1/*
2 * Decryption protocol handler
3 * Copyright (c) 2011 Martin Storsjo
4 *
5 * This file is part of Libav.
6 *
7 * Libav 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 * Libav 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 Libav; 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
32typedef 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
49static 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
55static 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
62static int crypto_open(URLContext *h, const char *uri, int flags)
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, NULL)) < 0) {
87        av_log(h, AV_LOG_ERROR, "Unable to open input\n");
88        goto err;
89    }
90    c->aes = av_mallocz(av_aes_size);
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
100err:
101    return ret;
102}
103
104static int crypto_read(URLContext *h, uint8_t *buf, int size)
105{
106    CryptoContext *c = h->priv_data;
107    int blocks;
108retry:
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
153static 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
162URLProtocol ff_crypto_protocol = {
163    .name            = "crypto",
164    .url_open        = crypto_open,
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