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openssh-client_5.9p1-5ubuntu1_amd64 **NAME**

**moduli** — Diffie-Hellman moduli

**DESCRIPTION**

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, 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; (p+1)*2 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 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 output to sufficiently key the selected
symmetric cipher. sshd(8) then randomly selects a modulus from __/etc/ssh/moduli__ that best
meets the size requirement.

**SEE** **ALSO**

ssh-keygen(1), sshd(8)
__Diffie-Hellman__ __Group__ __Exchange__ __for__ __the__ __Secure__ __Shell__ __(SSH)__ __Transport__ __Layer__ __Protocol__, RFC 4419,
2006.