I've been reading a bit recently on constructed languages like Esperanto. I came across one that developed out of something called "LOGLAN" that was published in Scientific American in the early sixties. The current active project is called "Lojban". It has one really curious property that gave me an idea for an interesting symmetric-key cryptosystem. All "native" Lojban words are of entirely predictable forms. "Root" words are all five characters containing three consonants and two vowels in one of two patters (CCVCV and CVCCV). "Structure" words have four forms (VV, CV, CVV, and CV'V). "Combining forms" have two forms (CVC and CV'C). All other words are not "native" words (being either proper names or borrowed words). The upshot of this is that there is a fixed limit on the size of the Lojban dictionary of 249500 words (given 17 consonants and five vowels). The grammar of the language is *so* regularized that they are able to give a YACC description for it. A message written entirely using native Lojban words can be encrypted in a codebook fashion where the particular codebook to be used is a permutation of the dictionary represented by an 40-bit number (18 bits to permut the "root word" list, 10 bits for the "structure word" list, and 12 bits for the "combining form" list). This system has the interesting property that *any* plaintext with the same grammatical structure is a potential encryption of a given cyphertext. This is similar to some more usual cryptosystems which operate at the lexical level but which are designed to create this effect, but has the curious side effect that it is *very* easy to determine a false-key which makes the transmitted message say nearly anything you want, thus making mandatory key escrow systems irrelevant. When you want to send the message "attack at dawn", you devise a grammatically identical message, "party 'til you puke" (which is grammatically identical in Lojban), generate a random key, as well as the key representing a similar permutation, but with "attack" and "party" exchanged, "puke" and "morning" exchanged, and so forth. Transmit the message with the false key in the LEAF field (or report it to your government-approved escrow agency) and government eavesdroppers get the wrong message. Other eavesdroppers get a grammatically correct, but apparrently nonsensical message ("drink by brick"). There's still the problem of borrowed words and proper names, which remain problems in any codebook approach, but represents a small portion of the language, and the words which represent individual letters are part of the "structure words" category, and could be sent spelled-out. This works well in Lojban because it never changes word forms based on grammatical usage. Most natural language declensions and conjugations would make the encrypted message ungrammatical, and make it *much* more difficult to determine a false key for the LEAF field. The irregularity of word forms makes the dictionary much more complicated, too. Comments?