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ffmpeg / libavformat / crypto.c @ 4a7a1b7d

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/*
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 * Decryption protocol handler
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 * Copyright (c) 2011 Martin Storsjo
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "avformat.h"
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#include "libavutil/aes.h"
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#include "libavutil/avstring.h"
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#include "libavutil/opt.h"
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#include "internal.h"
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#include "url.h"
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#define MAX_BUFFER_BLOCKS 150
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#define BLOCKSIZE 16
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typedef struct {
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    const AVClass *class;
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    URLContext *hd;
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    uint8_t inbuffer [BLOCKSIZE*MAX_BUFFER_BLOCKS],
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            outbuffer[BLOCKSIZE*MAX_BUFFER_BLOCKS];
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    uint8_t *outptr;
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    int indata, indata_used, outdata;
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    int eof;
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    uint8_t *key;
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    int keylen;
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    uint8_t *iv;
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    int ivlen;
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    struct AVAES *aes;
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} CryptoContext;
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#define OFFSET(x) offsetof(CryptoContext, x)
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static const AVOption options[] = {
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    {"key", "AES decryption key", OFFSET(key), FF_OPT_TYPE_BINARY },
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    {"iv",  "AES decryption initialization vector", OFFSET(iv),  FF_OPT_TYPE_BINARY },
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    { NULL }
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};
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static const AVClass crypto_class = {
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    .class_name     = "crypto",
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    .item_name      = av_default_item_name,
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    .option         = options,
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    .version        = LIBAVUTIL_VERSION_INT,
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};
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static int crypto_open(URLContext *h, const char *uri, int flags)
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{
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    const char *nested_url;
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    int ret;
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    CryptoContext *c = h->priv_data;
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    if (!av_strstart(uri, "crypto+", &nested_url) &&
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        !av_strstart(uri, "crypto:", &nested_url)) {
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        av_log(h, AV_LOG_ERROR, "Unsupported url %s\n", uri);
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        ret = AVERROR(EINVAL);
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        goto err;
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    }
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    if (c->keylen < BLOCKSIZE || c->ivlen < BLOCKSIZE) {
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        av_log(h, AV_LOG_ERROR, "Key or IV not set\n");
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        ret = AVERROR(EINVAL);
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        goto err;
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    }
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    if (flags & AVIO_FLAG_WRITE) {
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        av_log(h, AV_LOG_ERROR, "Only decryption is supported currently\n");
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        ret = AVERROR(ENOSYS);
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        goto err;
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    }
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    if ((ret = ffurl_open(&c->hd, nested_url, AVIO_FLAG_READ)) < 0) {
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        av_log(h, AV_LOG_ERROR, "Unable to open input\n");
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        goto err;
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    }
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    c->aes = av_mallocz(av_aes_size);
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    if (!c->aes) {
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        ret = AVERROR(ENOMEM);
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        goto err;
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    }
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    av_aes_init(c->aes, c->key, 128, 1);
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    h->is_streamed = 1;
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    return 0;
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err:
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    av_free(c->key);
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    av_free(c->iv);
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    return ret;
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}
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static int crypto_read(URLContext *h, uint8_t *buf, int size)
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{
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    CryptoContext *c = h->priv_data;
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    int blocks;
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retry:
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    if (c->outdata > 0) {
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        size = FFMIN(size, c->outdata);
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        memcpy(buf, c->outptr, size);
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        c->outptr  += size;
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        c->outdata -= size;
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        return size;
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    }
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    // We avoid using the last block until we've found EOF,
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    // since we'll remove PKCS7 padding at the end. So make
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    // sure we've got at least 2 blocks, so we can decrypt
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    // at least one.
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    while (c->indata - c->indata_used < 2*BLOCKSIZE) {
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        int n = ffurl_read(c->hd, c->inbuffer + c->indata,
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                           sizeof(c->inbuffer) - c->indata);
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        if (n <= 0) {
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            c->eof = 1;
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            break;
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        }
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        c->indata += n;
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    }
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    blocks = (c->indata - c->indata_used) / BLOCKSIZE;
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    if (!blocks)
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        return AVERROR_EOF;
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    if (!c->eof)
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        blocks--;
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    av_aes_crypt(c->aes, c->outbuffer, c->inbuffer + c->indata_used, blocks,
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                 c->iv, 1);
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    c->outdata      = BLOCKSIZE * blocks;
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    c->outptr       = c->outbuffer;
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    c->indata_used += BLOCKSIZE * blocks;
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    if (c->indata_used >= sizeof(c->inbuffer)/2) {
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        memmove(c->inbuffer, c->inbuffer + c->indata_used,
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                c->indata - c->indata_used);
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        c->indata     -= c->indata_used;
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        c->indata_used = 0;
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    }
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    if (c->eof) {
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        // Remove PKCS7 padding at the end
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        int padding = c->outbuffer[c->outdata - 1];
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        c->outdata -= padding;
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    }
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    goto retry;
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}
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static int crypto_close(URLContext *h)
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{
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    CryptoContext *c = h->priv_data;
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    if (c->hd)
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        ffurl_close(c->hd);
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    av_freep(&c->aes);
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    av_freep(&c->key);
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    av_freep(&c->iv);
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    return 0;
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}
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URLProtocol ff_crypto_protocol = {
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    .name            = "crypto",
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    .url_open        = crypto_open,
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    .url_read        = crypto_read,
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    .url_close       = crypto_close,
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    .priv_data_size  = sizeof(CryptoContext),
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    .priv_data_class = &crypto_class,
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    .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,
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};