PeerStreamer

/*

 * Decryption protocol handler

 * Copyright (c) 2011 Martin Storsjo

 *

 * This file is part of Libav.

 *

 * Libav 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.

 *

 * Libav 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 Libav; 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"

#define MAX_BUFFER_BLOCKS 150

#define BLOCKSIZE 16

typedef struct {

    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;

    int eof;

    uint8_t *key;

    int keylen;

    uint8_t *iv;

    int ivlen;

    struct AVAES *aes;

} CryptoContext;

#define OFFSET(x) offsetof(CryptoContext, x)

static const AVOption options[] = {

    {"key", "AES decryption key", OFFSET(key), FF_OPT_TYPE_BINARY },

    {"iv",  "AES decryption initialization vector", OFFSET(iv),  FF_OPT_TYPE_BINARY },

    { NULL }

};

static const AVClass crypto_class = {

    "crypto", av_default_item_name, options, LIBAVUTIL_VERSION_INT

};

static int crypto_open(URLContext *h, const char *uri, int flags)

{

    const char *nested_url;

    int ret;

    CryptoContext *c = h->priv_data;

    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;

    }

    if (c->keylen < BLOCKSIZE || c->ivlen < BLOCKSIZE) {

        av_log(h, AV_LOG_ERROR, "Key or IV not set\n");

        ret = AVERROR(EINVAL);

        goto err;

    }

    if (flags & AVIO_FLAG_WRITE) {

        av_log(h, AV_LOG_ERROR, "Only decryption is supported currently\n");

        ret = AVERROR(ENOSYS);

        goto err;

    }

    if ((ret = ffurl_open(&c->hd, nested_url, AVIO_FLAG_READ)) < 0) {

        av_log(h, AV_LOG_ERROR, "Unable to open input\n");

        goto err;

    }

    c->aes = av_mallocz(av_aes_size);

    if (!c->aes) {

        ret = AVERROR(ENOMEM);

        goto err;

    }

    av_aes_init(c->aes, c->key, 128, 1);

    h->is_streamed = 1;

    return 0;

err:

    av_free(c->key);

    av_free(c->iv);

    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;

        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, c->outbuffer, c->inbuffer + c->indata_used, blocks,

                 c->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 int crypto_close(URLContext *h)

{

    CryptoContext *c = h->priv_data;

    if (c->hd)

        ffurl_close(c->hd);

    av_freep(&c->aes);

    av_freep(&c->key);

    av_freep(&c->iv);

    return 0;

}

URLProtocol ff_crypto_protocol = {

    .name            = "crypto",

    .url_open        = crypto_open,

    .url_read        = crypto_read,

    .url_close       = crypto_close,

    .priv_data_size  = sizeof(CryptoContext),

    .priv_data_class = &crypto_class,

    .flags           = URL_PROTOCOL_FLAG_NESTED_SCHEME,

};