# Number of bit operations required for encryption in a Block cipher

I want to find out how many bit operations are performed for encryption in AES-128 with messages size $$128$$ bits.

For public key encryptions such as RSA and ElGamal, I know that number of bit operations required are $$O(n^3)$$ if the key considered has $$n$$ bits.

Are these equal to $$O(1)$$?

• This question has been asked before. No, we don't use Big-Oh for symmetric ciphers, And that really depends on the implementation, use of a pre-computed table or not, etc. The only article that really counted is TOA et. al They went on this to show that their attack better than the brute-force. Mar 4, 2021 at 17:14
• And, for the RSA, Why it is $O(n^3)$? Mar 4, 2021 at 17:17
• RSA involves modular exponentiation. So, if we use square and multiply algorithm, then it is so. It can further be optimized.
– PAMG
Mar 4, 2021 at 17:20
• It is $\mathcal{O}(3\cdot n^2)$ at most whem $e=3$ Mar 4, 2021 at 17:23
• But e is not 3, in general. What if I want to send a same messages to more than 3 entities?
– PAMG
Mar 5, 2021 at 16:39