NAME
moduli —
system moduli file
DESCRIPTION
The
/etc/moduli file contains the system-wide Diffie-Hellman
prime moduli for
sshd(8).
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).
Time:
yyyymmddhhmmss. Specifies the
system time that the line was appended to the file. The value 00000000000000
means unknown (historic).
Type:
decimal. Specifies the
internal structure of the prime modulus.
- 0:
- unknown; often learned from peer during protocol operation,
and saved for later analysis.
- 1:
- unstructured; a common large number.
- 2:
- safe (p = 2q + 1); meets basic structural
requirements.
- 3:
- Schnorr.
- 4:
- Sophie-Germaine (q = (p-1)/2); usually generated in the
process of testing safe or strong primes.
- 5:
- strong; useful for RSA public key generation.
Tests:
decimal (bit field).
Specifies the methods used in checking for primality. Usually, more than one
test is used.
- 0:
- not tested; often learned from peer during protocol
operation, and saved for later analysis.
- 1:
- composite; failed one or more tests. In this case, the
highest bit specifies the test that failed.
- 2:
- sieve; checked for division by a range of smaller
primes.
- 4:
- Miller-Rabin.
- 8:
- Jacobi.
- 16:
- Elliptic Curve.
Tries:
decimal. Depends on the value
of the highest valid Test bit, where the method specified is:
- 0:
- not tested (always zero).
- 1:
- composite (irrelevant).
- 2:
- sieve; number of primes sieved. Commonly on the order of
32,000,000.
- 4:
- Miller-Rabin; number of M-R iterations. Commonly on the
order of 32 to 64.
- 8:
- Jacobi; unknown (always zero).
- 16:
- Elliptic Curve; unused (always zero).
Size:
decimal. Specifies the number
of the most significant bit (0 to M).
Generator:
hex string. Specifies the
best generator for a Diffie-Hellman exchange. 0 = unknown or variable, 2, 3,
5, etc.
Modulus:
hex string. The prime
modulus.
The file should be 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.
Note that
sshd(8) uses only the Size
criteria and then selects a modulus at random if more than one meet the Size
criteria.
FILES
- /etc/moduli
-
SEE ALSO
qsieve(1),
sshd(8)
HISTORY
The
moduli file appeared in
OpenBSD
2.8 and
NetBSD 1.6.