NAME

       opaque - simple command-line frontend for libopaque

SYNOPSIS

       Create new OPAQUE records

       Create new opaque record - offline

              echo -n password | opaque init idU idS 3>export_key [4<skS] >record

       Initiate new online registration

              echo -n password | opaque register >msg 3>ctx

       Respond to new online registration request

              opaque respond <msg >rpub 3>rsec [4<skS]

       Finalize online registration

              opaque finalize idU idS <ctx 4<rpub 3>export_key >record

       Complete online record

              opaque store <rec 3<rsec >record

       Server portion of online registration

              socat | opaque server-reg 3>record [4<skS]

       User portion of online registration

              socat | opaque user-reg idU idS 3< <(echo -n password) 4>export_key

       Run OPAQUE

       Server portion of OPAQUE session

              socat | opaque server idU idS context 3<record 4>shared_key

       User portion of OPAQUE session

              socat | opaque user idU idS context 3< <(echo -n password) 4>export_key 5>shared_key [6<pkS]

DESCRIPTION

       The  OPAQUE protocol is an asymmetric password-authenticated key-exchange.  Essentially it
       allows a client to establish a shared  secret  with  a  server  based  on  only  having  a
       password.  The client doesn’t need to store any state.  The protocol has two phases:

       • In the initialization phase a client registers with the server.

       • In the AKE phase the client and server establish a shared secret.

       The  initialization  only  needs  to be executed once, the key-exchange can be executed as
       many times as necessary.

   Initialization
       Initializing OPAQUE (registration) can be done  either  online  or  offline.   The  online
       variant  has  the  benefit that the server never learns anything about the users password,
       with the drawback that this requires 3 messages to be exchanged  by  the  client  and  the
       server.

       The  offline  initialization  is  much  easier, however either the user learns the servers
       secret, or the server learns the users password.  The  latter  might  be  useful  if  some
       organisation   wants  to  enforce  some  password  quality  rules  and  check  those  upon
       registration.  The drawback is that either way, some sensitive information  leaks  to  the
       other party.

   Offline Registration
              echo -n password | ./opaque init user server >record 3>export_key

   Online Registration
   socat style
       On the server:

              socat tcp-l:23523,reuseaddr,fork system:"bash -c \'opaque server-reg user server 3>record\'"

       On the client:

              socat tcp:127.0.0.1:23523 exec:'bash -c \"opaque user-reg user server 3< <(echo -n password) 4>export_key\"'

   tcpserver style
       On the server:

              s6-tcpserver 127.0.0.1 23523 bash -c 'opaque server-reg user server 3>record'

       On the client:

              s6-tcpclient 127.0.0.1 23523 bash -c "opaque user-reg user server <&6 >&7 3< <(echo -n password) 4>export_key"

   Manually
       It’s  possible  to  do  all  4  steps seperately, in case you cannot connect to the server
       directly, then:

       The user initiates with:

              echo -n password | opaque register >msg 3>ctx

       The server gets msg and responds with rpub, while keeping rsec secret:

              cat msg | opaque respond >rpub 3>rsec

       The user receives rpub and creates stub record and  optionally  uses  the  export  key  to
       encrypt more data:

              cat ctx | opaque finalize user server 4<rpub >record 3>export_key

       the server finalizes the record by completing the stub record from the client:

              cat rec | opaque store user server >record 3<rsec

   Running OPAQUE
   tcpserver style
       On the server:

              s6-tcpserver 127.0.0.1 23523 bash -c './opaque server user server context 3<record 4>shared_secret'

       On the client:

              s6-tcpclient 127.0.0.1 23523 bash -c "./opaque user user server context <&6 >&7 3< <(echo -n password) 4>export_key 5>shared_secret"

   socat style
       On the server:

              socat tcp-l:23523,reuseaddr,fork system:"bash -c \'./opaque server user server context 3<record 4>shared_secret\'"

       On the client:

              socat tcp:127.0.0.1:23523 exec:'bash -c \"./opaque user user server context 3< <(echo -n password) 4>export_key  5>shared_secret\"'

REPORTING BUGS

       https://github.com/stef/libopaque/issues/

AUTHOR

       Written by Stefan Marsiske.

COPYRIGHT

       Copyright  ©  2023  Stefan  Marsiske.   License LGPLv3+: GNU Lesser GPL version 3 or later
       <https://gnu.org/licenses/lgpl.html>.  This is free software: you are free to  change  and
       redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       https://ctrlc.hu/~stef/blog/tags/opaque/

       socat(1), tcpserver(1)

                                                                                        opaque(1)