1. ffmpeg
  2. Commit b3e144a7dfc6953df3b3e478eb8b8521ab5c6ecc
Browse code

des: add possibility to calculate DES-CBC-MAC with small buffer

This patch adds the possibility to calculate the DES-CBC-MAC of a
source buffer (i.e. the last block of the buffer encrypted in CBC
mode) without having to allocate a destination buffer that is as
long as the complete source buffer, but instead only 8 bytes
for the MAC.

Signed-off-by: David Goldwich <david.goldwich@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

David Goldwich authored on 2011/09/02 15:20:58
Showing 2 changed files
libavutil/des.c
History View file @ b3e144a
... ... 
@@ -298,7 +298,7 @@ int av_des_init(AVDES *d, const uint8_t *key, int key_bits, int decrypt) {
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     return 0;
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 }
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-void av_des_crypt(AVDES *d, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {
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+static void av_des_crypt_mac(AVDES *d, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt, int mac) {
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     uint64_t iv_val = iv ? AV_RB64(iv) : 0;
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     while (count-- > 0) {
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         uint64_t dst_val;
... ... 
@@ -321,12 +321,21 @@ void av_des_crypt(AVDES *d, uint8_t *dst, const uint8_t *src, int count, uint8_t
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         }
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         AV_WB64(dst, dst_val);
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         src += 8;
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-        dst += 8;
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+        if (!mac)
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+            dst += 8;
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     }
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     if (iv)
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         AV_WB64(iv, iv_val);
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 }
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+void av_des_crypt(AVDES *d, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {
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+    av_des_crypt_mac(d, dst, src, count, iv, decrypt, 0);
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+}
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+
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+void av_des_mac(AVDES *d, uint8_t *dst, const uint8_t *src, int count) {
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+    av_des_crypt_mac(d, dst, src, count, (uint8_t[8]){0}, 0, 1);
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+}
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+
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 #ifdef TEST
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 #undef printf
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 #undef rand
libavutil/des.h
History View file @ b3e144a
... ... 
@@ -33,7 +33,7 @@ struct AVDES {
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  * @brief Initializes an AVDES context.
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  *
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  * @param key_bits must be 64 or 192
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- * @param decrypt 0 for encryption, 1 for decryption
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+ * @param decrypt 0 for encryption/CBC-MAC, 1 for decryption
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  */
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 int av_des_init(struct AVDES *d, const uint8_t *key, int key_bits, int decrypt);
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... ... 
@@ -49,4 +49,13 @@ int av_des_init(struct AVDES *d, const uint8_t *key, int key_bits, int decrypt);
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  */
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 void av_des_crypt(struct AVDES *d, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt);
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+/**
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+ * @brief Calculates CBC-MAC using the DES algorithm.
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+ *
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+ * @param count number of 8 byte blocks
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+ * @param dst destination array, can be equal to src, must be 8-byte aligned
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+ * @param src source array, can be equal to dst, must be 8-byte aligned, may be NULL
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+ */
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+void av_des_mac(struct AVDES *d, uint8_t *dst, const uint8_t *src, int count);
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+
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 #endif /* AVUTIL_DES_H */