[OTR-dev] How to properly detect the end of the AKE?

[Thomas Balthazar]

On 30 Oct 2013, at 18:46, Ian Goldberg <ian at cypherpunks.ca> wrote:

> On Wed, Oct 30, 2013 at 03:44:47PM +0100, Thomas Balthazar wrote:
>> Hi,
>> 
>> * The situation :
>> I use libotr v4.0.0 in an iOS app I'm working on.
>> The objective-c wrapper I use is here :
>> https://github.com/tbalthazar/TBOTRManager
>> 
>> * My goal :
>> I try to have my app exchange messages with another app that uses OTR too (but not libotr).
>> When the user wants to send an OTR message with my app, I keep this message until the OTR conversation is secured.
>> I'd like to know *when* I can consider the OTR conversation as secured and send the very first user message.
>> 
>> * My problem
>> I tried to consider the gone_secure callback as the signal that the conversation was secure, but it seems that the gone_secure callback is called before libotr has sent the signature message (?OTR:AAMS), which seem to trigger an error on the recipient side.
>> 
>> This is the sequence I observe :
>> 
>> - user wants to send "hello", I don't send his message yet and :
>> - I send ?OTRv23?
>> - I receive ?OTR:AAMC
>> - I send ?OTR:AAMK
>> - I receive ?OTR:AAMR
>> - gone_secure callback is called
>> - I send ?OTR:AAMD (the "hello" user message)
>> - I send ?OTR:AAMS
>> - I receive ?OTR Error
>> 
>> The recipient client refuses my "hello" message since it considers the conversation is not secure yet. If I delay the sending of the "hello" message for a few seconds, everything works fine.
>> 
>> Is there a callback I can plug in or a value I can observe to help me determine when I can send the user "hello" message? 
>> 
>> Please let me know if I miss something obvious.
>> 
>> Thanks a lot for your help!
>> Thomas.
> 
> Ah, interesting problem.  libotr indeed calls the gone_secure callback
> when the conversation switches to encrypted at your end.  But right
> after that (i.e. when otrl_message_receiving returns), it returns to you
> the AAMS message, which your application then delivers to the other side.
> 
> So I guess you could have gone_secure just set a flag, which you check
> (and clear) after you deliver that AAMS message?
> 
>   - Ian

Thanks for your answer, Ian.
I was wondering if there was a specific callback or method to detect the AAMS message "elegantly" but I guess I'll just test if the string starts with "?OTR:AAMS" then.

Thanks again,
Thomas.