89:, a square with 26 copies of the alphabet, the first line starting with 'A', the next line starting with 'B' etc. Instead of a single letter, a short agreed-upon keyword is used, and the key is generated by writing down the primer and then the rest of the message, as in Vigenère's version. To encrypt a plaintext, the row with the first letter of the message and the column with the first letter of the key are located. The letter in which the row and the column cross is the ciphertext letter.
20:
1284:
226:
In each case, the resulting plaintext appears almost random because the key is not aligned for most of the ciphertext. However, examining the results can suggest locations of the key being properly aligned. In those cases, the resulting decrypted text is potentially part of a word. In this example,
132:
The first letter of the key, Q, would then be taken, and that row would be found in a tabula recta. That column for the first letter of the ciphertext would be looked across, also Q in this case, and the letter to the top would be retrieved, A. Now, that letter would be added to the end of the key:
222:
ciphertext: WMP MMX XAE YHB RYO CA key: THE THE THE THE THE .. plaintext: dfl tft eta fax yrk .. ciphertext: W MPM MXX AEY HBR YOC A key: . THE THE THE THE THE . plaintext: . tii tqt hxu oun fhy . ciphertext: WM PMM XXA EYH BRY OCA key: .. THE THE THE THE THE plaintext: ..
294:
is caused by the feedback from the relationship between plaintext and key. A three-character guess reveals six more characters (three on each side), which then reveal further characters, creating a cascade effect. That allows incorrect guesses to be ruled out quickly.
179:
A crucial weakness of the system, however, is that the plaintext is part of the key. That means that the key will likely contain common words at various points. The key can be attacked by using a dictionary of common words,
82:
with a reciprocal table of ten alphabets. Vigenère's version used an agreed-upon letter of the alphabet as a primer, making the key by writing down that letter and then the rest of the message.
235:. Examining the results, a number of fragments that are possibly words can be seen and others can be eliminated. Then, the plaintext fragments can be sorted in their order of likelihood:
1264:
1094:
211:
The attacker receives only the ciphertext and can attack the text by selecting a word that is likely to appear in the plaintext. In this example, the attacker selects the word
168:
Autokey ciphers are somewhat more secure than polyalphabetic ciphers that use fixed keys since the key does not repeat within a single message. Therefore, methods like the
284:
Because the plaintext guesses have an effect on the key 4 characters to the left, feedback on correct and incorrect guesses is given. The gaps can quickly be filled in:
521:
947:
51:. The key is generated from the message in some automated fashion, sometimes by selecting certain letters from the text or, more commonly, by adding a short
408:
353:
245:) also appears in the plaintext shifted left. Thus, by guessing keyword lengths (probably between 3 and 12), more plaintext and key can be revealed.
241:
A correct plaintext fragment is also going to appear in the key, shifted right by the length of the keyword. Similarly, the guessed key fragment (
145:
Then, since the next letter in the key is U and the next letter in the ciphertext is N, the U row is looked across to find the N to retrieve T:
70:
to determine the next element in the keystream. A text-autokey uses the previous message text to determine the next element in the keystream.
514:
940:
392:
188:
etc. and by attempting the decryption of the message by moving that word through the key until potentially-readable text appears.
439:
Il vero modo di scrivere in cifra con facilità, prestezza, et securezza di Misser Giovan
Battista Bellaso, gentil’huomo bresciano
507:
98:
1143:
933:
231:
is the start of the original plaintext and so it is highly unlikely either that the first three letters of the key are
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1214:
1027:
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1138:
486:
1254:
412:
1244:
1234:
1089:
357:
160:
With Vigenère's autokey cipher, a single mistake in encryption renders the rest of the message unintelligible.
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992:
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shift by 6: ciphertext: WMPMMXXAEYHBRYOCA key: ....TQT...THE...O plaintext: ....the...oun...m
258:
shift by 5: ciphertext: WMPMMXXAEYHBRYOCA key: .....EQW..THE..OU plaintext: .....the..oun..og
255:
shift by 4: ciphertext: WMPMMXXAEYHBRYOCA key: ......ETA.THE.OUN plaintext: ......the.oun.ain
1249:
1173:
889:
793:
747:
737:
732:
727:
719:
176:
analysis will not work on the ciphertext, unlike for similar ciphers that use a single repeated key.
173:
157:
That continues until the entire key is reconstructed, when the primer can be removed from the start.
205:
The message is then encrypted by using the key and the substitution alphabets, here a tabula recta:
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651:
169:
1118:
1102:
1049:
884:
803:
709:
641:
48:
572:
329:
264:
A shift of 4 can be seen to look good (both of the others have unlikely Qs) and so the revealed
199:: To start, the autokey would be constructed by placing the primer at the front of the message:
19:
1178:
1168:
1039:
853:
773:
742:
636:
567:
388:
382:
1113:
530:
126:
To decrypt the message, the recipient would start by writing down the agreed-upon keyword.
674:
631:
600:
582:
271:
ciphertext: WMPMMXXAEYHBRYOCA key: ..LTM.ETA.THE.OUN plaintext: ..eta.the.oun.ain
208:
plaintext: meetatthefountain key: KILTMEETATTHEFOUN ciphertext: WMPMMXXAEYHBRYOCA
1188:
1108:
1069:
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893:
788:
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as a potential part of the original message and then attempts to decode it by placing
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1007:
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24:
120:
Plaintext: attackatdawn Key: QUEENLYATTACKATDAWN Ciphertext: QNXEPVYTWTWP
1198:
863:
830:
825:
694:
238:
unlikely ←——————————————————→ promising eqw dfl tqt ... ... ... ... eta oun fax
1158:
1128:
1123:
1084:
897:
879:
684:
615:
304:
252:, possibly after wasting some time with the others, results in the following:
202:
plaintext: meetatthefountain primer: KILT autokey: KILTMEETATTHEFOUN
1148:
835:
67:
44:
1193:
1153:
605:
274:
A lot can be worked with now. The keyword is probably 4 characters long (
185:
1074:
798:
664:
538:
181:
40:
768:
763:
704:
18:
105:, and appends the message to it. For example, if the keyword is
929:
503:
381:
Hoffstein, Jeffrey; Pipher, Jill; Silverman, Joseph (2014).
66:
ciphers. A key-autokey cipher uses previous members of the
1095:
Cryptographically secure pseudorandom number generator
123:
The ciphertext message would thus be "QNXEPVYTWTWP".
491:
1207:
963:
872:
844:
816:
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718:
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581:
548:
537:
446:
Traicté des chiffres ou secrètes manières d’escrire
114:
110:
106:
487:A Javascript implementation of the Autokey cipher
455:, “The Cryptogram”, vol. LX n. 2, Wilbraham 1994.
469:, “The Cryptogram”, vol. LXXIV n. 3, Plano 2008.
101:, starts with a relatively-short keyword, the
97:The autokey cipher, as used by members of the
941:
515:
268:can be shifted back by 4 into the plaintext:
8:
384:An Introduction to Mathematical Cryptography
448:, Abel l’Angelier, Paris 1586. ff. 46r-49v.
376:
374:
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934:
926:
545:
522:
508:
500:
496:
492:
321:
278:), and some of the message is visible:
219:at every possible location in the key:
58:There are two forms of autokey cipher:
16:Classic polyalphabet encryption system
7:
483:- AutoKey Cipher Decoder and Encoder
78:This cipher was invented in 1586 by
462:, “Cryptologia” 30 (1):39-51, 2006.
411:. Asecuritysite.com. Archived from
356:. Asecuritysite.com. Archived from
43:that incorporates the message (the
195:encrypted with the primer keyword
14:
441:, Iacobo Britannico, Bressa 1564.
1283:
1282:
467:Vigenère and Autokey. An Update
99:American Cryptogram Association
1144:Information-theoretic security
453:Early Forms of the Porta Table
27:for use with an autokey cipher
1:
55:to the front of the message.
465:LABRONICUS (Buonafalce, A),
460:Bellaso’s Reciprocal Ciphers
451:LABRONICUS (Buonafalce, A),
191:Consider an example message
85:More popular autokeys use a
1260:Message authentication code
1215:Cryptographic hash function
1028:Cryptographic hash function
227:it is highly unlikely that
1334:
1139:Harvest now, decrypt later
437:Bellaso, Giovan Battista,
1278:
1255:Post-quantum cryptography
925:
499:
495:
387:. Springer. p. 288.
1245:Quantum key distribution
1235:Authenticated encryption
1090:Random number generation
113:, then the key would be
1240:Public-key cryptography
1230:Symmetric-key algorithm
1033:Key derivation function
993:Cryptographic primitive
986:Authentication protocol
976:Outline of cryptography
971:History of cryptography
981:Cryptographic protocol
531:Classical cryptography
28:
1134:End-to-end encryption
1080:Cryptojacking malware
458:Buonafalce, Augusto,
444:Vigenère, Blaise de,
310:Cipher Block Chaining
129:QNXEPVYTWTWP QUEENLY
22:
1250:Quantum cryptography
1174:Trusted timestamping
890:Index of coincidence
794:Reservehandverfahren
409:"Autokey Calculator"
354:"Autokey Calculator"
223:wfi eqw lrd iku vvw
193:meet at the fountain
174:index of coincidence
148:QNXEPVYTWTWP QUEENLY
136:QNXEPVYTWTWP QUEENLY
1013:Cryptographic nonce
909:Kasiski examination
904:Information leakage
481:Secret Code Breaker
170:Kasiski examination
115:QUEENLYATTACKATDAWN
109:and the message is
35:(also known as the
1119:Subliminal channel
1103:Pseudorandom noise
1050:Key (cryptography)
885:Frequency analysis
784:Rasterschlüssel 44
287:meetatthefountain
281:m.eta.the.oun.ain
80:Blaise de Vigenère
29:
1313:Classical ciphers
1300:
1299:
1296:
1295:
1179:Key-based routing
1169:Trapdoor function
1040:Digital signature
921:
920:
917:
916:
812:
811:
330:"Vigenère Cipher"
248:Trying that with
1325:
1286:
1285:
1114:Insecure channel
950:
943:
936:
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37:autoclave cipher
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583:Polybius square
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12:
11:
5:
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1318:Stream ciphers
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1265:Random numbers
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1189:Garlic routing
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1109:Secure channel
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1070:Key stretching
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1018:Cryptovirology
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1003:Cryptocurrency
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789:Reihenschieber
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550:Polyalphabetic
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475:External links
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111:attack at dawn
94:
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33:autokey cipher
15:
13:
10:
9:
6:
4:
3:
2:
1330:
1319:
1316:
1314:
1311:
1310:
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1271:
1270:Steganography
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1225:Stream cipher
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1213:
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1184:Onion routing
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1165:
1164:Shared secret
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1066:
1063:
1061:
1060:Key generator
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1056:
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1048:
1046:
1043:
1041:
1038:
1034:
1031:
1029:
1026:
1025:
1024:
1023:Hash function
1021:
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1009:
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1004:
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998:Cryptanalysis
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873:Cryptanalysis
871:
865:
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849:
847:
846:Steganography
843:
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736:
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731:
729:
726:
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723:
721:
720:Transposition
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436:
435:
430:
415:on 2013-12-03
414:
410:
404:
401:
396:
394:9781493917112
390:
386:
385:
377:
375:
371:
360:on 2013-12-02
359:
355:
349:
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335:
334:Crypto Corner
331:
325:
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292:cryptanalysis
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164:Cryptanalysis
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46:
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38:
34:
26:
21:
1220:Block cipher
1065:Key schedule
1055:Key exchange
1045:Kleptography
1008:Cryptosystem
957:Cryptography
779:One-time pad
669:
652:Substitution
466:
459:
452:
445:
438:
417:. Retrieved
413:the original
403:
383:
362:. Retrieved
358:the original
348:
337:. Retrieved
333:
324:
290:The ease of
289:
283:
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210:
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190:
178:
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125:
122:
102:
96:
87:tabula recta
84:
77:
64:text-autokey
63:
59:
57:
52:
36:
32:
30:
25:tabula recta
1208:Mathematics
1199:Mix network
831:Code talker
710:Running key
642:Four-square
60:key-autokey
47:) into the
1307:Categories
1159:Ciphertext
1129:Decryption
1124:Encryption
1085:Ransomware
880:Cryptogram
774:Kama Sutra
743:Rail fence
738:Myszkowski
685:Chaocipher
637:Two-square
616:VIC cipher
568:Trithemius
431:References
419:2012-12-26
364:2012-12-26
339:2018-08-13
305:Chaocipher
53:primer key
1149:Plaintext
804:Solitaire
542:by family
68:keystream
45:plaintext
1288:Category
1194:Kademlia
1154:Codetext
1097:(CSPRNG)
892:(Units:
728:Columnar
675:Beaufort
632:Playfair
606:Tap code
601:Nihilist
573:Vigenère
299:See also
186:trigrams
964:General
670:Autokey
558:Alberti
539:Ciphers
182:bigrams
107:QUEENLY
74:History
39:) is a
1075:Keygen
859:Grille
799:Slidex
733:Double
700:Pigpen
680:Caesar
665:Atbash
660:Affine
625:Square
611:Trifid
591:ADFGVX
563:Enigma
391:
103:primer
93:Method
41:cipher
1105:(PRN)
854:Bacon
818:Codes
769:DRYAD
764:BATCO
757:Other
748:Route
705:ROT13
690:Great
596:Bifid
316:Notes
896:and
864:Null
836:Poem
826:Book
695:Hill
389:ISBN
276:..LT
197:KILT
62:and
898:Nat
894:Ban
266:ETA
250:oun
243:THE
233:THE
229:dfl
217:THE
213:the
172:or
49:key
31:An
1309::
373:^
332:.
184:,
153:at
150:AT
117:.
23:A
949:e
942:t
935:v
900:)
523:e
516:t
509:v
422:.
397:.
367:.
342:.
141:a
138:A
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