XORing to detect decrypted value? So I am doing a CTF and I have found a text that is full with hexadecimal encrypted value with XOR (that was a given hint from the previous flag). I don't have the key but I know the length of the key is $8$. I also know that the word Congratulations is in the file somewhere. So, I guessed that if I XORed Congratu with the first 16 hex bytes assuming that I'll recover the key as a result to fully decrypt the message but that didn't seem to give me a correct result. I'm guessing that Congratulations may not be the first, which is why I'm having this issue. Is there anything that you guys recommend to solve this quickly?
It sounds like a basic Vigenere cipher. From what you wrote, you even have some knowledge about the plaintext, but don't know the position.

You only tried out the first position, maybe just try this with shifting the worst to another position? Or just break the Vigenere cipher as if you knew only the keylength.