.Dd April 15, 1997
.Dt SECRETSPLIT 1
.Os NetBSD 1.2BETA
.Sh NAME
.Nm secretsplit
.Nd secret-splitting program
.Sh SYNOPSIS
.Nm
.Fl s
.Op Fl i
.Op Fl I
.Op Fl v Ns Op Cm v...
.Ar secret
.Ar modulus
.Ar totalparts
.Ar minparts
.br
.Nm
.Fl m
.Op Fl b Ns Ar N
.Op Fl x
.Op Fl v Ns Op Cm v...
.Ar part ...
.Sh DESCRIPTION
.Nm
implements secret-splitting.
.Pp
In its first form, with
.Fl s ,
.Nm
splits
.Ar secret
into
.Ar totalparts
parts, of which any
.Ar minparts
will suffice to reconstruct the secret.
.Ar modulus
must be a prime larger than
.Ar secret ;
see
.Xr bigprime 1 .
The resulting parts are output, one per line, in a format private to
.\" Why doesn't ".Nm ;" work right?
.Nm secretsplit ;
all that is promised about this format is that the only characters that
will appear in a part are digits and lowercase letters.  The arguments
are simply numbers; by default they are in decimal, but a leading
.Li 0x
or
.Li 0X
will indicate hexadecimal, and a leading
.Li 0
will indicate octal.  Other bases can be used as well by prefixing the
base, expressed in decimal, surrounded by colons, to the number; bases
can range from 2 through 36.  For example, all of these specify the
same number:
.Bd -literal
	011145401322
	1234567890
	0x499602d2
	:23:87ifcgi
	:36:kf12oi
.Ed
.Nm
needs to generate random numbers; it obtains the necessary entropy by
running various system utilities, such as
.Xr ps 1
and
.Xr netstat 1 ;
if
.Fl i
is given, it also reads its standard input to EOF and uses that as
additional random-number seed data.  If
.Fl I
is given, standard input is read and the other sources are ignored.
This is emphatically not recommended; the option exists for people who
have a relatively high-bandwidth source of strong random bits and don't
want to (or can't) wait for the normal randomness-gathering process.
.Pp
The second form, with
.Fl m ,
is used to reconstruct the secret.  One or more
.Ar part Ns s
must be given on the command line;
.Nm
will reconstruct the secret that was given when the parts were
generated, if enough parts are provided.  If more parts are given than
are needed,
.Nm
will check that all the parts match.  If too few parts are given,
.Nm
cannot reconstruct the secret, and will print a message saying so.
In any case, some consistency checks are possible, such as checking
that all parts given were generated with identical
.Ar modulus
values; these are always done, and if they fail, an error is produced
and nothing further is done no matter how many parts are given.
.Pp
When reconstructing a secret, by default, the recovered secret is
output in decimal.  Specifying
.Fl b Ns Ar N
produces output in base
.Ar N
instead;
.Fl x
is an abbreviation for
.Fl b Ns Ar 16 .
.Pp
If both
.Fl s
and
.Fl m
are given, operation is controlled by whichever one appears last on the
command line.
.Pp
The
.Fl v
option makes
.Nm
verbose, producing messages on stderr describing its progress.
Multiple
.Fl v
options increase the level of chattiness.
.Sh BUGS
When splitting, if
.Ar modulus
is not a prime,
.Nm
the resulting parts may be useless; it will not necessarily be possible
to uniquely reconstruct the secret from the generated parts.
.Nm
does not check for this condition, since it is relatively expensive to
do so.
.Sh AUTHOR
der Mouse,
.Aq mouse@rodents.montreal.qc.ca .