Of course, much larger values of "a", "b", and "p" would be needed to make this example secure, since there are only 23 possible results of "n" mod 23. However, if "p" is a prime of at least 600 digits, then even the fastest modern computers using the fastest known algorithm cannot find "a" given only "g", "p" and "ga" mod "p". Such a problem is called the discrete logarithm problem. The computation of "ga" mod "p" is known as modular exponentiation and can be done efficiently even for large numbers.