Hi raduga_fb,
I think you must provide us more details...
If
a can be as big as 256 hex digits, as you said in your first post, using a big integers library and an exhaustive loop, the values which solve your equation
are many and many, as
te$ter pointed out: I calculated
603000 possible solutions for
a in the range
0 - 0x10f1e8fab, using for
c and
b the values you gave!
If numbers are to be manipulated with regular C functions (as
wilson bibe suggested), where the max value for
a can just be 0x7FFFFFFF, then
Code:
c = MOD (a * MOD (a*a, b) , b)
is different from
for
a > 1290 (cube root of 0x7FFFFFFF)!
In any case, the MOD operator is not reversable, in the sense that many inputs can give the same output:
is equivalent to the expression
with n which can assume all integer values...
Best regards
bilbo