ACA and YOU: Chapter 5

How to encipher a problem for The Cryptogram

The Cryptogram depends on you for problems published for the pleasure of all. Make a note of interesting plaintext as you read. Polish you language skills and gain new insights by enciphering. Then send the results to the department Editors so others may pit their skills against your challenge!

No game is entertaining unless players are assured a square deal. Thus to insure justice and to maintain high standards guidelines have been worked out over the years. All are subject to editorial judgment in individual cases. A contribution which meets the standards will always be more welcome than one which does not.

The departments give varied fare for experts and beginners. Your contribution will be tested by the department Editor, and graded for difficulty. If you have not already done so, a suitable tip and title will be added.

Please use a separate sheet of paper for each encipherment, write on one side of the paper only, and use the format employed for that cipher in "The Cryptogram". You should show your working of the solution on a separate page.

We hope all members will contribute generously and regularly so the Editor's "bins" (files) will be kept full. Remember also a published "con" can be counted as a "sol"; see Chapter 4 for details.

Enciphering Guides

  1. Text must make sense. Check word meanings to avoid impossibilities and contradictions. Telegraphic text, incomplete sentences without verbs, or mere lists of words are not acceptable.
  2. Definite and indefinite articles may be omitted, but for Aristocrats, punctuation must be correct. Numerals are to be written out in full (except for 6x6 Bifids).
  3. Misspelling, mixed cases, wrong tenses, or other grammatical errors must be avoided. Check and recheck if in doubt.
  4. Text worth reading should be the solvers' reward. Unfair tactics reduce the value of the challenge; cleverness is the essence of a tough problem. Find what features of the cipher aid in its decipherment, and see if you can obscure these features suitably.
  5. Follow the guidelines in this book for proper lengths for ciphers. Good problems may have to be discarded because of excessive length, but don't spoil a poem for the sake of a few letters!
  6. Unfair text contains words not listed in standard dictionaries with the exception of proper nouns and popular slang. Obsolete words, reformed spellings, and foreign words are unacceptable.
  7. In Xenocrypts, simple language is preferred to technical quotations. Accents may be omitted. In simple substitutions, use a keyword to aid in deciphering irregular verbs, singletons, etc. (K2s are preferred; K4s and random alphabets must not be used).

    Keys may be in English or the foreign language, but should be chosen to assist the decipherment. Study what other encipherers do.

  8. In Simple Substitutions, use only capital letters. No letter may stand for itself. Add an asterisk to the left of any proper noun in an Aristocrat, Keyphrase, or Ragaby, and any Xenocrypts of these types. (In Xenos an asterisk is also used in the tip to denote a letter or group of letters that does not actually appear. That is, it may be used to denote one or more letters missing in the alphabet, the square, or in the text.)
  9. In Periodics, the ciphertext should be submitted in blocks of five letters.
  10. In Cryptarithms, use no base under 8 or over 16. Bases 10, 11, 12, and 16 are preferred. Root extractions are limited to square and cube roots. There must be only one possible solution to a Cryptarithm. Check, for instance, that any letters occurring once only are not in the same column.

The Question of Original Systems

So you have the perfect indecipherable system? Perhaps you have heard that the ACA is a proving ground for such things? Stop! No practicable cipher system has been invented which is unbreakable by experts provided they have sufficient material to work on, except those sophisticated machine and computer ciphers which are outside the range of hobby cryptography.....and even these have yielded.

For over 400 years, cryptographers have been writing on the subject seriously. Systems once thought to be unbreakable have succumbed to analysis. Without a thorough knowledge of what has been done, and of what makes a good system, the chances of inventing a new one are slim. Variations are endless and too often worthless.

Below is a list of guidelines for a successful military cipher. Variations for diplomatic and commercial use are minor, but in any case the ciphers are intended for heavy traffic use with difficulty of solution appropriate to the timeliness of the enciphered message. Few cryptographers are able to judge the weak spots of a system, even one that seems to meet the requirements. If you do invent a new one, let it sit for a while and "digest" in your mind whilst you try and find a similar system already in use, or in use in the past.

Note that we already use some 60 ciphers in "The Cryptogram". To be considered seriously, you would first have to describe your new cipher in an explanatory article. Based on this, and your own record of ability in cryptography, the system might be considered for acceptance for regular use if the reaction of the membership was favorable.

The criteria for a suitable military cipher are:

  1. The cipher must be suitable for telegraphic transmission, with no special symbols.
  2. Ciphertext should not be much longer than the plaintext for rapidity in encipherment, transmission, and legitimate decipherment.
  3. Security must not depend on any limitations of plaintext.
  4. Decipherment must yield unambiguous plaintext; one possible message.
  5. Necessary apparatus must be small enough to be easily carried.
  6. Methods of encipherment and decipherment must be simple, requiring few operations and putting little mental strain on the operator.
  7. Errors being inevitable, omission or error in a letter or group should not affect the rest for the text. Rapid and easy correction must be possible.
  8. Text comparisons of several cipher messages with a fragment of plaintext, or with the text of another cipher, should not lead to a "break".
  9. The interceptor is assumed to possess all details of the system but the keyword. An unalterable system, or one with few variations, is poor. The key must be easily altered, easily remembered, land vastly variable.

Finally, while we were once the proud reservoir of cryptographic talent for our country, "paper and pencil" work is now rarely important in professional work. In considering new systems for presentation to the ACA, we give more weight to the cryptographic interest, subjectively judged, than to adherence to any specific requirements. Experience must still back any invention, for only through solving can you come to judge the degree of interest your own invention might generate among fellow members.