How to decode an OTP message? First off, I'm extremely sorry if this comes off as a "homework dump", but to clarify, it isn't. I don't want the answer, I want to know how to get to the answer. My cryptography professor gave us an assignment to do, and without explaining this concept, he believes we all understand how to do it, and I definitely don't.

The problem is in two parts:


The one-time pad encryption of the message attack at dawn is 6c73d5240a948c86981bc294814d (the plaintext letters are encoded as 8-bit ASCII and the given ciphertext is written in hexadecimal) What would be the one time pad encryption of the message attack at dusk under the same OTP key? 
The one-time pad encryption of the message attack at dusk is 6c73d5240a948c86981bc294814d (the plaintext letters are encoded as 8-bit ASCII and the given ciphertext is written in hexadecimal) What would be the one time pad encryption of the message attack at noon under the same OTP key?


Thanks for any/all help
If you know the plaintext and the ciphertext, getting the key is trivial.

$$c=m \oplus k$$

Try moving the terms around. Hint: $m$ and $k$ can be functionally swapped (change position with each other), ie. only one term needs to be secret. You already know one term. I've pretty much given you the answer.



About the decoding procedure: The ASCII table linked by Reid is a good resource. Alternatively you can use an online ASCII to Hex encoder to


get the binary representation of the ciphertext
get the binary representation of the known plaintext


and then do the prodecure on paper. Once you understand that you can write a Python script to do the job for you.



only one term needs to be secret: That's what I said above and I'll clarify because that statement is not accurate.

You need to know any 2 terms of the equation $x=a \oplus b$. to solve for any other term. That means $a=x \oplus b$ and of course $x= b \oplus a$. Therefore any stream cipher (or OTP) is secure as long as the adversary only knows one term (namely the ciphertext).