Is AES block decryption required when using CTR mode?

Question

Cryptography

I'm trying to understand the topic of AES 128 encryption. I implemented the block encryption function, and the function works as it should. I also implemented the block decryption function, and the function, again, works as it should. Then I began to study the modes of connecting blocks. The first glance fell on ECB , implemented it, everything works, the files match, everything is clear and everything is fine. But due to the ECB vulnerability (same blocks are encrypted the same way), I decided to switch to a more secure option, namely CTR . I implemented the CTR and, again, everything works, everything is fine, the files match, but despite this, I am tormented by vague doubts whether it should work this way. The fact is that on the basis of the materials that I studied, it turns out that the regimeCTR does not need the AES block decryption function at all, that is, both encryption and decryption are done using the AES block encryption function. And since decryption of the block is not needed, then the reverse s_box disappears , the methods reverse shift_rows and mix_columns , and much more.

In general, I got to the very question. Did I understand the material I read correctly? Really in CTR mode the AES block decryption function is not needed ? And if so, then how is it that the decryption function is not needed?

Answer 1

Need not. By encryption, you generate the gamma with which you code the data.