xref: /third_party/ffmpeg/libavformat/crypto.c (revision cabdff1a) 
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
33typedef 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    uint8_t *write_buf;
58    unsigned int write_buf_size;
59    uint8_t pad[BLOCKSIZE];
60    int pad_len;
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
66static 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
76static 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
83static int set_aes_arg(URLContext *h, 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(h, AV_LOG_ERROR, "%s not set\n", desc);
90            return AVERROR(EINVAL);
91        } else if (default_buf_len != BLOCKSIZE) {
92            av_log(h, 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(h, 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
110static 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    if (flags & AVIO_FLAG_READ) {
125        if ((ret = set_aes_arg(h, &c->decrypt_key, &c->decrypt_keylen,
126                               c->key, c->keylen, "decryption key")) < 0)
127            goto err;
128        if ((ret = set_aes_arg(h, &c->decrypt_iv, &c->decrypt_ivlen,
129                               c->iv, c->ivlen, "decryption IV")) < 0)
130            goto err;
131    }
132
133    if (flags & AVIO_FLAG_WRITE) {
134        if ((ret = set_aes_arg(h, &c->encrypt_key, &c->encrypt_keylen,
135                               c->key, c->keylen, "encryption key")) < 0)
136        if (ret < 0)
137            goto err;
138        if ((ret = set_aes_arg(h, &c->encrypt_iv, &c->encrypt_ivlen,
139                               c->iv, c->ivlen, "encryption IV")) < 0)
140            goto err;
141    }
142
143    if ((ret = ffurl_open_whitelist(&c->hd, nested_url, flags,
144                                    &h->interrupt_callback, options,
145                                    h->protocol_whitelist, h->protocol_blacklist, h)) < 0) {
146        av_log(h, AV_LOG_ERROR, "Unable to open resource: %s\n", nested_url);
147        goto err;
148    }
149
150    if (flags & AVIO_FLAG_READ) {
151        c->aes_decrypt = av_aes_alloc();
152        if (!c->aes_decrypt) {
153            ret = AVERROR(ENOMEM);
154            goto err;
155        }
156        ret = av_aes_init(c->aes_decrypt, c->decrypt_key, BLOCKSIZE * 8, 1);
157        if (ret < 0)
158            goto err;
159
160        // pass back information about the context we openned
161        if (c->hd->is_streamed)
162            h->is_streamed = c->hd->is_streamed;
163    }
164
165    if (flags & AVIO_FLAG_WRITE) {
166        c->aes_encrypt = av_aes_alloc();
167        if (!c->aes_encrypt) {
168            ret = AVERROR(ENOMEM);
169            goto err;
170        }
171        ret = av_aes_init(c->aes_encrypt, c->encrypt_key, BLOCKSIZE * 8, 0);
172        if (ret < 0)
173            goto err;
174        // for write, we must be streamed
175        // - linear write only for crytpo aes-128-cbc
176        h->is_streamed = 1;
177    }
178
179err:
180    return ret;
181}
182
183static int crypto_read(URLContext *h, uint8_t *buf, int size)
184{
185    CryptoContext *c = h->priv_data;
186    int blocks;
187retry:
188    if (c->outdata > 0) {
189        size = FFMIN(size, c->outdata);
190        memcpy(buf, c->outptr, size);
191        c->outptr  += size;
192        c->outdata -= size;
193        c->position = c->position + size;
194        return size;
195    }
196    // We avoid using the last block until we've found EOF,
197    // since we'll remove PKCS7 padding at the end. So make
198    // sure we've got at least 2 blocks, so we can decrypt
199    // at least one.
200    while (c->indata - c->indata_used < 2*BLOCKSIZE) {
201        int n = ffurl_read(c->hd, c->inbuffer + c->indata,
202                           sizeof(c->inbuffer) - c->indata);
203        if (n <= 0) {
204            c->eof = 1;
205            break;
206        }
207        c->indata += n;
208    }
209    blocks = (c->indata - c->indata_used) / BLOCKSIZE;
210    if (!blocks)
211        return AVERROR_EOF;
212    if (!c->eof)
213        blocks--;
214    av_aes_crypt(c->aes_decrypt, c->outbuffer, c->inbuffer + c->indata_used,
215                 blocks, c->decrypt_iv, 1);
216    c->outdata      = BLOCKSIZE * blocks;
217    c->outptr       = c->outbuffer;
218    c->indata_used += BLOCKSIZE * blocks;
219    if (c->indata_used >= sizeof(c->inbuffer)/2) {
220        memmove(c->inbuffer, c->inbuffer + c->indata_used,
221                c->indata - c->indata_used);
222        c->indata     -= c->indata_used;
223        c->indata_used = 0;
224    }
225    if (c->eof) {
226        // Remove PKCS7 padding at the end
227        int padding = c->outbuffer[c->outdata - 1];
228        c->outdata -= padding;
229    }
230    goto retry;
231}
232
233static int64_t crypto_seek(URLContext *h, int64_t pos, int whence)
234{
235    CryptoContext *c = h->priv_data;
236    int64_t block;
237    int64_t newpos;
238
239    if (c->flags & AVIO_FLAG_WRITE) {
240        av_log(h, AV_LOG_ERROR,
241            "Crypto: seek not supported for write\r\n");
242        /* seems the most appropriate error to return */
243        return AVERROR(ESPIPE);
244    }
245
246    // reset eof, else we won't read it correctly if we already hit eof.
247    c->eof = 0;
248
249    switch (whence) {
250    case SEEK_SET:
251        break;
252    case SEEK_CUR:
253        pos = pos + c->position;
254        break;
255    case SEEK_END:
256        newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
257        if (newpos < 0) {
258            av_log(h, AV_LOG_ERROR,
259                "Crypto: seek_end - can't get file size (pos=%lld)\r\n", (long long int)pos);
260            return newpos;
261        }
262        pos = newpos - pos;
263        break;
264    case AVSEEK_SIZE:
265        return ffurl_seek( c->hd, pos, AVSEEK_SIZE );
266    default:
267        av_log(h, AV_LOG_ERROR,
268            "Crypto: no support for seek where 'whence' is %d\r\n", whence);
269        return AVERROR(EINVAL);
270    }
271
272    c->outdata = 0;
273    c->indata = 0;
274    c->indata_used = 0;
275    c->outptr = c->outbuffer;
276
277    // identify the block containing the IV for the
278    // next block we will decrypt
279    block = pos/BLOCKSIZE;
280    if (block == 0) {
281        // restore the iv to the seed one - this is the iv for the FIRST block
282        memcpy( c->decrypt_iv, c->iv, c->ivlen );
283        c->position = 0;
284    } else {
285        // else, go back one block - we will get av_cyrpt to read this block
286        // which it will then store use as the iv.
287        // note that the DECRYPTED result will not be correct,
288        // but will be discarded
289        block--;
290        c->position = (block * BLOCKSIZE);
291    }
292
293    newpos = ffurl_seek( c->hd, c->position, SEEK_SET );
294    if (newpos < 0) {
295        av_log(h, AV_LOG_ERROR,
296            "Crypto: nested protocol no support for seek or seek failed\n");
297        return newpos;
298    }
299
300    // read and discard from here up to required position
301    // (which will set the iv correctly to it).
302    if (pos - c->position) {
303        uint8_t buff[BLOCKSIZE*2]; // maximum size of pos-c->position
304        int len = pos - c->position;
305        int res;
306
307        while (len > 0) {
308            // note: this may not return all the bytes first time
309            res = crypto_read(h, buff, len);
310            if (res < 0)
311                break;
312            len -= res;
313        }
314
315        // if we did not get all the bytes
316        if (len != 0) {
317            char errbuf[100] = "unknown error";
318            av_strerror(res, errbuf, sizeof(errbuf));
319            av_log(h, AV_LOG_ERROR,
320                "Crypto: discard read did not get all the bytes (%d remain) - read returned (%d)-%s\n",
321                len, res, errbuf);
322            return AVERROR(EINVAL);
323        }
324    }
325
326    return c->position;
327}
328
329static int crypto_write(URLContext *h, const unsigned char *buf, int size)
330{
331    CryptoContext *c = h->priv_data;
332    int total_size, blocks, pad_len, out_size;
333    int ret = 0;
334
335    total_size = size + c->pad_len;
336    pad_len = total_size % BLOCKSIZE;
337    out_size = total_size - pad_len;
338    blocks = out_size / BLOCKSIZE;
339
340    if (out_size) {
341        av_fast_malloc(&c->write_buf, &c->write_buf_size, out_size);
342
343        if (!c->write_buf)
344            return AVERROR(ENOMEM);
345
346        if (c->pad_len) {
347            memcpy(&c->pad[c->pad_len], buf, BLOCKSIZE - c->pad_len);
348            av_aes_crypt(c->aes_encrypt, c->write_buf, c->pad, 1, c->encrypt_iv, 0);
349            blocks--;
350        }
351
352        av_aes_crypt(c->aes_encrypt,
353                     &c->write_buf[c->pad_len ? BLOCKSIZE : 0],
354                     &buf[c->pad_len ? BLOCKSIZE - c->pad_len : 0],
355                     blocks, c->encrypt_iv, 0);
356
357        ret = ffurl_write(c->hd, c->write_buf, out_size);
358        if (ret < 0)
359            return ret;
360
361        memcpy(c->pad, &buf[size - pad_len], pad_len);
362    } else
363        memcpy(&c->pad[c->pad_len], buf, size);
364
365    c->pad_len = pad_len;
366
367    return size;
368}
369
370static int crypto_close(URLContext *h)
371{
372    CryptoContext *c = h->priv_data;
373    int ret = 0;
374
375    if (c->aes_encrypt) {
376        uint8_t out_buf[BLOCKSIZE];
377        int pad = BLOCKSIZE - c->pad_len;
378
379        memset(&c->pad[c->pad_len], pad, pad);
380        av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);
381        ret = ffurl_write(c->hd, out_buf, BLOCKSIZE);
382    }
383
384    ffurl_closep(&c->hd);
385    av_freep(&c->aes_decrypt);
386    av_freep(&c->aes_encrypt);
387    av_freep(&c->write_buf);
388    return ret;
389}
390
391const URLProtocol ff_crypto_protocol = {
392    .name            = "crypto",
393    .url_open2       = crypto_open2,
394    .url_seek        = crypto_seek,
395    .url_read        = crypto_read,
396    .url_write       = crypto_write,
397    .url_close       = crypto_close,
398    .priv_data_size  = sizeof(CryptoContext),
399    .priv_data_class = &crypto_class,
400    .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,
401};
402