I'm trying to follow this example of ElGamal's encryption scheme (page 2, slides 3 & 4), but don't understand this step (decryption, step 2):
$(k^x)^{-1} \pmod m$ Where $k = 10,\ x = 9,\ m = 13$
The slide shows that it becomes $12^{-1} \pmod{13}= 12$
Where did 12 come from? Also, can you help me see how the above equals 12?
I calculate:$12^{-1} = \frac{1}{12}$