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IPSEC_RSASIGKEY

Section: Maintenance Commands (8)
Updated: 15 April 2000
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NAME

ipsec rsasigkey - generate RSA signature key

SYNOPSIS

ipsec rsasigkey [ --verbose ] [ --random filename ]
[ --rounds nr ] nbits
ipsec rsasigkey [ --verbose ] --oldkey file

DESCRIPTION

Rsasigkey generates an RSA public/private key pair, suitable for digital signatures, of (exactly) nbits bits (that is, two primes each of exactly nbits/2 bits, and related numbers) and emits it on standard output as ASCII (mostly hex) data. nbits must be a multiple of 16.

The public exponent is forced to the value 3, which has important speed advantages for signature checking. Beware that the resulting keys have known weaknesses as encryption keys and should not be used for that purpose.

The --verbose option makes rsasigkey give a running commentary on standard error. By default, it works in silence until it is ready to generate output.

The --random option specifies a source for random bits. The default is /dev/random (see random(4)). Normally, rsasigkey reads exactly nbits random bits from the source; in extremely-rare circumstances it may need more.

The --rounds option specifies the number of rounds to be done by the mpz_probab_prime_p probabilistic primality checker. The default, 30, is fairly rigorous and should not normally have to be overridden.

The --oldkey option specifies that rather than generate a new key, rsasigkey should read an old key from the file (lines which do not look like rsasigkey output are silently ignored) and use that to generate its output. This permits updating old keys to the current format.

The output format looks like this (with long numbers trimmed down for clarity):

        # 1024 bits, Sat Apr 15 13:53:22 2000
        # for signatures only, UNSAFE FOR ENCRYPTION
        #pubkey=0x0103cc2a86fcf440...cf1011abb82d1
        #IN KEY 0x4200 4 1 AQOF8tZ2NZt...Y1P+buFuFn/
        # (0x4200 = auth-only host-level, 4 = IPSec, 1 = RSA)
        Modulus: 0xcc2a86fcf440...cf1011abb82d1
        PublicExponent: 0x03
        # everything after this point is secret
        PrivateExponent: 0x881c59fdf8...ab05c8c77d23
        Prime1: 0xf49fd1f779...46504c7bf3
        Prime2: 0xd5a9108453...321d43cb2b
        Exponent1: 0xa31536a4fb...536d98adda7f7
        Exponent2: 0x8e70b5ad8d...9142168d7dcc7
        Coefficient: 0xafb761d001...0c13e98d98

The commented-out pubkey= line contains the public key---the public exponent and the modulus---combined in approximately RFC 2537 format (the one deviation is that the combined value is given in hex with a 0x prefix, rather than in unadorned base-64), suitable for use in the ipsec.conf file.

The commented-out IN KEY line contains the public key in exactly RFC 2537 format (except for the lack of a name on the front), suitable for use in DNS zone files. The flags, algorithm, and protocol fields are given numerically, with an accompanying explanation, because some incomplete early implementations of the KEY record (e.g., BIND 8.2.2-P5) don't support more mnemonic syntax.

The Modulus, PublicExponent, and PrivateExponent lines give the basic signing and verification data.

The Prime1 and Prime2 lines give the primes themselves (aka p and q), largest first. The Exponent1 and Exponent2 lines give the private exponent mod p-1 and q-1 respectively. The Coefficient line gives the Chinese Remainder Theorem coefficient, which is the inverse of q, mod p. These additional numbers (which must all be kept as secret as the private exponent) are precomputed aids to rapid signature generation.

No attempt is made to break long lines.

EXAMPLES

ipsec rsasigkey --verbose 1024 >mykey: generates a 1024-bit signature key and puts it in the file mykey, with running commentary on standard error. The file contents can be inserted verbatim into a suitable entry in the ipsec.secrets file (see ipsec.secrets(5)), and the public key can then be extracted and edited into the ipsec.conf file (see ipsec.conf(5)).
ipsec rsasigkey --verbose --oldkey oldie >latest: takes the old signature key from file oldie and puts a version in the current format into the file latest, with running commentary on standard error.

FILES

/dev/random

HISTORY

Written for the Linux FreeS/WAN project <http://www.xs4all.nl/~freeswan/> by Henry Spencer.

BUGS

There is an internal limit on nbits, currently 4096.

Rsasigkey's run time is difficult to predict, since /dev/random output can be arbitrarily delayed if the system's entropy pool is low on randomness, and the time taken by the search for primes is also somewhat unpredictable. A reasonably typical time for a 1024-bit key on a 200MHz Pentium MMX with plenty of randomness available is 20 seconds, almost all of it in the prime searches.

The --oldkey option does not check its input format as rigorously as it might. Corrupted rsasigkey output may confuse it.

There ought to be a convenient way to take --oldkey input from standard input.

This program makes no use of code furnished by RSA Data Security Inc. or Public Key Partners. However, the techniques used would appear to be covered (in the USA) by the US patent on the RSA algorithm, which expires 20 Sept 2000.

This document was created by man2html, using the manual pages.
Time: 04:38:15 GMT, May 22, 2000