Class FIPS186

This method generates the DSS p, q, and g parameters only when L (the modulus length) is not one of the following: 512, 768 and 1024. For those values of L, this implementation uses pre-computed values of p, q, and g given in the document CryptoSpec included in the security guide documentation of the standard JDK distribution.

The DSS requires two primes , p and q, satisfying the following three conditions:

• 2159 < q < 2160
• 2L-1 < p < 2L for a specified L, where L = 512 + 64j for some 0 <= j <= 8
• q divides p - 1.

The algorithm used to find these primes is as described in FIPS-186, section 2.2: GENERATION OF PRIMES. This prime generation scheme starts by using the Sha160 and a user supplied SEED to construct a prime, q, in the range 2¹⁵⁹ < q < 2¹⁶⁰. Once this is accomplished, the same SEED value is used to construct an X in the range 2L-1 < X < 2L. The prime, p, is then formed by rounding X to a number congruent to 1 mod 2q. In this implementation we use the same SEED value given in FIPS-186, Appendix 5.