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MODULI(5)		  FreeBSD File Formats Manual		     MODULI(5)

     moduli -- Diffie-Hellman moduli

     The /etc/ssh/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,	calculates
     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, contain-
     ing seven space-separated fields.	These fields are as follows:

	   timestamp	The time that the modulus was last processed as	YYYYM-

	   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) primality	tests are Miller-Rabin tests
			(flag 0x04).

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

	   size		Decimal	number indicating the size of the prime	in

	   generator	The recommended	generator for use with this modulus

	   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 output
     to	sufficiently key the selected symmetric	cipher.	 sshd(8) then randomly
     selects a modulus from /etc/ssh/moduli that best meets the	size require-

     ssh-keygen(1), sshd(8)

     Diffie-Hellman Group Exchange for the Secure Shell	(SSH) Transport	Layer
     Protocol, RFC 4419, 2006.

FreeBSD	13.0			 July 19, 2012			  FreeBSD 13.0


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