position = 0;
 283     } else {
 284         // else, go back one block - we will get av_cyrpt to read this block
 285         // which it will then store use as the iv.
 286         // note that the DECRYPTED result will not be correct,
 287         // but will be discarded
 288         block--;
 289         c->position = (block * BLOCKSIZE);
 290     }
 291
 292     newpos = ffurl_seek( c->hd, c->position, SEEK_SET );
 293     if (newpos < 0) {
 294         av_log(h, AV_LOG_ERROR,
 295             "Crypto: nested protocol no support for seek or seek failed\n");
 296         return newpos;
 297     }
 298
 299     // read and discard from here up to required position
 300     // (which will set the iv correctly to it).
 301     if (pos - c->position) {
 302         uint8_t buff[BLOCKSIZE*2]; // maximum size of pos-c->position
 303         int len = pos - c->position;
 304         int res;
 305
 306         while (len > 0) {
 307             // note: this may not return all the bytes first time
 308             res = crypto_read(h, buff, len);
 309             if (res < 0)
 310                 break;
 311             len -= res;
 312         }
 313
 314         // if we did not get all the bytes
 315         if (len != 0) {
 316             av_log(h, AV_LOG_ERROR,
 317                 "Crypto: discard read did not get all the bytes (%d remain) - read returned (%d)-%s\n",
 318                 len, res, av_err2str(res));
 319             return AVERROR(EINVAL);
 320         }
 321     }
 322
 323     return c->position;
 324 }
 325
 326 static int crypto_write(URLContext *h, const unsigned char *buf, int size)
 327 {
 328     CryptoContext *c = h->priv_data;
 329     int total_size, blocks, pad_len, out_size;
 330     int ret = 0;
 331
 332     total_size = size + c->pad_len;
 333     pad_len = total_size % BLOCKSIZE;
 334     out_size = total_size - pad_len;
 335     blocks = out_size / BLOCKSIZE;
 336
 337     if (out_size) {
 338         av_fast_malloc(&c->write_buf, &c->write_buf_size, out_size);
 339
 340         if (!c->write_buf)
 341             return AVERROR(ENOMEM);
 342
 343         if (c->pad_len) {
 344             memcpy(&c->pad[c->pad_len], buf, BLOCKSIZE - c->pad_len);
 345             av_aes_crypt(c->aes_encrypt, c->write_buf, c->pad, 1, c->encrypt_iv, 0);
 346             blocks--;
 347         }
 348
 349         av_aes_crypt(c->aes_encrypt,
 350                      &c->write_buf[c->pad_len ? BLOCKSIZE : 0],
 351                      &buf[c->pad_len ? BLOCKSIZE - c->pad_len : 0],
 352                      blocks, c->encrypt_iv, 0);
 353
 354         ret = ffurl_write(c->hd, c->write_buf, out_size);
 355         if (ret < 0)
 356             return ret;
 357
 358         memcpy(c->pad, &buf[size - pad_len], pad_len);
 359     } else
 360         memcpy(&c->pad[c->pad_len], buf, size);
 361
 362     c->pad_len = pad_len;
 363
 364     return size;
 365 }
 366
 367 static int crypto_close(URLContext *h)
 368 {
 369     CryptoContext *c = h->priv_data;
 370     int ret = 0;
 371
 372     if (c->aes_encrypt) {
 373         uint8_t out_buf[BLOCKSIZE];
 374         int pad = BLOCKSIZE - c->pad_len;
 375
 376         memset(&c->pad[c->pad_len], pad, pad);
 377         av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);
 378         ret = ffurl_write(c->hd, out_buf, BLOCKSIZE);
 379     }
 380
 381     ffurl_closep(&c->hd);
 382     av_freep(&c->aes_decrypt);
 383     av_freep(&c->aes_encrypt);
 384     av_freep(&c->write_buf);
 385     return ret;
 386 }
 387
 388 const URLProtocol ff_crypto_protocol = {
 389     .name            = "crypto",
 390     .url_open2       = crypto_open2,
 391     .url_seek        = crypto_seek,
 392     .url_read        = crypto_read,
 393     .url_write       = crypto_write,
 394     .url_close       = crypto_close,
 395     .priv_data_size  = sizeof(CryptoContext),
 396     .priv_data_class = &crypto_class,
 397     .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,
 398 };