Is XOR in a CBC-like mode secure?

Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively.

The first byte of ciphertext is computed like this:

$C_{1} = K_{1} \oplus P_{1}$

And the rest of the bytes are computed like this:

$C_{i} = K_{i} \oplus P_{i} \oplus P_{i-1}$

Is this a good way of encrypting data, or is there some loophole that I've overlooked?

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 Hello, welcome to crypto; I edited your title to be a little more descriptive (I realise you probably didn't know what to put as the title :)) - if you want to improve it, or roll it back, there is an edit link directly underneath your question which you can use at any time :) – Antony Vennard May 12 '12 at 19:59 Thanks, Ninefingers! You're right, I had no idea what to put as the title. – Jack V. May 12 '12 at 20:27 One could name this mode PBC (plaintext block chaining). But as each block gets encrypted with a different key, this isn't really a block cipher mode. – Paŭlo Ebermann♦ May 12 '12 at 22:31