In (ℤ/nℤ)*, the discrete log of b to base g is an exponent x with g^x ≡ b (mod n). Computing it is believed to be hard (basis for Diffie–Hellman and similar crypto).. The key formula is x such that g^x ≡ b (mod n). This concept is typically introduced in College. Understanding this concept builds a strong foundation for more advanced mathematics.