IPSEC_RSASIGKEY - Online Linux Manual PageSection : 8
Updated : 10/04/2017
Source : libreswan
Note : Executable programs

NAMEipsec_rsasigkey − generate RSA signature key

SYNOPSISipsec rsasigkey [−−verbose] [−−seeddev device] [−−seed numbits] [−−configdir nssdbdir] [−−password nsspassword] [−−hostname hostname] [nbits]

DESCRIPTIONRsasigkey 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 −−seeddev option specifies a source for random bits used to seed the crypto library´s RNG​. The default is /dev/random (see random(4))​. FreeS/WAN and Openswan without NSS support used this option to specify the random source used to directly create keys​. Libreswan only uses it to seed the NSS crypto libraries RNG​. Under Linux with hardware random support, special devices might show up as /dev/*rng* devices​. However, these should never be accessed directly using this option, as hardware failures could lead to extremely non−random values (streams of zeroes have been observed in the wild) The −−seedbits option specifies how many seed bits are pulled from the random device to seed the NSS PRNG​. The default of 480bit comes from FIPS requirements​. Seed bits are rounded up to a multiple of 8​. The use of a different random device or a reduction of seedbits from the default value is prevented when the system is running in FIPS mode​. The −−configdir option specifies the nss configuration directory to use​. This is the directory where the NSS certificate, key and security modules databases reside​. The default value is /etc/ipsec​.d​. The −−password option specifies the nss cryptographic module authentication password if the NSS module has been configured to require it​. A password is required by hardware tokens and also by the internal software token module when configured to run in FIPS mode​. If the argument is configdir/nsspassword, the password comes from that file; otherwise argument is the password​. The −−hostname option specifies what host name to use in the first line of the output (see below); the default is what gethostname(2) returns​. The output format looks like this (with long numbers trimmed down for clarity): # RSA 2048 bits xy​.example​.com Sat Apr 15 13:53:22 2000 # for signatures only, UNSAFE FOR ENCRYPTION #pubkey=0sAQOF8tZ2NZt​.​.​.Y1P+buFuFn/ 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 first (comment) line, indicating the nature and date of the key, and giving a host name, is used by ipsec_showhostkey(8) when generating some forms of key output​. 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 with a 0s prefix, rather than in unadorned base−64), suitable for use in the ipsec​.conf file​. 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​. When NSS is used, these values are not available outside the NSS security database (software token or hardware token) and are instead filled in with the CKA_ID​. No attempt is made to break long lines​. The US patent on the RSA algorithm expired 20 Sept 2000​.

EXAMPLESipsec rsasigkey −−verbose 4096 >mykey​.txt generates a 4096−bit signature key and puts it in the file mykey​.txt, 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 (see ipsec_showhostkey(8))​.

FILES/dev/random, /dev/urandom

SEE ALSOrandom(4), rngd(8), ipsec_showhostkey(8), Applied Cryptography, 2nd​. ed​., by Bruce Schneier, Wiley 1996, RFCs 2537, 2313, GNU MP, the GNU multiple precision arithmetic library, edition 2​.0​.2, by Torbj Granlund

HISTORYOriginally written for the Linux FreeS/WAN project <http://www​.freeswan​.org> by Henry Spencer​. Updated for the Libreswan Project by Paul Wouters​. The −−round and −−noopt options were obsoleted as these were only used with the old non−library crypto code The −−random device is only used for seeding the crypto library, not for direct random to generate keys

BUGSThere is an internal limit on nbits, currently 20000​. 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​. Specifically, embedded systems and most virtual machines are low on entropy​. In such a situation, consider generating the RSA key on another machine, and copying ipsec​.secrets and the ipsec​.d/*db files to the embedded platform​. Note that NSS embeds the full path in the DB files, so the path on proxy machine must be identical to the path on the destination machine​.

AUTHORPaul Wouters placeholder to suppress warning
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Johanes Gumabo
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