RC4 was an encryption method briefly in vogue for its speed and simplicity. Anyone who designs or implements cryptography will know that those are two words that, while good when applied with other words, such as secure, thoroughly tested, and 300 rounds, are not great when they make up the core of a description.
PTis your plaintext value
Keyis the secret value set to encrypt the values
CTis the encrypted cipher text
exclusive or or
bitwise addition, which is where two values are broken down into binary, overlayed, and where the numbers match, a
0 is returned, and where the numbers don't match, a
1 is given.