Cryptanalysis of the "Kindle" Cipher

In this paper we study a 128-bit-key cipher called PC1 which is used as part of the DRM system of the Amazon Kindle e-book reader. This is the first academic cryptanalysis of this cipher and it shows that PC1 is a very weak stream cipher, and can be practically broken in a known-plaintext and even in a ciphertext-only scenario. A hash function based on this cipher has also been proposed and is implemented in the binary editor WinHex. We show that this hash function is also vulnerable to a practical attack, which can produce meaningful collisions or second pre-images.