Xenocrypt cipher

What the Xenocrypt cipher is

The word is the American Cryptogram Association’s, for a cryptogram in a foreign language, and the Association runs them in many languages. Codebusters uses the Spanish form. The message is a Spanish sentence; each letter is replaced by another under a single alphabet; the word breaks and punctuation stay; and, as in the English versions, no letter stands for itself. Accents are left off, so É is written E, but Ñ is a separate letter in Spanish, which makes the alphabet 27 letters long.

The solver does not need to speak Spanish, though it helps. Spanish text leans heavily on a few letters: E and A are commonly the top two, then O, S, R and N. A one-letter word is usually A, Y, O or E, and never I. Two- and three-letter words are short and frequent: DE, LA, EL, EN, ES, QUE, LOS, LAS, DEL, UNA. Q is followed by U, and words commonly end in a vowel, S or N.

The method is the Aristocrat’s. Tally the letters, try the commonest two as E and A, test the guesses against the short words, and fill the alphabet rows as letters fall. With a K1 alphabet a keyword appears at the start of the plain row, and since Codebusters papers commonly use an English keyword over Spanish text, a familiar English word showing up in the row is the sign the solve is right.

The mistakes are English habits. A student who expects TH, or expects the one-letter word to be I, loses time. Ñ is the other trap: a solver who builds a 26-letter row will be one place off from N onward. And because the message is in Spanish, a nearly finished answer can look wrong to an English reader when it is right; reading it aloud, letter by letter, is a better check than hunting for a familiar word.

How to solve a Xenocrypt cipher

An Aristocrat whose message is in another language, on Codebusters papers usually Spanish. The substitution works as in English: one alphabet throughout, word breaks kept, no letter standing for itself. The Spanish alphabet counts Ñ as its own letter, 27 in all, and accents are left off.

1. Tally the ciphertext. Spanish leans on E and A, then O, S, R and N, so try the commonest two as E and A.
2. A one-letter word is usually A, Y, O or E. It is never I, as it would be in English.
3. Short words narrow it fast: DE, LA, EL, EN, ES, SE, LO and UN among the two-letter words; QUE, LOS, LAS, DEL, UNA and CON among the three.
4. Q is followed by U in Spanish, so a letter that only ever comes before one other letter is a good guess for Q.
5. Fill the alphabet rows as you go. With a K1 keyword, the keyword shows at the start of the plain row and the rest follows in order, with Ñ after N.

A worked example

Decode GQ WEQ GW XRI GWHVGQQI (K1 keyword COMET)

GQ and GW are two-letter words that start alike: EL and ES fit, so G is E.
The rows confirm it:
Plain:  C O M E T A B D F G H I J K L N Ñ P Q R S U V W X Y Z
Cipher: D E F G H I J K L M N Ñ O P Q R S T U V W X Y Z A B C

GQ → EL   WEQ → SOL   GW → ES   XRI → UNA   GWHVGQQI → ESTRELLA

Plaintext: EL SOL ES UNA ESTRELLA
(The sun is a star.)

Xenocrypt in Codebusters

Among the Science Olympiad rule sets OlyPrep has read, the Xenocrypt is on the Division B Codebusters list and not on the elementary lists. The Division B rules OlyPrep has read describe Spanish plaintext under an English K1 keyword alphabet, with at most one Xenocrypt on a regional paper and one or two at state and national level. Scoring follows the paper’s usual rule, by letters, with a decoded message of up to two wrong letters commonly counted as solved.

Teams commonly hand the Xenocrypt to the member with the most Spanish, but the frequency method works without it, and a short list of Spanish function words learned in advance covers most of what a regional message needs. A student who has practised with the Spanish letter frequencies in front of them reads a frequency table faster when a paper provides one.

The lab below draws a sentence from its own Spanish list, builds a K1 alphabet over the 27-letter Spanish alphabet from an English keyword, and keeps the word breaks. The key line prints the keyword and both rows, so a student practising the real thing covers it. The easy, medium and hard settings draw short, medium and long sentences. Check compares letters only and is forgiving about accents and Ñ: an answer typed on an English keyboard as ANO for AÑO is accepted. Reveal shows the plaintext.

Practice the Xenocrypt cipher

The lab below is set to the Xenocrypt cipher alone. Pick a difficulty, generate a challenge, decode it, then check your answer or reveal the solution. It runs in your browser, needs no account, and is unlimited on every OlyPrep plan.

Where the Xenocrypt cipher is tested

The Science Olympiad rule sets OlyPrep has read that name this cipher:

• Science Olympiad Division B — on the Codebusters list, in Spanish under an English keyword

Cipher lists change with each season’s rules; a tournament’s own rulebook is the authority on what it tests.