How perfect is Voynichese?

[Mauro]

Uh, no, not even close. A one-time pad is theorethically perfect, it's way harder to decrypt even than, say, RSA encryption.

For a letter-size document, perhaps.  A book-size text in codebook cipher can be cracked by guessing the most common words and using external clues (topic, illustrations, recurring formulas, partially leaked plaintext...) 

The Rohonc codex seems to be an example of a "codebook" cipher (and even in an orignal language) that was cracked this way.

All the best, --stolfi

A You are not allowed to view links. Register or Login to view. is not a codebook cipher. The resulting encrypted text is a random string and gives zero informations to an attacker.

The resulting ciphertext is impossible to decrypt or break if the following four conditions are met:

The key must be at least as long as the plaintext.
The key must be truly random.
The key must never be reused in whole or in part.
The key must be kept completely secret by the communicating parties.
These requirements make the OTP the only known encryption system that is mathematically proven to be unbreakable under the principles of information theory.