I was just thinking about this and couldn't seem to find anything on it online.
So the idea I had was this:
Generating a random key of some length. Then hashing this key with SHA256 (or something of similar security), then looping through each byte of the hash and each byte of the text and doing an XOR operation with both of these bytes, generating a new byte. Then stringing these new bytes together to create a cipher text. This can be easily reversed if you know the key.
How secure would this potentially be? Other considerations? Advice on improvements to the system?