As David Kahn and others have noted, the encrypted texts that have survived from the European Middle Ages do tend to be, as ciphers, simple: vocalic substitution ciphers, for example, or the dot or number ciphers described by both Isidore of Seville and Rabanus Maurus. For all that the basic mechanism of these substitution ciphers is simple, even "simple in the extreme", however, a surprising number of these texts do not resolve cleanly into plaintext. This chapter considers two of these problematic ciphers and their contexts: the cipher on the right hand panel of the Franks Casket, and the interpolated cipher in Exeter Book Riddle #36. The casket's images depict, wildly, episodes from Germanic mythological history, Christian narratives, and Roman mythology and history. The fact of the existence of the cipher alone charges the way we approach the rest of the casket's images and texts.