moduli.0 revision 218769
1MODULI(5) OpenBSD Programmer's Manual MODULI(5) 2 3NAME 4 moduli - Diffie Hellman moduli 5 6DESCRIPTION 7 The /etc/moduli file contains prime numbers and generators for use by 8 sshd(8) in the Diffie-Hellman Group Exchange key exchange method. 9 10 New moduli may be generated with ssh-keygen(1) using a two-step process. 11 An initial candidate generation pass, using ssh-keygen -G, calculates 12 numbers that are likely to be useful. A second primality testing pass, 13 using ssh-keygen -T provides a high degree of assurance that the numbers 14 are prime and are safe for use in Diffie Hellman operations by sshd(8). 15 This moduli format is used as the output from each pass. 16 17 The file consists of newline-separated records, one per modulus, 18 containing seven space separated fields. These fields are as follows: 19 20 timestamp The time that the modulus was last processed as 21 YYYYMMDDHHMMSS. 22 23 type Decimal number specifying the internal structure of 24 the prime modulus. Supported types are: 25 26 0 Unknown, not tested 27 2 "Safe" prime; (p-1)/2 is also prime. 28 4 Sophie Germain; (p+1)*2 is also prime. 29 30 Moduli candidates initially produced by ssh-keygen(1) 31 are Sophie Germain primes (type 4). Futher primality 32 testing with ssh-keygen(1) produces safe prime moduli 33 (type 2) that are ready for use in sshd(8). Other 34 types are not used by OpenSSH. 35 36 tests Decimal number indicating the type of primality tests 37 that the number has been subjected to represented as a 38 bitmask of the following values: 39 40 0x00 Not tested 41 0x01 Composite number - not prime. 42 0x02 Sieve of Eratosthenes 43 0x04 Probabalistic Miller-Rabin primality tests. 44 45 The ssh-keygen(1) moduli candidate generation uses the 46 Sieve of Eratosthenes (flag 0x02). Subsequent 47 ssh-keygen(1) primality tests are Miller-Rabin tests 48 (flag 0x04). 49 50 trials Decimal number indicating of primaility trials that 51 have been performed on the modulus. 52 53 size Decimal number indicating the size of the prime in 54 bits. 55 56 generator The recommended generator for use with this modulus 57 (hexadecimal). 58 59 modulus The modulus itself in hexadecimal. 60 61 When performing Diffie Hellman Group Exchange, sshd(8) first estimates 62 the size of the modulus required to produce enough Diffie Hellman output 63 to sufficiently key the selected symmetric cipher. sshd(8) then randomly 64 selects a modulus from /etc/moduli that best meets the size requirement. 65 66SEE ALSO 67 ssh-keygen(1), sshd(8), 68 69 Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer 70 Protocol, RFC 4419, 2006. 71 72OpenBSD 4.9 June 26, 2008 OpenBSD 4.9 73