This paper presents further improvements in the transformation of the Discrete Logarithm Problem (DLP) and Elliptic Curve Discrete Logarithm Problem (ECDLP) over prime fields to the Quadratic Unconstrained Binary Optimization (QUBO) problem. This is significant from a cryptanalysis standpoint, as QUBO problems may be solved using quantum annealers, and the fewer variables the resulting QUBO problem has, the less time is expected to obtain a solution.The main idea presented in the paper is allowing the representation of the exponent in different bases than the typically used base 2 (binary representation). It is shown that in such cases, the reduction of the discrete logarithm problem over the prime field
Fp to the QUBO problem may be obtained using approximately
1.89n2 logical variables for
n being the bitlength of prime
p, instead of the
2n2 which was previously the best-known reduction method. The paper provides a practical example using the given method to solve the discrete logarithm problem over the prime field
F47. Similarly, for the elliptic curve discrete logarithm problem over the prime field
Fp, allowing the representation of the exponent in different bases than typically used base two results in a lower number of required logical variables for
n being the bitlength of prime
p, from
3n3 to
log2(43n)6n3 logical variables, in the case of Edwards curves.