FFmpeg: libavformat/crypto.c Source File

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libavformat

crypto.c

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1 /*

2 * Decryption protocol handler

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 */

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"

29 #define MAX_BUFFER_BLOCKS 150

30 #define BLOCKSIZE 16

32 typedef 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;

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

48 #define D AV_OPT_FLAG_DECODING_PARAM

49 static 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 };

55 static const AVClass crypto_class = {

56 .class_name = "crypto",

57 .item_name = av_default_item_name,

58 .option = options,

59 .version = LIBAVUTIL_VERSION_INT,

60 };

62 static int crypto_open2(URLContext *h, const char *uri, int flags, AVDictionary **options)

63 {

64 const char *nested_url;

65 int ret = 0;

66 CryptoContext *c = h->priv_data;

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 }

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, options)) < 0) {

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

88 goto err;

89 }

90 c->aes = av_aes_alloc();

91 if (!c->aes) {

92 ret = AVERROR(ENOMEM);

93 goto err;

94 }

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

98 h->is_streamed = 1;

100 err:

101 return ret;

102 }

103

104 static int crypto_read(URLContext *h, uint8_t *buf, int size)

105 {

106 CryptoContext *c = h->priv_data;

107 int blocks;

108 retry:

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

153 static 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

162 URLProtocol ff_crypto_protocol = {

163 .name = "crypto",

164 .url_open2 = crypto_open2,

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 };

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