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.TH "opaque" "1" "" "" "simple command-line frontend for libopaque"
.hy
.SH NAME
.PP
opaque - simple command-line frontend for libopaque
.SH SYNOPSIS
.PP
Create new OPAQUE records
.PP
Create new opaque record - offline
.IP
.nf
\f[C]
echo -n password | opaque init idU idS 3>export_key [4<skS] >record
\f[R]
.fi
.PP
Initiate new online registration
.IP
.nf
\f[C]
echo -n password | opaque register >msg 3>ctx
\f[R]
.fi
.PP
Respond to new online registration request
.IP
.nf
\f[C]
opaque respond <msg >rpub 3>rsec [4<skS]
\f[R]
.fi
.PP
Finalize online registration
.IP
.nf
\f[C]
opaque finalize idU idS <ctx 4<rpub 3>export_key >record
\f[R]
.fi
.PP
Complete online record
.IP
.nf
\f[C]
opaque store <rec 3<rsec >record
\f[R]
.fi
.PP
Server portion of online registration
.IP
.nf
\f[C]
socat | opaque server-reg 3>record [4<skS]
\f[R]
.fi
.PP
User portion of online registration
.IP
.nf
\f[C]
socat | opaque user-reg idU idS 3< <(echo -n password) 4>export_key
\f[R]
.fi
.PP
Run OPAQUE
.PP
Server portion of OPAQUE session
.IP
.nf
\f[C]
socat | opaque server idU idS context 3<record 4>shared_key
\f[R]
.fi
.PP
User portion of OPAQUE session
.IP
.nf
\f[C]
socat | opaque user idU idS context 3< <(echo -n password) 4>export_key 5>shared_key [6<pkS]
\f[R]
.fi
.SH DESCRIPTION
.PP
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\[cq]t need to store any state.
The protocol has two phases:
.IP \[bu] 2
In the initialization phase a client registers with the server.
.IP \[bu] 2
In the AKE phase the client and server establish a shared secret.
.PP
The initialization only needs to be executed once, the key-exchange can
be executed as many times as necessary.
.SS Initialization
.PP
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.
.PP
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.
.SS Offline Registration
.IP
.nf
\f[C]
echo -n password | ./opaque init user server >record 3>export_key
\f[R]
.fi
.SS Online Registration
.SS socat style
.PP
On the server:
.IP
.nf
\f[C]
socat tcp-l:23523,reuseaddr,fork system:\[dq]bash -c \[rs]\[aq]opaque server-reg user server 3>record\[rs]\[aq]\[dq]
\f[R]
.fi
.PP
On the client:
.IP
.nf
\f[C]
socat tcp:127.0.0.1:23523 exec:\[aq]bash -c \[rs]\[dq]opaque user-reg user server 3< <(echo -n password) 4>export_key\[rs]\[dq]\[aq]
\f[R]
.fi
.SS tcpserver style
.PP
On the server:
.IP
.nf
\f[C]
s6-tcpserver 127.0.0.1 23523 bash -c \[aq]opaque server-reg user server 3>record\[aq]
\f[R]
.fi
.PP
On the client:
.IP
.nf
\f[C]
s6-tcpclient 127.0.0.1 23523 bash -c \[dq]opaque user-reg user server <&6 >&7 3< <(echo -n password) 4>export_key\[dq]
\f[R]
.fi
.SS Manually
.PP
It\[cq]s possible to do all 4 steps seperately, in case you cannot
connect to the server directly, then:
.PP
The user initiates with:
.IP
.nf
\f[C]
echo -n password | opaque register >msg 3>ctx
\f[R]
.fi
.PP
The server gets \f[V]msg\f[R] and responds with rpub, while keeping rsec
secret:
.IP
.nf
\f[C]
cat msg | opaque respond >rpub 3>rsec
\f[R]
.fi
.PP
The user receives \f[V]rpub\f[R] and creates stub record and optionally
uses the export key to encrypt more data:
.IP
.nf
\f[C]
cat ctx | opaque finalize user server 4<rpub >record 3>export_key
\f[R]
.fi
.PP
the server finalizes the record by completing the stub record from the
client:
.IP
.nf
\f[C]
cat rec | opaque store user server >record 3<rsec
\f[R]
.fi
.SS Running OPAQUE
.SS tcpserver style
.PP
On the server:
.IP
.nf
\f[C]
s6-tcpserver 127.0.0.1 23523 bash -c \[aq]./opaque server user server context 3<record 4>shared_secret\[aq]
\f[R]
.fi
.PP
On the client:
.IP
.nf
\f[C]
s6-tcpclient 127.0.0.1 23523 bash -c \[dq]./opaque user user server context <&6 >&7 3< <(echo -n password) 4>export_key 5>shared_secret\[dq]
\f[R]
.fi
.SS socat style
.PP
On the server:
.IP
.nf
\f[C]
socat tcp-l:23523,reuseaddr,fork system:\[dq]bash -c \[rs]\[aq]./opaque server user server context 3<record 4>shared_secret\[rs]\[aq]\[dq]
\f[R]
.fi
.PP
On the client:
.IP
.nf
\f[C]
socat tcp:127.0.0.1:23523 exec:\[aq]bash -c \[rs]\[dq]./opaque user user server context 3< <(echo -n password) 4>export_key  5>shared_secret\[rs]\[dq]\[aq]
\f[R]
.fi
.SH REPORTING BUGS
.PP
https://github.com/stef/libopaque/issues/
.SH AUTHOR
.PP
Written by Stefan Marsiske.
.SH COPYRIGHT
.PP
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.
.SH SEE ALSO
.PP
https://ctrlc.hu/\[ti]stef/blog/tags/opaque/
.PP
\f[V]socat(1)\f[R], \f[V]tcpserver(1)\f[R]