[Pidgin] #4380: Add Triple-DES cipher to libpurple

[Pidgin]

#4380: Add Triple-DES cipher to libpurple
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 Reporter:  QuLogic                   |       Type:  patch
   Status:  new                       |   Priority:  minor
Component:  libpurple                 |    Version:  2.3.1
 Keywords:  triple-des, des3, cipher  |    Pending:  0    
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 So khc wanted to take a look at the MSNP15 stuff, so I'm posting these
 tickets.

 This patch adds the Triple-DES cipher to libpurple. It is available as
 "des3". You can only use EDE3 mode with 3 keys and not anything else
 because that's all I needed. It can be run in ECB or CBC batch mode by
 using `purple_cipher_context_set_option(cipher, "batchMode",
 PurpleCipherBatchMode mode)`.

 Finally, there are a few tests from NIST added to test_cipher.c. They
 check both encrypting and decrypting, so I've added decryption to the DES
 cipher as well.

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Ticket URL: <http://developer.pidgin.im/ticket/4380>
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