Wahrig Wissenschaftslexikon Chondroblastom - wissenschaft.de
Anzeige
Anzeige

Wahrig Wissenschaftslexikon

Chondroblastom

♦ Chon|dro|blas|tom  〈[çn–] n. 11; Med.〉 Knorpelgeschwulst; Sy Chondrom [<grch. chondros ”Knorpel“ + Blastom]

♦ Die Buchstabenfolge chon|dr… kann in Fremdwörtern auch chond|r… getrennt werden.
Anzeige

bild der wissenschaft | Aktuelles Heft

Anzeige

Dossiers

Aktueller Buchtipp

Sonderpublikation in Zusammenarbeit  mit der Baden-Württemberg Stiftung
Jetzt ist morgen
Wie Forscher aus dem Südwesten die digitale Zukunft gestalten

Wissenschaftslexikon

The homophonic Polybius is a simple but hard to break manual cipher. Can a reader break a message I have encrypted in this scheme?

Designing a purely manual cipher (i.e., one that can be executed without a computer, cipher machine, or cipher tool) has proven a difficult problem. Most designs are either too complicated for practical use or insecure (some are even both). Almost all manual ciphers that were developed in the pre-computer era can today be broken with a computer program.

Anzeige

Although manual encryption algorithms lost importance with the advent of computer technology, they are still an active field of research.

 

Homophonic Polybius

Today, I’m going to present a manual cipher I call “homophonic Polybius”. It is based on the Polybius cipher, a system invented by the old Greeks, and enhanced by the use of homophones. I have never seen this system in the literature, but I can imagine that similar concepts have been used before.

The homophonic Polybius is simple, but might be hard to break. It replaces every letter of the plaintext with a letter pair (digraph), which means that the ciphertext is double as long as the plaintext. Such a property is not desirable, but can be tolerated if one is dealing with a plaintext of only a few hundred letters or less.

In the following, we work with a 25-letter alphabet. There is no Q. If a Q appears in the plaintext, we take a K instead.

For the homophonic Polybius cipher we need two keywords. As an example, we take PASTA and NOODLE. Each keyword is used to rearrange the alphabet in the following way: Write the keyword first, omit repeating letters, append the remaining letters. For PASTA we receive:

PASTBCDEFGHIJKLMNORUVWXYZ

With NOODLE, the alphabet is written as follows:

NODLEABCFGHIJKMPRSTUVWXYZ

Now we construct a substitution table. In the first step, we write the PASTA alphabet as follows (three lines on the top, two columns on the left):

In the second step, the NOODLE alphabet is added as a five-by-five square:

With this Polybius-type substitution table, we have several options to encode each letter. For instance, the A can be encrypted as OP, OC, OH, RP, RC, or RH. In other words: We have six homophones for each letter of the alphabet. Let’s now encrypt the plaintext TO BE OR NOT TO BE:

T  O  B  E  O  R  N  O  T  T  O  B  E  X XK ND OI ML ND WA MH MI WF XF MA RI NB ZJ

The ciphertext is: XK ND OI ML ND WA MH MI WF XF MA RI NB ZJ

Each letter pair in the ciphertext was randomly chosen from the six homophones available for the respective letter. For instance, the T at the beginning was encrypted as XK, but could also have been encoded as WT, WF, WK, XT, or XF. When using this scheme, one should switch between the homophones of a certain letter in a non-regular way.

 

A challenge

The following ciphertext has been encrypted in a homophonic Polybius cipher:

MG VI VH PG JG KE KB KB VR LU JG ZG JE VN ZD VC KA ME TB VR JS TU PG KA JS
VX VB VH PE KE VS KB PB KA MA PF ZX KA MB PA ME PI VE KI VF KB VA PD MG ZC
VB KU KS VH PE KA VC YX VE KA TS TC KA VB KI KE VB ME PR MA KH KB VC TI TU
PG KA VB VF ZF VH PE KG VN KB PC KA ME PX ZR KA MD PE MG PI VG KU VR KN VD
VR MU MG VS KG KH PF PE VU KE JA KN JN VF VH PE JA VB KN PD KG ME PR ZR KG
VI KG MG PI VD PG MG ZG KG ZB VR KN VD KU MR VU ZD VF MU VU PE KG KE KI PR
PG VU ZD VB ZF VG KG VB VD KG VN KI KE VD VG PD MG ZD KE KD VD KU KB MC KG
KB KI KN KA TI KG KA KS PG ZR KN KD VB KG KD MG KB KD MI KU LI VH KG KE KB

The plaintext is in English, consisting of 200 letters. Both keywords are misspelled expressions, which means that a dictionary attack won’t work. Can a reader solve this challenge?


Further reading: Solve the Bigram 600 challenge and set a new world record

ver|fei|nern  〈V. t.; hat〉 feiner machen, verbessern ● den Geschmack einer Speise ~; seinen Geschmack ~; die Technik der Mannschaft hat sich im Lauf der Zeit verfeinert; eine Soße, Suppe mit Sahne ~

Bau|leit|pla|nung  〈f. 20〉 auf der Grundlage des Baugesetzbuches (BauGB) festgelegte Planung der städtebaulichen Nutzung u. Entwicklung von Grundflächen einer Gemeinde, umfasst in der ersten Stufe die Aufstellung eines Flächennutzungsplan und in der zweiten Stufe die Aufstellung von Bebauungsplänen für Teilbereiche der gemeindlichen Flächen

» im Lexikon stöbern
Anzeige
Anzeige