I started learning cryptography. I have learned some basic stuff. I'm also learning about information security, so I was wondering how do hackers use cryptography for bypassing antivirus software? I don't have some deep understanding on how Antivirus software works but I know that every Antivirus has base of signatures, so when we scan exe file it actually compares signature of exe with signatures in it's own base, and if it matches, Antivirus will identify exe as malware. So by applying some cryptographic algorithm on exe file (using tool "Crypter"), they change signature of exe, so antivirus can't detect it as malware, right? But concretely, how do they apply cryptograpyic algorithm on exe file? I saw only in my book how plaintext is crypted. There is no information about crypting exe files there (or I didn't see it). I use book "Applied Cryptography, Bruce Schneier". Maybe this was stupid question but don't blame me, I'm amateur :) If there is some book covering this matter, please suggest it to me, I will be grateful. Thanks in advance

I was wondering how do hackers use cryptography for bypassing antivirus software.

I don't have some deep understanding on how antivirus software works, but I know that every antivirus has base of signatures, so when we scan .exe file it actually compares signature of .exe with signatures in it's own base, and if it matches, antivirus will identify .exe as virus. 

So by applying some cryptographic algorithm on .exe file (using tool "Crypter"), they change signature of .exe, so antivirus can't detect it as malware, right? But concretely, how do they apply cryptograpyic algorithm on .exe file? I saw only in my book how plaintext is crypted.