.\" $OpenBSD: moduli.5,v 1.10 2005/02/21 10:22:04 djm Exp $
.\"
.\" Copyright 1997, 2000 William Allen Simpson <wsimpson@greendragon.com>
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.\" Manual page, using -mandoc macros
.\"
.Dd July 28, 1997
.Dt MODULI 5
.Os
.Sh NAME
.Nm moduli
.Nd system moduli file
.Sh DESCRIPTION
The
.Pa /etc/moduli
file contains the system-wide Diffie-Hellman prime moduli for
.Xr sshd 8 .
.Pp
Each line in this file contains the following fields:
Time, Type, Tests, Tries, Size, Generator, Modulus.
The fields are separated by white space (tab or blank).
.Pp
.Fa Time : yyyymmddhhmmss .
Specifies the system time that the line was appended to the file.
The value 00000000000000 means unknown (historic).
.\"The file is sorted in ascending order.
.Pp
.Fa Type : decimal .
Specifies the internal structure of the prime modulus.
.Pp
.Bl -tag -width indent -offset indent -compact
.It 0 :
unknown;
often learned from peer during protocol operation,
and saved for later analysis.
.It 1 :
unstructured;
a common large number.
.It 2 :
safe (p = 2q + 1);
meets basic structural requirements.
.It 3 :
Schnorr.
.It 4 :
Sophie-Germain (q = (p-1)/2);
usually generated in the process of testing safe or strong primes.
.It 5 :
strong;
useful for RSA public key generation.
.El
.Pp
.Fa Tests : decimal (bit field) .
Specifies the methods used in checking for primality.
Usually, more than one test is used.
.Pp
.Bl -tag -width indent -offset indent -compact
.It 0 :
not tested;
often learned from peer during protocol operation,
and saved for later analysis.
.It 1 :
composite;
failed one or more tests.
In this case, the highest bit specifies the test that failed.
.It 2 :
sieve;
checked for division by a range of smaller primes.
.It 4 :
Miller-Rabin.
.It 8 :
Jacobi.
.It 16 :
Elliptic Curve.
.El
.Pp
.Fa Tries : decimal .
Depends on the value of the highest valid Test bit,
where the method specified is:
.Pp
.Bl -tag -width indent -offset indent -compact
.It 0 :
not tested
(always zero).
.It 1 :
composite
(irrelevant).
.It 2 :
sieve;
number of primes sieved.
Commonly on the order of 32,000,000.
.It 4 :
Miller-Rabin;
number of M-R iterations.
Commonly on the order of 32 to 64.
.It 8 :
Jacobi;
unknown
(always zero).
.It 16 :
Elliptic Curve;
unused
(always zero).
.El
.Pp
.Fa Size : decimal .
Specifies the number of the most significant bit (0 to M).
.Pp
.Fa Generator : hex string .
Specifies the best generator for a Diffie-Hellman exchange.
0 = unknown or variable,
2, 3, 5, etc.
.Pp
.Fa Modulus : hex string .
The prime modulus.
.Pp
The file is searched for moduli that meet the appropriate
Time, Size and Generator criteria.
When more than one meet the criteria,
the selection should be weighted toward newer moduli,
without completely disqualifying older moduli.
.Pp
New moduli may be generated using the
.Xr ssh-keygen 1
tool.
.Sh FILES
.Bl -tag -width /etc/moduli -compact
.It Pa /etc/moduli
.El
.Sh SEE ALSO
.Xr ssh-keygen 1 ,
.Xr sshd 8