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127 lines
3.6 KiB
127 lines
3.6 KiB
.\" $OpenBSD: moduli.5,v 1.17 2012/09/26 17:34:38 jmc Exp $ |
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.\" |
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.\" Copyright (c) 2008 Damien Miller <djm@mindrot.org> |
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.\" |
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.\" Permission to use, copy, modify, and distribute this software for any |
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.\" purpose with or without fee is hereby granted, provided that the above |
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.\" copyright notice and this permission notice appear in all copies. |
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.\" |
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR |
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF |
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
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.Dd $Mdocdate: September 26 2012 $ |
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.Dt MODULI 5 |
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.Os |
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.Sh NAME |
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.Nm moduli |
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.Nd Diffie-Hellman moduli |
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.Sh DESCRIPTION |
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The |
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.Pa /etc/moduli |
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file contains prime numbers and generators for use by |
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.Xr sshd 8 |
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in the Diffie-Hellman Group Exchange key exchange method. |
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.Pp |
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New moduli may be generated with |
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.Xr ssh-keygen 1 |
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using a two-step process. |
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An initial |
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.Em candidate generation |
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pass, using |
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.Ic ssh-keygen -G , |
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calculates numbers that are likely to be useful. |
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A second |
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.Em primality testing |
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pass, using |
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.Ic ssh-keygen -T , |
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provides a high degree of assurance that the numbers are prime and are |
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safe for use in Diffie-Hellman operations by |
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.Xr sshd 8 . |
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This |
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.Nm |
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format is used as the output from each pass. |
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.Pp |
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The file consists of newline-separated records, one per modulus, |
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containing seven space-separated fields. |
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These fields are as follows: |
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.Bl -tag -width Description -offset indent |
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.It timestamp |
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The time that the modulus was last processed as YYYYMMDDHHMMSS. |
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.It type |
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Decimal number specifying the internal structure of the prime modulus. |
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Supported types are: |
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.Pp |
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.Bl -tag -width 0x00 -compact |
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.It 0 |
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Unknown, not tested. |
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.It 2 |
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"Safe" prime; (p-1)/2 is also prime. |
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.It 4 |
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Sophie Germain; 2p+1 is also prime. |
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.El |
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.Pp |
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Moduli candidates initially produced by |
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.Xr ssh-keygen 1 |
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are Sophie Germain primes (type 4). |
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Further primality testing with |
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.Xr ssh-keygen 1 |
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produces safe prime moduli (type 2) that are ready for use in |
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.Xr sshd 8 . |
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Other types are not used by OpenSSH. |
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.It tests |
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Decimal number indicating the type of primality tests that the number |
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has been subjected to represented as a bitmask of the following values: |
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.Pp |
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.Bl -tag -width 0x00 -compact |
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.It 0x00 |
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Not tested. |
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.It 0x01 |
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Composite number \(en not prime. |
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.It 0x02 |
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Sieve of Eratosthenes. |
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.It 0x04 |
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Probabilistic Miller-Rabin primality tests. |
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.El |
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.Pp |
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The |
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.Xr ssh-keygen 1 |
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moduli candidate generation uses the Sieve of Eratosthenes (flag 0x02). |
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Subsequent |
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.Xr ssh-keygen 1 |
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primality tests are Miller-Rabin tests (flag 0x04). |
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.It trials |
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Decimal number indicating the number of primality trials |
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that have been performed on the modulus. |
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.It size |
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Decimal number indicating the size of the prime in bits. |
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.It generator |
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The recommended generator for use with this modulus (hexadecimal). |
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.It modulus |
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The modulus itself in hexadecimal. |
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.El |
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.Pp |
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When performing Diffie-Hellman Group Exchange, |
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.Xr sshd 8 |
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first estimates the size of the modulus required to produce enough |
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Diffie-Hellman output to sufficiently key the selected symmetric cipher. |
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.Xr sshd 8 |
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then randomly selects a modulus from |
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.Fa /etc/moduli |
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that best meets the size requirement. |
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.Sh SEE ALSO |
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.Xr ssh-keygen 1 , |
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.Xr sshd 8 |
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.Sh STANDARDS |
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.Rs |
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.%A M. Friedl |
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.%A N. Provos |
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.%A W. Simpson |
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.%D March 2006 |
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.%R RFC 4419 |
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.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol |
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.%D 2006 |
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.Re
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