To distinguish the two, we refer to (5) as decipherment, rather than decoding.
during decipherment, our goal is to estimate the channel model parameters θ. Re-writing Equations 3 and 4 for word substitution decipherment, we get: Challenges: Unlike letter substitution ciphers (having only 26 plaintext letters), here we have to deal with large-scale vocabularies (10k-1M word types) and corpora sizes (100k cipher tokens).