[erlang-questions] Crypto AES data block size

[John Kemp]

On 06/20/2014 07:00 AM, Alexander Petrovsky wrote:
> Hi!
>
> I need to encrypt some data with ads_cbc_128, and I do like:
>
> crypto:aes_cbc_128_encrypt(<<"B3E80545C3C9968096E85A7E0A4A5779">>,
> <<"96E85A7E0A4A5779">>,
> <<"id=14&bid=00.004300&clickUrl=http://duckduckgo.com&pid=3101&source=100&search-id=42&search-date=00:00:00">>).
> ** exception error: bad argument
>       in function  crypto:aes_cbc_crypt/4
>          called as
> crypto:aes_cbc_crypt(<<"B3E80545C3C9968096E85A7E0A4A5779">>,
>                                         <<"96E85A7E0A4A5779">>,
>
>   <<"id=14&bid=00.004300&clickUrl=http://duckduckgo.com&pid=3101&source=100&search-id=42&search-date=00:00:00">>,
>                                         true)
>
> seems like the size of data should be the equal the power on 2, and then
> I do:
>
> crypto:aes_cbc_128_encrypt(<<"B3E80545C3C9968096E85A7E0A4A5779">>,
> <<"96E85A7E0A4A5779">>,
> <<"id=14&bid=00.004300&clickUrl=http://duckduckgo.com&pid=3101&source=100&search-id=42&search-date=00:00:00",
> 0:24/unit:8>>).
> <<87,187,244,217,66,251,202,118,238,90,226,245,209,213,
>    158,166,203,46,8,30,113,122,172,204,163,50,193,34,243,
>    ...>>
>
> Is there any way, don't fill the binary by zeros?

The crypto:aes_cbc_128_encrypt API requires data be padded to a multiple 
of 16 bytes (as it says in the documentation - for example: 
http://www.erlang.org/documentation/doc-5.8.3/lib/crypto-2.0.2.1/doc/html/crypto.html#aes_cbc_128_encrypt-3).

  How properly I should
> do this?

https://github.com/spawngrid/cowboy_session/blob/master/src/cowboy_session_secure.erl 
shows what looks like a good example of how to do the padding more 
generally than in your example.

- johnk
>
>
> --
> Петровский Александр / Alexander Petrovsky,
>
> Skype: askjuise
> Phone: +7 914 8 820 815
>
>
>
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