[OTR-users] otr modify toolkit

[Ian Goldberg]

On Thu, May 21, 2015 at 07:36:04PM +0200, Bjorn Kuiper wrote:
> Hi,
> 
>  
> 
> I'm having some problems using the otr_modify application from the otrlib
> toolkit.
> 
>  
> 
> Could somebody explain to me where I can get the mackey that is needed as
> the first parameter?
> 
>  
> 
> Assume I send the following text
> 
>  
> 
> "hi bob, my name is alice"
> 
>  
> 
> Which is encrypted into the following data message:
> 
> ?OTR:AAMD8E6ZSifXvlYAAAAAAQAAAAEAAADAD2DA/+dQWOE0SbzhRlF9MNezfZxG+qNXzGaJ65W
> j3qr/72f1MSx1lSxJ2hZ0HX22rFbO3ctAY97iMNwVoZGW7WRj4Fy3JZWZ8ATxLOSzX26DF9Ft/O1
> h8Ndu5gzVYoUsXAj0Q+UCkMD9jR2Pv6/ykLhx1eHyznpIFDxkExblcdOcFAHZX8iWeIocuCrsF8A
> oRMPTHsB3x8XXergQ6XOzOUQTNjyBSdoV46CFk3qWGJy8OC3HQPQhG4voP1wyvBUJAAAAAAAAAAE
> AAAAZoCjmoJICwz+7CJZ//uMLWbrm9pT4ABiURY39QOGdMud4QQIA3gI1pXh+KUIWAAAAAA==.
> 
>  
> 
> Wouldn't the mackey be the key that I can retrieve using otr_parse, thus:
> 8dfd40e19d32e778410200de0235a5787e294216 ?

No, that's the MAC tag, not the MAC key.

> Or would it be the mackey that I would retrieve when re-establishing a new
> DH key and get it from the list of old mackeys?

Indeed.  There are two ways to get the MAC key.  One is if you know the
private part of a DH key, in which case you can use otr_sesskeys to get
it.  The other is if you have a transcripts containing later messages
that contain this key as an "old mackey", which you get with otr_parse.

   - Ian