[
.B \-\-verbose
] [
.B \-\-random
filename
]
.B \e
.br
\ \ \ [
.B \-\-rounds
nr
] [
.B \-\-hostname
host ] [
.B \-\-noopt
] nbits
.br
.B ipsec
.B rsasigkey
[
.B \-\-verbose
] [
.B \-\-hostname
host ]
.B \e
.br
\ \ \ 
[
.B \-\-noopt
]
.B \-\-oldkey
file
.SH DESCRIPTION
.I Rsasigkey
generates an RSA public/private key pair,
suitable for digital signatures,
of (exactly)
.I nbits
bits (that is, two primes each of exactly
.IR nbits /2
bits,
and related numbers)
and emits it on standard output as ASCII (mostly hex) data.
.I nbits
must be a multiple of 16.
.PP
The public exponent is forced to the value
.BR 3 ,
which has important speed advantages for signature checking.
Beware that the resulting keys have known weaknesses as encryption keys
\fIand should not be used for that purpose\fR.
.PP
Normally,
.I rsasigkey
reads exactly
.I nbits
random bits from the source;
in extremely-rare circumstances it may need more.
.PP
The
.B \-\-rounds
option specifies the number of rounds to be done by the
.I mpz_probab_prime_p
probabilistic primality checker.
The default, 30, is fairly rigorous and should not normally
have to be overridden.
.PP
The
.B \-\-hostname
option specifies what host name to use in
the first line of the output (see below);
the default is what
.IR gethostname (2)
returns.
.PP
The
.B \-\-noopt
option suppresses an optimization of the private key
(to be precise, setting of the decryption exponent to
.B lcm(p\-1,q\-1)
rather than
.BR (p\-1)*(q\-1) )
which speeds up operations on it slightly
but can cause it to flunk a validity check in old RSA implementations
(notably, obsolete versions of
.IR ipsec_pluto (8)).
.PP
The
.B \-\-oldkey
option specifies that rather than generate a new key,
.I rsasigkey
should read an old key from the
.I file
(the name
.B \-
means ``standard input'')
and use that to generate its output.
Input lines which do not look like
.I rsasigkey
output are silently ignored.
This permits updating old keys to the current format.
.PP
The output format looks like this (with long numbers trimmed down
for clarity):
	Coefficient: 0xafb761d001...0c13e98d98
.fi
.PP
The first (comment) line,
indicating the nature and date of the key,
and giving a host name,
is used by
.IR ipsec_showhostkey (8)
when generating some forms of key output.
.PP
The commented-out
.B pubkey=
line contains the public key\(emthe public exponent and the modulus\(emcombined
in approximately RFC 2537 format
(the one deviation is that the combined value is given with a
.B 0s
prefix, rather than in unadorned base-64),
suitable for use in the
.I ipsec.conf
file.
.PP
The
.BR Modulus ,
.BR PublicExponent ,
and
.B PrivateExponent
lines give the basic signing and verification data.
.PP
The
.B Prime1
and
.B Prime2
lines give the primes themselves (aka
.I p
and
.IR q ),
largest first.
The
.B Exponent1
and
.B Exponent2
lines give
the private exponent mod
.IR p\-1
and
.IR q\-1
respectively.
The
.B Coefficient
line gives the Chinese Remainder Theorem coefficient,
which is the inverse of
.IR q ,
The file contents can be inserted verbatim into a suitable entry in the
.I ipsec.secrets
file (see
.IR ipsec.secrets (5)),
and the public key can then be extracted and edited into the
.I ipsec.conf
file (see
.IR ipsec.conf (5)).
.TP
.B "ipsec rsasigkey \-\-verbose \-\-oldkey oldie >latest"
takes the old signature key from file
.I oldie
and puts a version in the current format into the file
.IR latest ,
with running commentary on standard error.
.SH FILES
/dev/random
.SH SEE ALSO
random(4), ipsec_showhostkey(8)
.br
\fIApplied Cryptography\fR, 2nd. ed., by Bruce Schneier, Wiley 1996.
.br
RFCs 2537, 2313.
.br
\fIGNU MP, the GNU multiple precision arithmetic library, edition 2.0.2\fR,
by Torbj Granlund.
.SH HISTORY
Written for the Linux FreeS/WAN project



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