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moduli(5) [netbsd man page]

MODULI(5)						      BSD File Formats Manual							 MODULI(5)

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.

BSD
								 February 7, 2005							       BSD

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MODULI(5)						      BSD File Formats Manual							 MODULI(5)

NAME

     moduli -- Diffie-Hellman moduli

DESCRIPTION

     The /etc/moduli file contains prime numbers and generators for use by sshd(8) in the Diffie-Hellman Group Exchange key exchange method.

     New moduli may be generated with ssh-keygen(1) using a two-step process.  An initial candidate generation pass, using ssh-keygen -G, calcu-
     lates numbers that are likely to be useful.  A second primality testing pass, using ssh-keygen -T, provides a high degree of assurance that
     the numbers are prime and are safe for use in Diffie-Hellman operations by sshd(8).  This moduli format is used as the output from each pass.

     The file consists of newline-separated records, one per modulus, containing seven space-separated fields.	These fields are as follows:

	   timestamp	The time that the modulus was last processed as YYYYMMDDHHMMSS.

	   type 	Decimal number specifying the internal structure of the prime modulus.	Supported types are:

			0     Unknown, not tested.
			2     "Safe" prime; (p-1)/2 is also prime.
			4     Sophie Germain; 2p+1 is also prime.

			Moduli candidates initially produced by ssh-keygen(1) are Sophie Germain primes (type 4).  Further primality testing with
			ssh-keygen(1) produces safe prime moduli (type 2) that are ready for use in sshd(8).  Other types are not used by OpenSSH.

	   tests	Decimal number indicating the type of primality tests that the number has been subjected to represented as a bitmask of
			the following values:

			0x00  Not tested.
			0x01  Composite number - not prime.
			0x02  Sieve of Eratosthenes.
			0x04  Probabilistic Miller-Rabin primality tests.

			The ssh-keygen(1) moduli candidate generation uses the Sieve of Eratosthenes (flag 0x02).  Subsequent ssh-keygen(1) pri-
			mality tests are Miller-Rabin tests (flag 0x04).

	   trials	Decimal number indicating the number of primality trials that have been performed on the modulus.

	   size 	Decimal number indicating the size of the prime in bits.

	   generator	The recommended generator for use with this modulus (hexadecimal).

	   modulus	The modulus itself in hexadecimal.

     When performing Diffie-Hellman Group Exchange, sshd(8) first estimates the size of the modulus required to produce enough Diffie-Hellman out-
     put to sufficiently key the selected symmetric cipher.  sshd(8) then randomly selects a modulus from /etc/moduli that best meets the size
     requirement.

SEE ALSO

     ssh-keygen(1), sshd(8)

STANDARDS

     M. Friedl, N. Provos, and W. Simpson, Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol, RFC 4419, March 2006
     2006.

BSD
								September 26, 2012							       BSD
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