C语言XOR加密代码特定行逻辑疑问及适配性咨询

Hey there! Let's break this down clearly since you're new to C and trying to wrap your head around this XOR encryption code.

First, let's look directly at the line you're confused about in the else block:

msg[ind] = (_len>0?buf[ind-24]:'@')^msg[ind-24];

你的猜测是否正确？ #

Nope, your guess isn't right. The code isn't XORing with an index offset by -12—it's using an offset of -24. Let's split this expression into parts to make it clearer:

• The ternary operator (_len>0?buf[ind-24]:'@'):
  • When _len is still greater than 0, it takes the element from the buf array at position ind-24 (since ind is at least 24 here, this is a valid index into buf).
  • When _len drops to 0 or below (meaning we've processed all elements in buf), it uses the character '@' (ASCII value 64) as a filler.
• This value is then XORed with the element in the msg array at position ind-24, and the result is stored in msg[ind].

Quick walkthrough of the full loop logic #

To give you context, here's what the whole loop is doing:

• _len starts as len + 24, so we're processing the original buf content plus an extra 24 positions.
• The loop runs as long as either _len > 0 (we still have buf elements to process) or count % 24 != 0 (we need to pad the output to a multiple of 24 bytes).
  • When ind < 24: We copy the first 24 elements from the bytes array into msg—this acts like an initial seed for the encryption.
  • When ind >= 24: We generate each new msg element using the XOR logic we just broke down, reusing the earlier msg values (24 positions back) combined with buf data or the '@' filler.

Does this code fit Figure1's requirements? #

Unfortunately, without knowing what Figure1 specifies (like the required encryption mode, key rules, input/output format, or padding requirements), I can't say for sure if this code matches its needs. If you can share details about what Figure1 expects (e.g., is it a specific XOR stream cipher, does it require a certain block size, etc.), we could verify this more precisely.

内容的提问来源于stack exchange，提问作者Jinwoo Bae