1. I feel like I have a very superficial understanding of shift ciphers and how they relate to modular arithmetic. I don't understand how they found the multiplicative inverse for 9(mod26) is 3. Are there multiple multiplicative inverses? I also don't completely understand how you can have a function or an encryption that is not one to one. Why do we need to make sure that the gcd(z,26)=1?
2. I think it is pretty amazing that you can make a cipher text so hard to break if the adversary only has the cipher text available. But then again, if you just know a little bit of plaintext with the cipher text, depending on the cipher, description becomes so much easier so suddenly. I still don't understand the Affine Ciphers completely, but I would like to know why they are so much more secure. I would like to continue practicing decrypting substitution ciphers since it uses so much wit and cleverness.
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