Can I decode a message that was encrypted with a one-time pad if I have the key used to encrypt it? If so, how?
Yes, you can.
The one-time pad is usually employed as a symmetric encryption, i.e., encryption key and decryption key are the same. It is often as simple as applying
XOR of key and message.
Note that the one-time pad suffers from some problems:
- You can use a key exactly one time, otherwise the encryption is broken
- There is no protection against altering the encrypted message
- You need a way to exchange the one time pad keys in a secure way.