freebsd-nq/share/man/man5/moduli.5

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.Dd July 28, 1997
.Dt MODULI 5
.Os
.Sh NAME
.Nm moduli
.Nd system moduli file
.Sh DESCRIPTION
The
.Nm
file contains the system-wide Diffie-Hellman prime moduli for the
.Xr photurisd 8
and
.Xr sshd 8
programs.
.Pp
Each line in this file contains the following fields:
.Va Time , Type , Tests , Tries , Size , Generator ,
and
.Va Modulus .
The fields are separated by white space (tab or blank).
.Bl -tag -width indent
.It Va Time Pq Vt 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.
.It Va Type Pq Vt decimal
Specifies the internal structure of the prime modulus.
.Pp
.Bl -tag -width 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-Germaine (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
.It Xo
.Va Tests Pq Vt decimal
(bit field)
.Xc
Specifies the methods used in checking for primality.
Usually, more than one test is used.
.Pp
.Bl -tag -width 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
.It Va Tries Pq Vt decimal
Depends on the value of the highest valid Test bit,
where the method specified is:
.Pp
.Bl -tag -width 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
.It Va Size Pq Vt decimal
Specifies the number of significant bits.
.It Va Generator Pq Vt "hex string"
Specifies the best generator for a Diffie-Hellman exchange.
0 = unknown or variable,
2, 3, 5, etc.
.It Va Modulus Pq Vt "hex string"
The prime modulus.
.El
.Pp
The file is searched for moduli that meet the appropriate
.Va Time , Size
and
.Va Generator
criteria.
When more than one meet the criteria,
the selection should be weighted toward newer moduli,
without completely disqualifying older moduli.
.Sh FILES
.Bl -tag -width ".Pa /etc/ssh/moduli" -compact
.It Pa /etc/ssh/moduli
.El
.Sh SEE ALSO
.Xr photurisd 8 ,
.Xr sshd 8