An Extended Quadratic Frobenius Primality Test with Average Case Error
Estimates
Ivan Bjerre Damgård
November 2001 |

## Abstract:
We present an Extended Quadratic Frobenius Primality Test
(EQFT), which is related to the Miller-Rabin test and the Quadratic Frobenius
test (QFT) by Grantham. EQFT is well-suited for generating large, random
prime numbers since on a random input number, it takes time about equivalent
to 2 Miller-Rabin tests, but has much smaller error probability. EQFT extends
QFT by verifying additional algebraic properties related to the existence of
elements of order 3 and 4. We obtain a simple closed expression that upper
bounds the probability of acceptance for any input number. This in turn
allows us to give strong bounds on the average-case behaviour of the test:
consider the algorithm that repeatedly chooses random odd bit numbers,
subjects them to iterations of our test and outputs the first one found
that passes all tests. We obtain numeric upper bounds for the error
probability of this algorithm as well as a general closed expression bounding
the error. For instance, it is at most for . Compared
to earlier similar results for the Miller-Rabin test, the results indicates
that our test in the average case has the effect of 9 Miller-Rabin tests,
while only taking time equivalent to about 2 such tests. We also give bounds
for the error in case a prime is sought by incremental search from a random
starting point. While EQFT is slower than the average case on a small set of
inputs, we present a variant that is always fast, i.e. takes time about 2
Miller-Rabin tests. The variant has slightly larger worst case error
probability than EQFT, but still improves on previous proposed
tests
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Last modified: 2003-06-08 by webmaster.