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75 lines
3.4 KiB
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75 lines
3.4 KiB
Plaintext
MODULI(5) File Formats Manual MODULI(5)
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NAME
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moduli M-bM-^@M-^S Diffie-Hellman moduli
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DESCRIPTION
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The /etc/moduli file contains prime numbers and generators for use by
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sshd(8) in the Diffie-Hellman Group Exchange key exchange method.
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New moduli may be generated with ssh-keygen(1) using a two-step process.
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An initial candidate generation pass, using ssh-keygen -G, calculates
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numbers that are likely to be useful. A second primality testing pass,
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using ssh-keygen -T, provides a high degree of assurance that the numbers
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are prime and are safe for use in Diffie-Hellman operations by sshd(8).
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This moduli format is used as the output from each pass.
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The file consists of newline-separated records, one per modulus,
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containing seven space-separated fields. These fields are as follows:
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timestamp The time that the modulus was last processed as
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YYYYMMDDHHMMSS.
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type Decimal number specifying the internal structure of
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the prime modulus. Supported types are:
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0 Unknown, not tested.
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2 "Safe" prime; (p-1)/2 is also prime.
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4 Sophie Germain; 2p+1 is also prime.
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Moduli candidates initially produced by ssh-keygen(1)
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are Sophie Germain primes (type 4). Further primality
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testing with ssh-keygen(1) produces safe prime moduli
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(type 2) that are ready for use in sshd(8). Other
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types are not used by OpenSSH.
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tests Decimal number indicating the type of primality tests
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that the number has been subjected to represented as a
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bitmask of the following values:
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0x00 Not tested.
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0x01 Composite number M-bM-^@M-^S not prime.
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0x02 Sieve of Eratosthenes.
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0x04 Probabilistic Miller-Rabin primality tests.
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The ssh-keygen(1) moduli candidate generation uses the
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Sieve of Eratosthenes (flag 0x02). Subsequent
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ssh-keygen(1) primality tests are Miller-Rabin tests
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(flag 0x04).
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trials Decimal number indicating the number of primality
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trials that have been performed on the modulus.
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size Decimal number indicating the size of the prime in
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bits.
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generator The recommended generator for use with this modulus
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(hexadecimal).
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modulus The modulus itself in hexadecimal.
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When performing Diffie-Hellman Group Exchange, sshd(8) first estimates
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the size of the modulus required to produce enough Diffie-Hellman output
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to sufficiently key the selected symmetric cipher. sshd(8) then randomly
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selects a modulus from /etc/moduli that best meets the size requirement.
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SEE ALSO
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ssh-keygen(1), sshd(8)
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STANDARDS
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M. Friedl, N. Provos, and W. Simpson, Diffie-Hellman Group Exchange for
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the Secure Shell (SSH) Transport Layer Protocol, RFC 4419, March 2006,
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2006.
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OpenBSD 5.8 September 26, 2012 OpenBSD 5.8
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