I have RSA d (private exponent) that is 0x10001 and n (modulus).
As I understand, n is common between Private and Public keys.
Now I need to calculate e (public exponent), is it possible?
I also tried Yafu, but no result..
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You seem to assume that you have the private key – but you don’t. And thus, what you’re asking isn’t possible.
First, I’m willing to bet that your 0x10001 is actually the public exponent e and not the private exponent d, just judging from experience. And if you’re “decrypting” with it, that just sounds like you’re using the public key to verify a signature.
But it doesn’t matter, from a mathematical perspective those are one and the same. d and e are each other’s exponential inverse modulo n, so if you could get e from d, then the same process could be applied to get d from e, which would break RSA.
The only known and computationally feasible way to compute the exponential inverse of a number modulo n = p*q is to find its multiplicative inverse modulo λ(n) = lcm(p-1, q-1)… which requires you to know p and q.