[erlang-questions] How to use crypto:hmac_init() and friends?
Thu Nov 19 15:27:48 CET 2015
Wouldn't it make sense to introduce a separate data type for these custom data? Or even allow to define new custom types in nifs or drivers with serialization and comparison rules.
On 20 November 2015 1:18:42 AM AEDT, Sverker Eriksson <sverker.eriksson@REDACTED> wrote:
>On 11/19/2015 02:37 PM, Frans Schneider wrote:
>> Dear list,
>> I have to create the HMAC of a message by including data at several
>> points in my code as shown below:
>> Mac_ctxt_init = crypto:hmac_init(sha256, Mac_key),
>> Mac_ctxt = case Version of
>> 3 ->
>> Mac_ctxt1 = crypto:hmac_update(Mac_ctxt_init,
>> crypto:hmac_update(Mac_ctxt1, Dhir_pub);
>> 2 ->
>> LMac_ctxt = crypto:hmac_update(Mac_ctxt, <<Version/binary,
>> LMac = crypto:hmac_final_n(LMac_ctxt, 8),
>> This will always return <<>>! It already starts with the hmac_init()
>> which returns <<>>.
>> Erlang/OTP 18 [erts-7.1] [source] [64-bit] [smp:2:2]
>> [async-threads:10] [hipe] [kernel-poll:false]
>> Eshell V7.1 (abort with ^G)
>> 1> K =
>> 2> crypto:hmac_init(sha256, K).
>> Using crypto:hmac(sha256, K, Data, 8) works fine, but is not usable.
>> Any idea what goes wrong or what I am doing wrong?
>Nothing is wrong (ugly maybe, but not wrong).
>That empty binary is not really empty. It's a magic binary!
>It's referring some internal emulator state (the hmac context in this
>Just pass it along to hmac_update and hmac_final and you will get a
>regular binary in the end.
>The magic binary looks and behaves like an empty binary. It will even
>lose its magic powers
>and turn into a regular binary if serialized with term_to_binary.
>erlang-questions mailing list
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