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ffmpeg/libavformat/crypto.c

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/*
* Decryption protocol handler
* Copyright (c) 2011 Martin Storsjo
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "avformat.h"
#include "libavutil/aes.h"
#include "libavutil/avstring.h"
#include "libavutil/opt.h"
#include "internal.h"
#include "url.h"
// encourage reads of 4096 bytes - 1 block is always retained.
#define MAX_BUFFER_BLOCKS 257
#define BLOCKSIZE 16
typedef struct CryptoContext {
const AVClass *class;
URLContext *hd;
uint8_t inbuffer [BLOCKSIZE*MAX_BUFFER_BLOCKS],
outbuffer[BLOCKSIZE*MAX_BUFFER_BLOCKS];
uint8_t *outptr;
int indata, indata_used, outdata;
int64_t position; // position in file - used in seek
int flags;
int eof;
uint8_t *key;
int keylen;
uint8_t *iv;
int ivlen;
uint8_t *decrypt_key;
int decrypt_keylen;
uint8_t *decrypt_iv;
int decrypt_ivlen;
uint8_t *encrypt_key;
int encrypt_keylen;
uint8_t *encrypt_iv;
int encrypt_ivlen;
struct AVAES *aes_decrypt;
struct AVAES *aes_encrypt;
uint8_t pad[BLOCKSIZE];
int pad_len;
} CryptoContext;
#define OFFSET(x) offsetof(CryptoContext, x)
#define D AV_OPT_FLAG_DECODING_PARAM
#define E AV_OPT_FLAG_ENCODING_PARAM
static const AVOption options[] = {
{"key", "AES encryption/decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, .flags = D|E },
{"iv", "AES encryption/decryption initialization vector", OFFSET(iv), AV_OPT_TYPE_BINARY, .flags = D|E },
{"decryption_key", "AES decryption key", OFFSET(decrypt_key), AV_OPT_TYPE_BINARY, .flags = D },
{"decryption_iv", "AES decryption initialization vector", OFFSET(decrypt_iv), AV_OPT_TYPE_BINARY, .flags = D },
{"encryption_key", "AES encryption key", OFFSET(encrypt_key), AV_OPT_TYPE_BINARY, .flags = E },
{"encryption_iv", "AES encryption initialization vector", OFFSET(encrypt_iv), AV_OPT_TYPE_BINARY, .flags = E },
{ NULL }
};
static const AVClass crypto_class = {
.class_name = "crypto",
.item_name = av_default_item_name,
.option = options,
.version = LIBAVUTIL_VERSION_INT,
};
static int set_aes_arg(CryptoContext *c, uint8_t **buf, int *buf_len,
uint8_t *default_buf, int default_buf_len,
const char *desc)
{
if (!*buf_len) {
if (!default_buf_len) {
av_log(c, AV_LOG_ERROR, "%s not set\n", desc);
return AVERROR(EINVAL);
} else if (default_buf_len != BLOCKSIZE) {
av_log(c, AV_LOG_ERROR,
"invalid %s size (%d bytes, block size is %d)\n",
desc, default_buf_len, BLOCKSIZE);
return AVERROR(EINVAL);
}
*buf = av_memdup(default_buf, default_buf_len);
if (!*buf)
return AVERROR(ENOMEM);
*buf_len = default_buf_len;
} else if (*buf_len != BLOCKSIZE) {
av_log(c, AV_LOG_ERROR,
"invalid %s size (%d bytes, block size is %d)\n",
desc, *buf_len, BLOCKSIZE);
return AVERROR(EINVAL);
}
return 0;
}
static int crypto_open2(URLContext *h, const char *uri, int flags, AVDictionary **options)
{
const char *nested_url;
int ret = 0;
CryptoContext *c = h->priv_data;
c->flags = flags;
if (!av_strstart(uri, "crypto+", &nested_url) &&
!av_strstart(uri, "crypto:", &nested_url)) {
av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
ret = AVERROR(EINVAL);
goto err;
}
c->position = 0;
if (flags & AVIO_FLAG_READ) {
if ((ret = set_aes_arg(c, &c->decrypt_key, &c->decrypt_keylen,
c->key, c->keylen, "decryption key")) < 0)
goto err;
if ((ret = set_aes_arg(c, &c->decrypt_iv, &c->decrypt_ivlen,
c->iv, c->ivlen, "decryption IV")) < 0)
goto err;
}
if (flags & AVIO_FLAG_WRITE) {
if ((ret = set_aes_arg(c, &c->encrypt_key, &c->encrypt_keylen,
c->key, c->keylen, "encryption key")) < 0)
if (ret < 0)
goto err;
if ((ret = set_aes_arg(c, &c->encrypt_iv, &c->encrypt_ivlen,
c->iv, c->ivlen, "encryption IV")) < 0)
goto err;
}
if ((ret = ffurl_open_whitelist(&c->hd, nested_url, flags,
&h->interrupt_callback, options,
h->protocol_whitelist, h->protocol_blacklist, h)) < 0) {
av_log(h, AV_LOG_ERROR, "Unable to open resource: %s\n", nested_url);
goto err;
}
if (flags & AVIO_FLAG_READ) {
c->aes_decrypt = av_aes_alloc();
if (!c->aes_decrypt) {
ret = AVERROR(ENOMEM);
goto err;
}
ret = av_aes_init(c->aes_decrypt, c->decrypt_key, BLOCKSIZE*8, 1);
if (ret < 0)
goto err;
// pass back information about the context we openned
if (c->hd->is_streamed)
h->is_streamed = c->hd->is_streamed;
}
if (flags & AVIO_FLAG_WRITE) {
c->aes_encrypt = av_aes_alloc();
if (!c->aes_encrypt) {
ret = AVERROR(ENOMEM);
goto err;
}
ret = av_aes_init(c->aes_encrypt, c->encrypt_key, BLOCKSIZE*8, 0);
if (ret < 0)
goto err;
// for write, we must be streamed
// - linear write only for crytpo aes-128-cbc
h->is_streamed = 1;
}
c->pad_len = 0;
err:
return ret;
}
static int crypto_read(URLContext *h, uint8_t *buf, int size)
{
CryptoContext *c = h->priv_data;
int blocks;
retry:
if (c->outdata > 0) {
size = FFMIN(size, c->outdata);
memcpy(buf, c->outptr, size);
c->outptr += size;
c->outdata -= size;
c->position = c->position + size;
return size;
}
// We avoid using the last block until we've found EOF,
// since we'll remove PKCS7 padding at the end. So make
// sure we've got at least 2 blocks, so we can decrypt
// at least one.
while (c->indata - c->indata_used < 2*BLOCKSIZE) {
int n = ffurl_read(c->hd, c->inbuffer + c->indata,
sizeof(c->inbuffer) - c->indata);
if (n <= 0) {
c->eof = 1;
break;
}
c->indata += n;
}
blocks = (c->indata - c->indata_used) / BLOCKSIZE;
if (!blocks)
return AVERROR_EOF;
if (!c->eof)
blocks--;
av_aes_crypt(c->aes_decrypt, c->outbuffer, c->inbuffer + c->indata_used,
blocks, c->decrypt_iv, 1);
c->outdata = BLOCKSIZE * blocks;
c->outptr = c->outbuffer;
c->indata_used += BLOCKSIZE * blocks;
if (c->indata_used >= sizeof(c->inbuffer)/2) {
memmove(c->inbuffer, c->inbuffer + c->indata_used,
c->indata - c->indata_used);
c->indata -= c->indata_used;
c->indata_used = 0;
}
if (c->eof) {
// Remove PKCS7 padding at the end
int padding = c->outbuffer[c->outdata - 1];
c->outdata -= padding;
}
goto retry;
}
static int64_t crypto_seek(URLContext *h, int64_t pos, int whence)
{
CryptoContext *c = h->priv_data;
int64_t block;
int64_t newpos;
if (c->flags & AVIO_FLAG_WRITE) {
av_log(h, AV_LOG_ERROR,
"Crypto: seek not supported for write\r\n");
/* seems the most appropriate error to return */
return AVERROR(ESPIPE);
}
// reset eof, else we won't read it correctly if we already hit eof.
c->eof = 0;
switch (whence) {
case SEEK_SET:
break;
case SEEK_CUR:
pos = pos + c->position;
break;
case SEEK_END: {
int64_t newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
if (newpos < 0) {
av_log(h, AV_LOG_ERROR,
"Crypto: seek_end - can't get file size (pos=%lld)\r\n", (long long int)pos);
return newpos;
}
pos = newpos - pos;
}
break;
case AVSEEK_SIZE: {
int64_t newpos = ffurl_seek( c->hd, pos, AVSEEK_SIZE );
return newpos;
}
break;
default:
av_log(h, AV_LOG_ERROR,
"Crypto: no support for seek where 'whence' is %d\r\n", whence);
return AVERROR(EINVAL);
}
c->outdata = 0;
c->indata = 0;
c->indata_used = 0;
c->outptr = c->outbuffer;
// identify the block containing the IV for the
// next block we will decrypt
block = pos/BLOCKSIZE;
if (block == 0) {
// restore the iv to the seed one - this is the iv for the FIRST block
memcpy( c->decrypt_iv, c->iv, c->ivlen );
c->position = 0;
} else {
// else, go back one block - we will get av_cyrpt to read this block
// which it will then store use as the iv.
// note that the DECRYPTED result will not be correct,
// but will be discarded
block--;
c->position = (block * BLOCKSIZE);
}
newpos = ffurl_seek( c->hd, c->position, SEEK_SET );
if (newpos < 0) {
av_log(h, AV_LOG_ERROR,
"Crypto: nested protocol no support for seek or seek failed\n");
return newpos;
}
// read and discard from here up to required position
// (which will set the iv correctly to it).
if (pos - c->position) {
uint8_t buff[BLOCKSIZE*2]; // maximum size of pos-c->position
int len = pos - c->position;
int res;
while (len > 0) {
// note: this may not return all the bytes first time
res = crypto_read(h, buff, len);
if (res < 0)
break;
len -= res;
}
// if we did not get all the bytes
if (len != 0) {
char errbuf[100] = "unknown error";
av_strerror(res, errbuf, sizeof(errbuf));
av_log(h, AV_LOG_ERROR,
"Crypto: discard read did not get all the bytes (%d remain) - read returned (%d)-%s\n",
len, res, errbuf);
return AVERROR(EINVAL);
}
}
return c->position;
}
static int crypto_write(URLContext *h, const unsigned char *buf, int size)
{
CryptoContext *c = h->priv_data;
int total_size, blocks, pad_len, out_size;
uint8_t *out_buf;
int ret = 0;
total_size = size + c->pad_len;
pad_len = total_size % BLOCKSIZE;
out_size = total_size - pad_len;
blocks = out_size / BLOCKSIZE;
if (out_size) {
out_buf = av_malloc(out_size);
if (!out_buf)
return AVERROR(ENOMEM);
if (c->pad_len) {
memcpy(&c->pad[c->pad_len], buf, BLOCKSIZE - c->pad_len);
av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);
blocks--;
}
av_aes_crypt(c->aes_encrypt, &out_buf[c->pad_len ? BLOCKSIZE : 0],
&buf[c->pad_len ? BLOCKSIZE - c->pad_len: 0],
blocks, c->encrypt_iv, 0);
ret = ffurl_write(c->hd, out_buf, out_size);
av_free(out_buf);
if (ret < 0)
return ret;
memcpy(c->pad, &buf[size - pad_len], pad_len);
} else
memcpy(&c->pad[c->pad_len], buf, size);
c->pad_len = pad_len;
return size;
}
static int crypto_close(URLContext *h)
{
CryptoContext *c = h->priv_data;
uint8_t out_buf[BLOCKSIZE];
int ret, pad;
if (c->aes_encrypt) {
pad = BLOCKSIZE - c->pad_len;
memset(&c->pad[c->pad_len], pad, pad);
av_aes_crypt(c->aes_encrypt, out_buf, c->pad, 1, c->encrypt_iv, 0);
if ((ret = ffurl_write(c->hd, out_buf, BLOCKSIZE)) < 0)
return ret;
}
if (c->hd)
ffurl_close(c->hd);
av_freep(&c->aes_decrypt);
av_freep(&c->aes_encrypt);
return 0;
}
const URLProtocol ff_crypto_protocol = {
.name = "crypto",
.url_open2 = crypto_open2,
.url_seek = crypto_seek,
.url_read = crypto_read,
.url_write = crypto_write,
.url_close = crypto_close,
.priv_data_size = sizeof(CryptoContext),
.priv_data_class = &crypto_class,
.flags = URL_PROTOCOL_FLAG_NESTED_SCHEME,
};
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