How are keys used in encryption algorithms?

Question

I browsed and found good articles about encryption. However, none of them explained why the key length is important and why the key is used. I assume this might work as follows:

Plaintext:   0101001101010101010
Key:         01010010101010010101   //the longer the key, the longer unique sequence
XOR or smth: //result

Is it even a little bit, how does it work, or am I missing something?

Answer 1

Encryption systems are generally much more complex than the XOR system you described. In fact, XORing really only works if you have a key that has at least as many bits as a text message, and you only ever use the key to encrypt a single message. This is called a "one-time keyboard."

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