210:
232:) with the letters of the keyword (dropping any duplicate letters), then fill the remaining spaces with the rest of the letters of the alphabet in order (usually omitting "J" or "Q" to reduce the alphabet to fit; other versions put both "I" and "J" in the same space). The key can be written in the top rows of the table, from left to right, or in some other pattern, such as a spiral beginning in the upper-left-hand corner and ending in the center. The keyword together with the conventions for filling in the 5 by 5 table constitute the cipher key.
281:
265:(opposite) of the two shift rules, selecting the letter to the left or upwards as appropriate. The last rule remains unchanged, as the transformation switches the selected letters of the rectangle to the opposite diagonal, and a repeat of the transformation returns the selection to its original state. The first rule can only be reversed by dropping any extra instances of the chosen insert letter — generally "X"s or "Q"s — that do not make sense in the final message when finished.
1919:
386:
346:
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322:
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298:
523:
chart). If the new square is deemed to be an improvement, then it is adopted and then further mutated to find an even better candidate. Eventually, the plaintext or something very close is found to achieve a maximal score by whatever grading method is chosen. This is obviously beyond the range of typical human patience, but computers can adopt this algorithm to crack
Playfair ciphers with a relatively small amount of text.
551:. In this story, a Playfair message is demonstrated to be cryptographically weak, as the detective is able to solve for the entire key making only a few guesses as to the formatting of the message (in this case, that the message starts with the name of a city and then a date). Sayers' book includes a detailed description of the mechanics of Playfair encryption, as well as a step-by-step account of manual cryptanalysis.
101:
27:
558:
cipher as a medium-grade cipher in WWII, based on the
British Playfair cipher they had broken early in WWI. They adapted it by introducing a second square from which the second letter of each bigram was selected, and dispensed with the keyword, placing the letters in random order. But with the German
526:
Another aspect of
Playfair that separates it from four-square and two-square ciphers is the fact that it will never contain a double-letter digram, e.g. EE. If there are no double letter digrams in the ciphertext and the length of the message is long enough to make this statistically significant, it
130:
when it was developed because of its perceived complexity. Wheatstone offered to demonstrate that three out of four boys in a nearby school could learn to use it in 15 minutes, but the Under
Secretary of the Foreign Office responded, "That is very possible, but you could never teach it to attachés."
91:
used for simple substitution ciphers does not work with it. The frequency analysis of bigrams is possible, but considerably more difficult. With 600 possible bigrams rather than the 26 possible monograms (single symbols, usually letters in this context), a considerably larger cipher text is required
599:
Use of the
Playfair cipher is generally explained as part of the preamble to the crossword. This levels the playing field for those solvers who have not come across the cipher previously. But the way the cipher is used is always the same. The 25-letter alphabet used always contains Q and has I and J
514:
ciphers, though the relative simplicity of the
Playfair system makes identifying candidate plaintext strings easier. Most notably, a Playfair digraph and its reverse (e.g. AB and BA) will decrypt to the same letter pattern in the plaintext (e.g. RE and ER). In English, there are many words which
515:
contain these reversed digraphs such as REceivER and DEpartED. Identifying nearby reversed digraphs in the ciphertext and matching the pattern to a list of known plaintext words containing the pattern is an easy way to generate possible plaintext strings with which to begin constructing the key.
522:
method. This starts with a random square of letters. Then minor changes are introduced (i.e. switching letters, rows, or reflecting the entire square) to see if the candidate plaintext is more like standard plaintext than before the change (perhaps by comparing the digrams to a known frequency
235:
To encrypt a message, one would break the message into digrams (groups of 2 letters) such that, for example, "HelloWorld" becomes "HE LL OW OR LD". These digrams will be substituted using the key table. Since encryption requires pairs of letters, messages with an odd number of characters usually
595:
The cipher lends itself well to crossword puzzles, because the plaintext is found by solving one set of clues, while the ciphertext is found by solving others. Solvers can then construct the key table by pairing the digrams (it is sometimes possible to guess the keyword, but never necessary).
252:
If the letters are not on the same row or column, replace them with the letters on the same row respectively but at the other pair of corners of the rectangle defined by the original pair. The order is important – the first letter of the encrypted pair is the one that lies on the same
236:
append an uncommon letter, such as "X", to complete the final digram. The two letters of the digram are considered opposite corners of a rectangle in the key table. To perform the substitution, apply the following 4 rules, in order, to each pair of letters in the plaintext:
146:. This was because Playfair is reasonably fast to use and requires no special equipment - just a pencil and some paper. A typical scenario for Playfair use was to protect important but non-critical secrets during actual combat e.g. the fact that an artillery barrage of
567:. Messages were preceded by a sequential number, and numbers were spelled out. As the German numbers 1 (eins) to twelve (zwölf) contain all but eight of the letters in the Double Playfair squares, pro forma traffic was relatively easy to break (Smith, page 74-75)
150:
would commence within 30 minutes to cover soldiers' advance towards the next objective. By the time enemy cryptanalysts could decode such messages hours later, such information would be useless to them because it was no longer relevant.
240:
If both letters are the same (or only one letter is left), add an "X" after the first letter. Encrypt the new pair and continue. Some variants of
Playfair use "Q" instead of "X", but any letter, itself uncommon as a repeated pair, will
502:
of the cipher involves searching through the key space for matches between the frequency of occurrence of digrams (pairs of letters) and the known frequency of occurrence of digrams in the assumed language of the original message.
244:
If the letters appear on the same row of your table, replace them with the letters to their immediate right respectively (wrapping around to the left side of the row if a letter in the original pair was on the right side of the
248:
If the letters appear on the same column of your table, replace them with the letters immediately below respectively (wrapping around to the top side of the column if a letter in the original pair was on the bottom side of the
286:
The first step of encrypting the message "hide the gold in the tree stump" is to convert it to the pairs of letters "HI DE TH EG OL DI NT HE TR EX ES TU MP" (with the null "X" used to separate the repeated "E"s). Then:
30:
The
Playfair cipher uses a 5Ă—5 grid of letters, and encrypts a message by breaking the text into pairs of letters and swapping them according to their positions in a rectangle within that grid: "HI" becomes
592:) occasionally incorporate Playfair ciphers. Normally between four and six answers have to be entered into the grid in code, and the Playfair keyphrase is thematically significant to the final solution.
415:
Thus the message "hide the gold in the tree stump" becomes "BM OD ZB XD NA BE KU DM UI XM MO UV IF", which may be restructured as "BMODZ BXDNA BEKUD MUIXM MOUVI F" for ease of reading the cipher text.
186:
Playfair is no longer used by military forces because of known insecurities and of the advent of automated encryption devices. This cipher is regarded as insecure since before
939:
123:, first Baron Playfair of St. Andrews, who promoted its use. The first recorded description of the Playfair cipher was in a document signed by Wheatstone on 26 March 1854.
1899:
1729:
490:
Like most classical ciphers, the
Playfair cipher can be easily cracked if there is enough text. Obtaining the key is relatively straightforward if both
1156:
718:
530:
A good tutorial on reconstructing the key for a
Playfair cipher can be found in chapter 7, "Solution to Polygraphic Substitution Systems," of
1582:
1101:
534:, produced by the United States Army. Another cryptanalysis of a Playfair cipher can be found in Chapter XXI of Helen Fouché Gaines'
873:
794:
276:
Using "playfair example" as the key (assuming that I and J are interchangeable), the table becomes (omitted letters in red):
1149:
225:. Memorization of the keyword and 4 simple rules was all that was required to create the 5 by 5 table and use the cipher.
1081:
774:
637:
1575:
1066:
1049:
709:
No duplicate letters are allowed, and one letter is omitted (Q) or combined (I/J), so the calculation is 600 = 25Ă—24.
1372:
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1142:
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1116:
1111:
1568:
580:
519:
1952:
1894:
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1947:
1773:
767:
The Codebreakers: The comprehensive history of secret communi cation from ancient times to the internet
147:
1074:
The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet
193:
The first published solution of the Playfair cipher was described in a 19-page pamphlet by Lieutenant
1889:
209:
155:
994:
Currer-Briggs, Noel (1987). "Some of ultra's poor relations in Algeria, Tunisia, Sicily and Italy".
1879:
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55:
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48:
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175:
20:
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8:
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1452:
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941:
American Army Field Codes In the American Expeditionary Forces During The First World War
935:
194:
111:
Playfair cipher was the first cipher to encrypt pairs of letters in cryptologic history.
87:
systems then in use. The Playfair cipher is thus significantly harder to break since the
80:
26:
1753:
1737:
1684:
1519:
1438:
1344:
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507:
228:
To generate the key table, one would first fill in the spaces in the table (a modified
222:
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112:
88:
59:
1207:
84:
1813:
1803:
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616:
542:
511:
1748:
1165:
1003:
917:
881:
832:
Memoirs and Correspondence of Lyon Playfair: First Lord Playfair of St. Andrews ...
805:
676:
664:, a clue to solving the Morningstarr cipher is encrypted using the Playfair cipher.
632:
conceals the formula for a new high-strength metal alloy using the Playfair cipher.
611:
547:
198:
1038:
1309:
1235:
1217:
830:
555:
229:
163:
135:
1823:
1743:
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1423:
1304:
1197:
1192:
564:
1106:
1007:
667:
The Playfair cipher serves as a plot device in a season 2 episode of the 2019
385:
345:
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321:
309:
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1941:
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120:
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63:
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1854:
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423:
Assume one wants to encrypt the digram OR. There are five general cases:
1833:
1498:
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1329:
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187:
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134:
It was however later used for tactical purposes by British forces in the
1102:
Extract from some lecture notes on ciphers – Digraphic Ciphers: Playfair
381:
10. The pair EX (X inserted to split EE) is in a row, replace it with XM
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1763:
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1719:
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1514:
1319:
1250:
661:
495:
116:
51:
1783:
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588:
560:
491:
541:
A detailed cryptanalysis of Playfair is undertaken in chapter 28 of
268:
There are several minor variations of the original Playfair cipher.
1828:
1788:
1240:
861:"A History of Communications Security in New Zealand By Eric Mogon"
619:
gives a blow-by-blow account of the cracking of a Playfair cipher.
680:, a Playfair cipher is discovered in the footnotes of the story.
100:
1709:
1433:
1299:
1173:
142:
and for the same purpose by the British and Australians during
71:
653:, a Playfair cipher clue is used to send Anja Creed to Venice.
1403:
1398:
1339:
723:(1996) David Kahn, Scribner Books from Simon & Schuster
586:(published in the Saturday edition of the British newspaper
527:
is very likely that the method of encryption is Playfair.
518:
A different approach to tackling a Playfair cipher is the
498:
are known. When only the ciphertext is known, brute force
425:
1097:
Online encrypting and decrypting Playfair with JavaScript
201:
described it in 1942 as providing very little security.
641:, a treasure hunt clue is encoded as a Playfair cipher.
600:
coinciding. The key table is always filled row by row.
1730:
Cryptographically secure pseudorandom number generator
1122:
Python and streamlit implementation of Playfair cipher
1040:
Cryptanalysis / a study of ciphers and their solutions
924:. Fort Leavenwoth, Kansas: Army Service Schools Press.
536:
Cryptanalysis / a study of ciphers and their solutions
407:
13. The pair MP forms a rectangle, replace it with IF
393:
11. The pair ES forms a rectangle, replace it with MO
1126:
922:
An Advanced Problem in Cryptography and Its Solution
374:
9. The pair TR forms a rectangle, replace it with UI
367:
8. The pair HE forms a rectangle, replace it with DM
360:
7. The pair NT forms a rectangle, replace it with KU
353:
6. The pair DI forms a rectangle, replace it with BE
341:
5. The pair OL forms a rectangle, replace it with NA
329:
4. The pair EG forms a rectangle, replace it with XD
317:
3. The pair TH forms a rectangle, replace it with ZB
293:
1. The pair HI forms a rectangle, replace it with BM
221:
The Playfair cipher uses a 5 * 5 table containing a
993:
1037:
475:* * * * * * * R * * * * O * * * * I * * * * * * *
464:* * * * * * * * * * * O R W * * * * * * * * * * *
453:Z * * O * * * * * * * * * * * R * * X * * * * * *
442:* * O * * * * B * * * * * * * * * R * * * * Y * *
431:* * * * * * O Y R Z * * * * * * * * * * * * * * *
305:2. The pair DE is in a column, replace it with OD
1939:
1117:Javascript implementation of the Playfair cipher
1112:Cross platform implementation of Playfair cipher
506:Cryptanalysis of Playfair is similar to that of
742:Northern Kentucky University, Chris Christensen
554:The German Army, Air Force and Police used the
400:12. The pair TU is in a row, replace it with UV
79:), instead of single letters as in the simple
1576:
1150:
1059:Station X: The Codebreakers of Bletchley Park
906:. Open Road Media. Kindle Edition. p. 6.
850:. Open Road Media. Kindle Edition. p. 6.
418:
802:Appalachian State University, Dr. Rick Klima
904:Lonely Vigil: Coastwatchers of the Solomons
874:"The History of Information Assurance (IA)"
848:Lonely Vigil: Coastwatchers of the Solomons
732:
570:
58:cipher. The scheme was invented in 1854 by
1583:
1569:
1164:
1157:
1143:
1061:(1998, Channel 4 Books/Macmillan, London)
660:(part three of a trilogy for children) by
384:
344:
332:
320:
308:
296:
279:
257:as the first letter of the plaintext pair.
916:
878:Government Communications Security Bureau
69:The technique encrypts pairs of letters (
934:
880:. New Zealand Government. Archived from
835:Harper & Brothers. pp. 158–159.
208:
119:, but it carries the name of his friend
99:
25:
1940:
1035:
981:
969:
957:
1564:
1138:
792:
603:
1071:
901:
845:
828:
788:
786:
764:
760:
758:
213:The Playfair system was invented by
178:Intelligence also used this cipher.
54:technique and was the first literal
987:
795:"Secret Codes Through World War II"
115:invented the cipher for secrecy in
13:
996:Intelligence and National Security
638:National Treasure: Book of Secrets
14:
1964:
1090:
947:. U.S. War Department. p. 4.
783:
755:
726:
217:, who first described it in 1854.
126:It was initially rejected by the
1918:
1917:
1590:
485:
158:used it for communication among
1014:
975:
963:
951:
928:
910:
895:
107:, who heavily promoted its use.
16:Early block substitution cipher
1779:Information-theoretic security
1036:Gaines, Helen Fouché (1956) ,
866:
854:
839:
822:
712:
703:
563:messages, they were broken at
204:
1:
1029:
181:
829:Reid, Thomas Wemyss (1899).
7:
1895:Message authentication code
1850:Cryptographic hash function
1663:Cryptographic hash function
1021:Listener crossword database
733:Christensen, Chris (2006).
684:
10:
1969:
1774:Harvest now, decrypt later
419:Clarification with picture
271:
95:
45:Wheatstone–Playfair cipher
18:
1913:
1890:Post-quantum cryptography
1842:
1598:
1560:
1507:
1479:
1451:
1391:
1353:
1285:
1259:
1216:
1183:
1172:
1134:
1130:
1008:10.1080/02684528708431890
622:The World War 2 thriller
472:
461:
450:
439:
428:
156:Government of New Zealand
154:During World War II, the
1880:Quantum key distribution
1870:Authenticated encryption
1725:Random number generation
918:Mauborgne, Joseph Oswald
696:
571:Use in modern crosswords
470:
459:
448:
437:
170:in the Pacific Islands.
83:and rather more complex
62:, but bears the name of
19:Not to be confused with
1875:Public-key cryptography
1865:Symmetric-key algorithm
1668:Key derivation function
1628:Cryptographic primitive
1621:Authentication protocol
1611:Outline of cryptography
1606:History of cryptography
92:in order to be useful.
66:for promoting its use.
1616:Cryptographic protocol
1166:Classical cryptography
691:Topics in cryptography
658:York: The Map of Stars
218:
128:British Foreign Office
108:
32:
1769:End-to-end encryption
1715:Cryptojacking malware
902:Lord, Walter (2012).
846:Lord, Walter (2012).
735:"Polygraphic Ciphers"
520:shotgun hill climbing
212:
197:, published in 1914.
176:Royal Australian Navy
103:
29:
1885:Quantum cryptography
1809:Trusted timestamping
1525:Index of coincidence
1429:Reservehandverfahren
1072:Kahn, David (1996),
793:Klima, Rick (2018).
765:Kahn, David (1996).
669:Batwoman (TV series)
532:Field Manual 34-40-2
261:To decrypt, use the
1648:Cryptographic nonce
1544:Kasiski examination
1539:Information leakage
195:Joseph O. Mauborgne
81:substitution cipher
56:digram substitution
1953:English inventions
1754:Subliminal channel
1738:Pseudorandom noise
1685:Key (cryptography)
1520:Frequency analysis
1419:RasterschlĂĽssel 44
984:, pp. 198–207
644:In the audio book
604:In popular culture
577:cryptic crosswords
575:Advanced thematic
223:key word or phrase
219:
215:Charles Wheatstone
109:
89:frequency analysis
60:Charles Wheatstone
33:
21:Wadsworth's cipher
1948:Classical ciphers
1935:
1934:
1931:
1930:
1814:Key-based routing
1804:Trapdoor function
1675:Digital signature
1556:
1555:
1552:
1551:
1447:
1446:
936:Friedman, William
617:Dorothy L. Sayers
543:Dorothy L. Sayers
483:
482:
413:
412:
1960:
1921:
1920:
1749:Insecure channel
1585:
1578:
1571:
1562:
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1159:
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1132:
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804:. Archived from
799:
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762:
753:
752:
750:
748:
739:
730:
724:
720:The Codebreakers
716:
710:
707:
677:S. (Dorst novel)
651:: God of Thunder
625:The Trojan Horse
612:Have His Carcase
548:Have His Carcase
545:' mystery novel
426:
388:
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324:
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199:William Friedman
1968:
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1218:Polybius square
1212:
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1168:
1163:
1107:Playfair Cipher
1093:
1084:
1057:Smith, Michael
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556:Double Playfair
488:
478:Hence, OR → IO
476:
467:Hence, OR → RW
465:
456:Hence, OR → ZX
454:
445:Hence, OR → BY
443:
434:Hence, OR → YZ
432:
421:
274:
230:Polybius square
207:
184:
174:established by
164:Chatham Islands
136:Second Boer War
98:
85:Vigenère cipher
41:Playfair square
37:Playfair cipher
24:
17:
12:
11:
5:
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1900:Random numbers
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1824:Garlic routing
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1705:Key stretching
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1424:Reihenschieber
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1091:External links
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1083:978-0684831305
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1799:Shared secret
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1658:Hash function
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1633:Cryptanalysis
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1508:Cryptanalysis
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1481:Steganography
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1355:Transposition
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1051:0-486-20097-3
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938:(June 1942).
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884:on 2011-11-12
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811:on 2017-10-13
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673:
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656:In the novel
655:
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64:Lord Playfair
61:
57:
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42:
38:
28:
22:
1855:Block cipher
1700:Key schedule
1690:Key exchange
1680:Kleptography
1643:Cryptosystem
1592:Cryptography
1414:One-time pad
1287:Substitution
1266:
1076:, Scribner,
1073:
1058:
1039:
1016:
999:
995:
989:
977:
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886:. Retrieved
882:the original
877:
868:
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831:
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813:. Retrieved
806:the original
801:
769:. Scribner.
766:
745:. Retrieved
741:
728:
719:
714:
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675:
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636:
635:In the film
623:
610:
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582:The Listener
581:
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285:
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153:
148:smoke shells
144:World War II
133:
125:
110:
76:
70:
68:
47:is a manual
44:
40:
36:
34:
1843:Mathematics
1834:Mix network
1466:Code talker
1345:Running key
1277:Four-square
982:Gaines 1956
970:Gaines 1956
958:Gaines 1956
863:, Chapter 8
647:Rogue Angel
508:four-square
205:Description
188:World War I
160:New Zealand
140:World War I
1942:Categories
1794:Ciphertext
1764:Decryption
1759:Encryption
1720:Ransomware
1515:Cryptogram
1409:Kama Sutra
1378:Rail fence
1373:Myszkowski
1320:Chaocipher
1272:Two-square
1251:VIC cipher
1203:Trithemius
1030:References
888:2011-12-24
815:2018-01-09
747:January 9,
662:Laura Ruby
609:The novel
512:two-square
496:ciphertext
182:Superseded
166:, and the
117:telegraphy
113:Wheatstone
52:encryption
1784:Plaintext
1439:Solitaire
1177:by family
1044:, Dover,
589:The Times
584:Crossword
561:pro forma
492:plaintext
49:symmetric
1923:Category
1829:Kademlia
1789:Codetext
1732:(CSPRNG)
1527:(Units:
1363:Columnar
1310:Beaufort
1267:Playfair
1241:Tap code
1236:Nihilist
1208:Vigenère
920:(1914).
685:See also
249:column).
1599:General
1305:Autokey
1193:Alberti
1174:Ciphers
272:Example
263:inverse
138:and in
96:History
77:digrams
72:bigrams
1710:Keygen
1494:Grille
1434:Slidex
1368:Double
1335:Pigpen
1315:Caesar
1300:Atbash
1295:Affine
1260:Square
1246:Trifid
1226:ADFGVX
1198:Enigma
1080:
1065:
1048:
773:
162:, the
1740:(PRN)
1489:Bacon
1453:Codes
1404:DRYAD
1399:BATCO
1392:Other
1383:Route
1340:ROT13
1325:Great
1231:Bifid
945:(PDF)
809:(PDF)
798:(PDF)
738:(PDF)
697:Notes
579:like
245:row).
31:"BM".
1531:and
1499:Null
1471:Poem
1461:Book
1330:Hill
1078:ISBN
1063:ISBN
1046:ISBN
771:ISBN
749:2018
510:and
494:and
35:The
1533:Nat
1529:Ban
1004:doi
628:by
615:by
473:5)
462:4)
451:3)
440:2)
429:1)
255:row
241:do.
75:or
43:or
39:or
1944::
998:.
876:.
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785:^
757:^
740:.
538:.
190:.
1584:e
1577:t
1570:v
1535:)
1158:e
1151:t
1144:v
1010:.
1006::
1000:2
891:.
818:.
779:.
751:.
671:.
23:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
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