opaque(1)

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)