[OTR-users] otr modify toolkit

[Bjorn Kuiper]

> -----Oorspronkelijk bericht-----
> Van: otr-users-bounces at lists.cypherpunks.ca [mailto:otr-users-
> bounces at lists.cypherpunks.ca] Namens Bjorn Kuiper
> Verzonden: Tuesday, June 30, 2015 2:04 AM
> Aan: otr-users at lists.cypherpunks.ca
> CC: ian at cypherpunks.ca
> Onderwerp: Re: [OTR-users] otr modify toolkit
> 
> > 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/+dQWOE0SbzhRlF9M
> > NezfZxG+qNXz
> > > GaJ65W
> > >
> >
> j3qr/72f1MSx1lSxJ2hZ0HX22rFbO3ctAY97iMNwVoZGW7WRj4Fy3JZWZ8ATxL
> > OSzX26DF
> > > 9Ft/O1
> > >
> >
> h8Ndu5gzVYoUsXAj0Q+UCkMD9jR2Pv6/ykLhx1eHyznpIFDxkExblcdOcFAHZX
> > 8iWeIocu
> > > h8Ndu5gzVYoUsXAj0Q+CrsF8A
> > >
> >
> oRMPTHsB3x8XXergQ6XOzOUQTNjyBSdoV46CFk3qWGJy8OC3HQPQhG4voP
> > 1wyvBUJAAAAA
> > > AAAAAE
> > >
> >
> AAAAZoCjmoJICwz+7CJZ//uMLWbrm9pT4ABiURY39QOGdMud4QQIA3gI1pX
> > h+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
> 
> So consider the attached private key pidgin file, the private key of __bob
> would be "2E3342837ACFB215EF502845CB48BB724762B950" whereas the
> public key of __alice would be
> "009D1F02172287D532DA187202FD752EB372AB8A16130927E9BE1B214538535
> 44872E0126F0
> 8CB9F5BCB5345E5B83E62058663AD511CA601A59EEA73C8904C4B25915B3B8C
> 3CE39CF108E1E
> 11F7AA4C258112554CD5A325C3A8613F9365586AAA0904B0FEBEFB6F643B920
> 9D79180EEF319
> D5A75EEE800D39C44A26CA672C38567".
> 
> Running this through otr_sesskeys results in
> --
> We are the high end of this key exchange.
> 
> Our public key:
> c44ea24c97b2e231d3846f25d7336512f3492869fbd30a9a0051fe9abfcffb0e512
> bff9df3cc
> 88ae3c2d3291d5993957a254b422e0bea47897bbf0e37bd02d58c4baf891f99197
> a611d47891
> ba827930a1dbce7fb4b591c833c71913f9489554ebb29a1f4b5b5b7bbbc86c08f5
> 995af4ab90
> 854a0d422935ceed4cf35eb6c366464a224b6522ae1b450f09c92a3a874f19c05a9
> e6a755ee0
> 7f432119d5555db10651a926f2dd595d2fc60ccfe30ec0b5ac3d730b22c2af8fd662
> 510ebf87
> 6d0a
> 
> Session id: b3c7046430ea2e0c1e29bb1b74bab8c7c5e82608
> 
> Sending   AES key: 38433fc99476c6dec00905700876740b
> Sending   MAC key: bb307c86b269201b33e8f4606f8f541d8a11c3bd
> Receiving AES key: a3d04c132c68a9697d1092225304d097 Receiving MAC key:
> d4def44ed4178c84a693a14516d344b7917b23a2
> --
> 
> Where our focus is on the receiving MAC key.
> 
> We use this MAC key to modify our message that we send to __alice, saying
> "hoi alice":
> ?OTR:AAMDJ9e+VvBOmUoAAAAAAQAAAAEAAADA/QzMtslPdMiwOhStWZ
> G5HQ7h9tdpb9KpM7R57Gv
> MHHGDbFH1VDc74L3OHJdRprso5ZLsaQK9Rx3s7ZFIh6ubbDvsm/HPUCoZGwe
> 1fadGV7d/v9+Eyg/
> 0jnjh0lGVDIT+W6d5Ia0EmHIzS9G6hsAugpK9Pk370JTL0bSaJIyzWYeZamSo4+O
> wJcusmiK
> 0jnjh0lGVDIT+W6d5Ia0EmHIzS9G6hsAugpK9Pk370JTL0bSaJIyzWYeZamSo4+rf
> WC
> 15KiqGKWn0v29UYCpjrrgIlTj96Wmgo0yCFg+IEbCpssK0uSRa33kyqQTnpLthBjq
> AAAAAAA
> 15KiqGKWn0v29UYCpjrrgIlTj96Wmgo0yCFg+AAAE
> AAAAKSrXNbc4fKYnZctVOW6P8z1koqGmSqMqRM+1o18P3AAAAAA==.
> 
> Thus running otr_modify as follows
> --
> $ ./otr_modify.exe d4def44ed4178c84a693a14516d344b7917b23a2 alice bjorn
> 4
> ?OTR:AAMDJ9e+VvBOmUoAAAAAAQAAAAEAAADA/QzMtslPdMiwOhStWZ
> G5HQ7h9tdpb9KpM7R57Gv
> MHHGDbFH1VDc74L3OHJdRprso5ZLsaQK9Rx3s7ZFIh6ubbDvsm/HPUCoZGwe
> 1fadGV7d/v9+Eyg/
> 0jnjh0lGVDIT+W6d5Ia0EmHIzS9G6hsAugpK9Pk370JTL0bSaJIyzWYeZamSo4+O
> wJcusmiK
> 0jnjh0lGVDIT+W6d5Ia0EmHIzS9G6hsAugpK9Pk370JTL0bSaJIyzWYeZamSo4+rf
> WC
> 15KiqGKWn0v29UYCpjrrgIlTj96Wmgo0yCFg+IEbCpssK0uSRa33kyqQTnpLthBjq
> AAAAAAA
> 15KiqGKWn0v29UYCpjrrgIlTj96Wmgo0yCFg+AAAE
> AAAAKSrXNbc4fKYnZctVOW6P8z1koqGmSqMqRM+1o18P3AAAAAA==.
> MAC does not verify: wrong MAC key?
> --
> 
> Which fails.
> 
> Can you point me to my mistake? Thank you!
> 
> Greetings Bjorn

There seems to be some kind of bug in the mail client or listserv that
messes up the data message. Attached is a text file with the actual
datamessage.

Greetings Bjorn
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