Also Read: Caesar Cipher in Java (Encryption and Decryption) Also Read: Caesar Cipher in C and C++ [Encryption & Decryption] There are several … I'm struggling to get my head around the Vigenere Cipher when you know the length of the key but not what it is. Comment below if you have any queries related to above program for vigenere cipher in Java. Given cipher text of sufficient length, it’s really not very difficult (even trivial) given a tiny bit of computer power, and would be tedious but straight forward to do by hand. Given some text you suspect has been encrypted with a Vigenère cipher, extract the key and plaintext. In general, the Vigenere cipher can be cracked easily for longer texts with shorter keys. Previously I looked at the Vigenère cipher, but I did not have a working Python example.After some thought and consideration I came to the realisation that the Vigenère cipher is pretty much just a Caesar cipher with a shift that changes each letter, which then allowed me to figure out how to make it in Python. Vigenere Cipher. Also Read: Caesar Cipher in Java (Encryption and Decryption), Also Read: Hill Cipher in Java [Encryption and Decryption]. Vigenere Cipher is kind of polyalphabetic substitution method. What if your assumption that T becomes E is wrong? That's all I'm given, I'm told the key is an arbitrary set of letters that don't necessarily have to make up a word in the english language, … Codebreaking Without a Key Guessing the Key Length Our first step is to examine repetitions in the encrypted text so we can guess at the length of the key. The user is allowed to either encrypt/decrypt some text file or break a given ciphertext without knowing the key nor the key length. Caesar’s nephew Augustus learned the code from his uncle, but encrypted his messages with a shift of only one, but without wrapping around the alphabet. For Vigenère cipher decryption, let us first select the row where the key letter is located. In the end your text will be properly decrypted. vhxzeztbsfej uopwtzvbioik jcewsrttlwnf dlitrlvuwzak jtsddpqugsej This online calculator tries to decode Vigenère cipher without knowing the key. Codebreaking Without a Key Guessing the Key Length Our first step is to examine repetitions in the encrypted text so we can guess at the length of the key. Key: NEERAJ Let's see if this matches the known key by trying to encode S. So if I'm getting this right, which I don't, I should look at the Vigenere square. We have to generate a new key by repeating above key in cyclic order until its length becomes equal to length of plain text. Spanish Standard Mode v s Autokey Variant: The Autokey mode is a stronger variant of the cipher, where letters of the plaintext become part of the key. person_outline Timur schedule 2 years ago If you came here, you probably already know that is Vigenère cipher. The table consists of the alphabets written out 26 times in different rows, each alphabet shifted … This key brings a huge evolution into ciphers, because it allows the one that uses it to resist (in a certain way) to letters frequency analysis. Vigenère cipher/Cryptanalysis You are encouraged to solve this task according to the task description, using any language you may know. Analyze cipher text to calculate key … Here we have to obtain a key by repeating the given key till its length becomes equal to original message length. The Vigenere Cipher C program requires two inputs from the end user: Message; Key Use the following encrypted text: MOMUD EKAPV TQEFM … It is closely related to the Vigenere cipher, but uses a different method of generating the key. That's more effort, but it's what automatic Vigenere solvers typically do. In this technique we use a table of alphabets A to Z which are written in 26 rows which is also known as Vigenere Table. The Vigenère Autokey Cipher is a more secure variant of the ordinary Vigenère cipher. In this last step you saw how a variety of techniques can be used to decrypt a Caesar cipher, even without knowing the key. Caesar Cipher in Java (Encryption and Decryption), Hill Cipher in Java [Encryption and Decryption], How to Connect Java (JDBC) with MS Access Database, Java Socket Programming (Client Server Program), Difference between Hashtable and HashMap in Java, How Clean Coding Principles Can Help You Lower the TOC of Your Software Development Lifecycle, How to Connect Java (JDBC) with MySQL or Oracle Database. Required fields are marked *. There are several methods to break Vigenère, usually the outline is: Guess the length of the key. Again, that's more work. Indeed, Vigenere cipher introduced the concept of key to encrypt the data. Though the 'chiffre indéchiffrable' is easy to understand and implement, for three centuries it resisted all attempts to break it. I am not sure how you managed to decode this automatically. MNO, NOP, RST, STU. The result of the addition modulo 26 (26=the number of letter in the alphabet) gives the rank of the ciphered letter. It employs a form of polyalphabetic substitution. Assume you are given a 300 character encrypted message, encrypted in Vigenere cryptosystem, in which you know the plaintext word CRYPTOGRAPHY occurs exactly two times, and we know that the ciphertext sequence TICRMQUIRTJR is the encryption of CRYPTOGRAPHY. share | improve this question | follow | edited Feb 4 '18 at 16:19. The Files. The Autokey Cipher is a polyalphabetic substitution cipher. It encrypt the first letters in the same way as an ordinary Vigenère cipher, but after all letters in the key have been used it doesn't repeat the sequence. Patriot. Below is the implementation of vigenere cipher in java. You can also provide a link from the web. Well, that is exactly what we are going to do now. Think of a keyword that is shorter than the phrase or phrases you want to encipher. Click here to upload your image
German … Your email address will not be published. If you have a short text (like here), or a longer key, then it gets harder. Unknown key. Phrase LEMON, for example, defines the sequence of ROT11-ROT4-ROT12-ROT14-ROT13, which is repeated until all block of text is encrypted. I also mentioned that nowadays this cipher doesn’t offer any security, since it can be easly broken with the help of a computer. MD5 hash Variant Beaufort cipher Alphabetical substitution HMAC generator Hex & binary Cryptii. The program should handle keys and text of unequal length, and should capitalize everything and discard non-alphabetic characters. Thus the plain text is obtained as.eval(ez_write_tag([[250,250],'thejavaprogrammer_com-banner-1','ezslot_9',108,'0','0'])); We can express above decryption process in algebraic equation in following way.eval(ez_write_tag([[728,90],'thejavaprogrammer_com-large-leaderboard-2','ezslot_6',109,'0','0'])); For cipher text (E) and key (K), the plain text can be obtained as. I am new to cryptography kindly help to solve the following vigenere cipher problem with well defined steps. The name Vigenere cipher comes from the diplomat Blaise de Vigenere who described this encryption (along with others) in 1586, in its book "Traité des Chiffres". Vigenere Cipher is a polyalphabetic substitution technique that is used for encrypting and decrypting a message text. vegenere.py is the python3 file for decrypting the cipher. The number of places a letter is shifted in the alphabet can change for each letter in the message, which means the most … It was invented by Blaise de Vigenère in 1586, and is in general more secure than the Vigenere cipher. The only way I can think of would be to check for dictionary words in both the key and the resulting output, ignoring any keys which do not make sense. Method. Next what I did was take every sixth letter from the cipher text(modulo 6): huutgquveptkxvnhgqhtvtuvjtdvjqcowykiwvknecgttqwjhvptcgnqdereu. I don't know precisely what techniques they use. In the above table, check out the row of the key that starts with letter B and the ciphertext starts with letter K. this … A popular cross-table called Vigènere square is used to identify elements for encryption and decryption based on Vigenere Cipher algorithm. The Vigenère cipher (French pronunciation: [viʒnɛːʁ]) is a method of encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. (max 2 MiB). The Vigenère cipher consists of multiple Caesar ciphers in a sequence with different shift values. Vigenere Ciphering by adding letters In order to cipher a text, take the first letter of the message and the first letter of the key, add their value (letters have a value depending on their rank in the alphabet, starting with 0). For this example we will use: LIME [3] X Research source hrmwnuurseae ucsmnktyqwnc gnheepquvwai uiggmvvofmrp eaikaipoxlog Take first letter in cipher text and key, i.e. Vigenère-Cipher-Decrypter is a tool that attempts to decrypt certain data encrypted by the Vigenère cipher. In such cases, after how many uses would the key be considered insecure? In this technique we use a table of alphabets A to Z which are written in 26 rows which is also known as Vigenere Table. Original Message: THEJAVAPROGRAMMER phsfoltafded cnwgaigtlwyr nledlyqnsmrr dlieeeeoqwij reecieeaikai Lets understand encryption by one example. First step will be calculation or guessing the key length your text has been encrypted with. So the first shift probably turns one of M,N,R,S to T. Your other conspicuously common ciphertext ietter is Q, three before T. In those four cases, that would correspond to H,I,M,N. Method of encrypting alphabetic text by using a series of interwoven Caesar ciphers based on the letters of a keyword. How do I solve this Vigenere cipher. Sure, all else being equal the most frequent letter is most likely to be E. But there are plenty of other common letters in English. Look at which letter in the key would convert S to H. In this case it would be P, but that would say that the first letter of the key is P which it isn't. The Caesar Cipher is an encryption system that predates computers. encryption substitution-cipher vigenere. https://puzzling.stackexchange.com/questions/64546/how-do-i-solve-this-vigenere-cipher-unknown-key/64548#64548, How do I solve this Vigenere cipher. As an example you can crack the following cipher text with this tool: Altd hlbe tg lrncmwxpo kpxs evl ztrsuicp qptspf. The algorithm. Watch the full course at https://www.udacity.com/course/ud459 The only way to decode, or decrypt, the message is by knowing the “key”, or how the message was changed. Task. Unfortunately, those are all fairly plausible. Generated Key: NEERAJNEERAJNEERA. to calculate IC= [n (n – 1)]^–1 (summation [Fi (Fi – 1)]) where n is the number of character in cipher text, Fi is frequency of ith character and i ranges from 0 … Implement a Vigenère cypher, both encryption and decryption. Comment document.getElementById("comment").setAttribute( "id", "ab4803d53d2cd3348faef8070656bdd0" );document.getElementById("c210a4da35").setAttribute( "id", "comment" ); Save my name, email, and website in this browser for the next time I comment. Viewed 5k times 3 $\begingroup$ I have this cipher text: hrmwnuurseae ucsmnktyqwnc gnheepquvwai uiggmvvofmrp eaikaipoxlog tamkeykmxzev xiplhrvmifdf nizwsrhtijty gmxzexqohasf htmftvtrivwz vhxzeztbsfej uopwtzvbioik jcewsrttlwnf dlitrlvuwzak jtsddpqugsej … Instead it begins using letters from the plaintext as key. See the Wikipedia entry for more information. Is this true when the same key is used multiple times? Now take first letter of plain text and key, i.e. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. In my previous post I explained how the Vigenère cipher works and how to implement it in Rust. This is an implementation of Vigenere cipher in Java. This tool can decrypt Vigenère cipher with and without Key. So I came to the conclusion that T is probably E, sfferbfgpaevigysrbsegefgueogubnzhjvthgvypnreebhusgaenrybopcpf. Active 2 years, 7 months ago. Key: WELCOME. What you really want to be doing is looking at the whole frequency distribution from your every-sixth-letter text, and seeing what shift of it looks most like that of English. I have read the Vigenère cipher is secure as long as the key length is the same as the length of the data to be ciphered. This video is part of the Udacity course "Intro to Information Security". All these letter should have been encoded with the same letter from the key, so it's a simple shift cipher. vigenere cipher can be converted into plain by calculating index of coincidence (IC), this will determine the key length and then based on key length (lets say x), cipher will be grouped into x and on each group ceasar cryptanalysis will be applied. Vigenère cipher: Encrypt and decrypt online. Vigenere Cipher is a polyalphabetic substitution technique that is used for encrypting and decrypting a message text. This is because the patterns in the text are preserved by the encryption scheme. realistic. Let us continue with the example at hand. I can decipher text if I know the key but I'm confused as to how to work out what the key actually is. It uses the index of coincidence technique. The algorithm is quite simple. In a Vigenère cipher, common words such as "the" or "that" can be encrypted differently each time. Simply import the project in your IntelliJ IDEA and build it. This online calculator tries to decode Vigenère cipher without knowing the key. There are several methods for doing this. Your email address will not be published. So finally we get the encrypted text as.eval(ez_write_tag([[250,250],'thejavaprogrammer_com-medrectangle-4','ezslot_2',106,'0','0']));eval(ez_write_tag([[250,250],'thejavaprogrammer_com-medrectangle-4','ezslot_3',106,'0','1'])); We can express above process in algebraic equation in following way. H and E. Again analyze the table to find second letter of encrypted text. Basically, you guess the key length n, and then divide the message into n parts. Ask Question Asked 2 years, 7 months ago. This process is repeated for all the letters in plain text. Vigenère-Cipher-Decrypter. Then find the ciphertext’s position in that row. Besides the classical variant Beaufort ciphers and Autokey ciphers are supported as well. P. crassrobmlif wsmxikyevwsf ktassrirmwvf wsjsucvarvgi kezgujnylsty Yes. I have been able to find the key length of 6. T and W. Take the alphabet in Vigenere Cipher Table where T row and W column coincides i.e. For encryption take first letter of message and key i.e. Web app offering … Vigenere Cipher is a method of encrypting alphabetic text. So are there three consecutive letters that are all common in English? For plain text (P) and key (K), the cipher text can be obtained as. Vigenère cipher is the sequence of Caesar ciphers with different transformations (ROTX, see Caesar cipher). G. Here G is the first letter of encrypted or cipher text.eval(ez_write_tag([[580,400],'thejavaprogrammer_com-medrectangle-3','ezslot_4',105,'0','0'])); Now take second letter of plain text and key i.e. Then we have to crack the key using frequency analysis or guessing. Ideally, you would use a random key … As a rough approximation, look at those top three letters in your frequency list: T,V,U. Message: Thisistutorialspoint. Your main problem is that you were too quick to guess what the shift should be. Once this is done then the column tag of the respective ciphertext is the plaintext. G and N. Now take column N and look for letter G in it, the corrosponding row to letter G is T which is the first letter of plain text after decryption. tamkeykmxzev xiplhrvmifdf nizwsrhtijty gmxzexqohasf htmftvtrivwz Encryption is a technique used to send an encoded message. This online tool breaks Vigenère ciphers without knowing the key. Only the last two are plausible, and CEF has the merit that it's the only one that allows plaintext-E to be one of the common ciphertext letters. If the key cannot be cracked correctly, you may try to use some known plain text attacks. There are automated Vigenere solvers online. eaikaicnwoei gdmlhvteyfdv tlisvvqffjuk wsefdkjevwsk hovtrlvuwasr For example, first letter of text is transformed using ROT5, second - using ROT17, et cetera. ufyfeicl, (The key is "ceasar", but I have to know how to solve it without knowing the key.). After that you have EGH all quite common; in those four cases these would be XZA,YAB,CEF,DFG. T and N. See row T and column N in vigenere table, take the letter where row T and column N coincides i.e. However, … For one example I'm given cipher text and a key length of 6. There were no algorithms or supercomputers that could quickly decode an encrypted message. Unknown key. Vigenère cipher Decoder . This tool base supports you in analysing and breaking a vigenere cipher. Java Vigenere Cipher Program (Encryption and Decryption), //generate new key in cyclic manner equal to the length of original message, //String.valueOf() converts character array to String. 1,922 2 2 gold badges 9 9 silver badges 36 … The encrypted data is decrypted by frequencies of letters observed and the key length is detected by peaks observed in the encrypted … Better would be to compute some sort of measure of similarity between the distribution of ciphertext letters and shifted versions of the known distribution of English letters. For encryption and decryption Vigenere Cipher Table is used in which alphabets from A to Z are written in 26 rows. It uses a simple form of polyalphabetic substitution.A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets .The encryption of the original text is done using the Vigenère square or Vigenère table.. The sequence is defined by keyword, where each letter defines needed shift. The Caesar cipher is equivalent to a Vigenère cipher with just a one-letter secret key. Julius Caesar used this cipher in his private war-time correspondence, always with a shift of three. Even better would be not just to guess the six key letters independently, but to try to make distributions of digraphs, trigraphs, etc. These are three consecutive letters in the alphabet. Ei = (Pi + Ki) mod 26eval(ez_write_tag([[468,60],'thejavaprogrammer_com-box-4','ezslot_7',107,'0','0'])); Letâs understand decryption process with another example. Building. This is not the case for the Vigenère cipher, which is more complex. By clicking âPost Your Answerâ, you agree to our terms of service, privacy policy and cookie policy, 2021 Stack Exchange, Inc. user contributions under cc by-sa. Here you will get program for vigenere cipher in Java for both encryption and decryption. Repeate the same process for all the letters in cipher text. $ python Vigenere_cipher_mod.py Key: WHITE Decode text: -> Input text: en un lugar de la mancha de cuyo nombre no quiero acordarme -> Coded text: AU CG PQNIK HA SI FEJJPT HA JCRS JVUUVA UW JYELZH EYVZWENTM Decode text: -> Input text: AU CG PQNIK HA SI FEJJPT HA JCRS JVUUVA UW JYELZH EYVZWENTM -> Decoded text: en un lugar de la mancha de cuyo nombre no … It is used for encryption of alphabetic text. Years, 7 months ago the ciphered letter will be calculation or guessing key! If you have any queries related to above program for Vigenere cipher conclusion that T is probably E sfferbfgpaevigysrbsegefgueogubnzhjvthgvypnreebhusgaenrybopcpf. Once this is because the patterns in the text are preserved by the encryption scheme letter from the key the! Analysis or guessing the key length ), or a longer key, then gets! Based on Vigenere cipher md5 hash variant Beaufort cipher Alphabetical substitution HMAC generator Hex & binary Cryptii I came the... You have EGH all quite common ; in those four cases these would be XZA, YAB, CEF DFG... Discard non-alphabetic characters decryption ) how do I solve this Vigenere cipher be!, then it gets harder your text has been encrypted with using ROT5, second - using,! Introduced the concept of key to encrypt the data of text is encrypted to above program for Vigenere cipher Java..., extract the key be considered insecure came to the Vigenere cipher can be cracked,! How many uses would the key and plaintext common ; in those four cases these would be XZA,,. Same letter from the cipher text and key, i.e are there consecutive... In that row build it of encrypting alphabetic text by using a series of interwoven Caesar ciphers different. The following cipher text ( modulo 6 ): huutgquveptkxvnhgqhtvtuvjtdvjqcowykiwvknecgttqwjhvptcgnqdereu ( K ), the cipher length your has. Were too quick to guess what the shift should be the python3 file decrypting... A given ciphertext without knowing the key length of the ciphered letter key can not be cracked easily longer. Cypher, both encryption and decryption '' or `` that '' can be encrypted differently each time longer with. Encrypted with that '' can be cracked correctly, you may try to some. Upload your image ( max 2 MiB ) gives the rank of the but... Udacity course `` Intro to Information Security '' see Caesar cipher is a polyalphabetic substitution technique that used... Is located out what the key substitution HMAC generator Hex & binary Cryptii let. Of plain text the alphabet in Vigenere cipher both encryption and decryption how... In that row an example you can crack the key 's what automatic Vigenere solvers typically.... Step will be calculation or guessing select the row where the key actually is same is... Letters that are all common in English each letter defines needed shift algorithms supercomputers... Words such as `` the '' or `` that '' can be differently. Key i.e to either encrypt/decrypt some text file or break a given ciphertext without knowing the key, it. Shift of three binary Cryptii 'm given cipher text and a key by repeating the given key its! New to cryptography kindly help to solve the following Vigenere cipher problem with well defined steps supercomputers that quickly... What the shift should be the shift should be 7 months ago I can decipher if! You know the key length to original message length variant Beaufort cipher substitution... Be calculation or guessing is closely related to the Vigenere cipher can be obtained.! Tool that attempts to break it K ), or a longer key, then it gets.. Letter in cipher text with this tool can decrypt Vigenère cipher decryption, let us first select the row the. Vigenère, usually the outline is: guess the key length of the key not... Be obtained as an encryption system that predates computers number of letter in the alphabet in Vigenere cipher in private. You managed to decode Vigenère cipher, which is more complex words as... Or a longer key, i.e, both encryption and decryption Vigenere cipher is an encryption system predates! Algorithms or supercomputers that could quickly decode an encrypted message like here ), or longer. Kind of polyalphabetic substitution method 26 ( 26=the number of letter in cipher text with this tool base you... Vigènere square is used in which alphabets from a to Z are in. Of encrypting alphabetic text by using a series of interwoven Caesar ciphers with different transformations ROTX... Ztrsuicp qptspf: THEJAVAPROGRAMMER key: NEERAJNEERAJNEERA s position in that row are going to do now unequal length and... See row T and column n coincides i.e its length becomes equal to original message length encrypt data. Plaintext as key cipher introduced the concept of key to encrypt the data have! Letter should have been encoded with the same letter from the plaintext W. take the alphabet in Vigenere Table take. To length of plain text and a key length of plain text ( like here ), a. An encoded message text can be encrypted differently each time MiB vigenère cipher decoder without key hlbe! That are all common in English column coincides i.e for encryption take first letter text. … the Caesar cipher ) in cipher text can be cracked easily for longer texts with shorter keys substitution generator... If I know the key and plaintext based on the letters in cipher text key. Next what I did was take every sixth letter from the plaintext key... Introduced the concept of key to encrypt the data should capitalize everything and discard non-alphabetic characters common ; in four! Been able to find the key can not be cracked correctly, you guess the length of ordinary. You have a short text ( P ) and key, i.e a link the! Is more complex Z are written in 26 rows classical variant Beaufort ciphers and Autokey are... Can decrypt Vigenère cipher result of the Udacity course `` Intro to Information Security.! This is because the patterns in the text are preserved by the Vigenère cipher without knowing key. Repeate the same letter from the plaintext that attempts to break it ’ s position in that row generator... `` the '' or `` that '' can be obtained as end your text has been with... Approximation, look at those top three letters in cipher text and key, it.: Altd hlbe tg lrncmwxpo kpxs evl ztrsuicp qptspf there were no algorithms or supercomputers could! And plaintext: //puzzling.stackexchange.com/questions/64546/how-do-i-solve-this-vigenere-cipher-unknown-key/64548 # 64548, how do I solve this Vigenere Table... '' or `` that '' can be encrypted differently each time EGH all quite ;. Encryption take first letter of encrypted text column n coincides i.e queries related to conclusion. Encrypted with your IntelliJ IDEA and build it can decrypt Vigenère cipher decrypting the cipher the is... Generate a new key by repeating above key in cyclic order until its length becomes equal original... Some text file or break a given ciphertext without knowing the key plaintext! Encoded message by keyword, where each letter defines needed shift https: #... Xza, YAB, CEF, DFG to use some known plain text ( modulo 6 ): huutgquveptkxvnhgqhtvtuvjtdvjqcowykiwvknecgttqwjhvptcgnqdereu this... What the key outline is: guess the key letter is located, defines the sequence is defined keyword! Keyword, where each letter defines needed shift closely related to the Vigenere cipher where. Here we have to obtain a key length of 6 as `` the '' or `` ''. Alphabet in Vigenere Table, take the alphabet in Vigenere Table, take the in. What if your assumption that T becomes E is wrong properly decrypted guess what the shift should be )., CEF, DFG to encrypt the data repeating above key in order! As an example you can also provide a link from the cipher text can be correctly. Were too quick to guess what the key length of the ordinary Vigenère cipher differently each time in Vigenère... Below is the sequence of ROT11-ROT4-ROT12-ROT14-ROT13, which is more complex a rough approximation, look at top. Step will be calculation or guessing - using ROT17, et cetera shift of three could quickly decode an message!, first letter of plain text and key, i.e find second of... 26=The number of letter in the alphabet ) gives the rank of the ordinary Vigenère with! Will get program for Vigenere cipher Table where T row and W column coincides i.e Generated... Then it gets harder take first letter of message and key i.e length... Message length text with this tool: Altd hlbe tg lrncmwxpo kpxs evl ztrsuicp qptspf I been... To solve the following encrypted text: MOMUD EKAPV TQEFM … the Caesar cipher ) both encryption and ). Is kind of polyalphabetic substitution method substitution technique that is Vigenère cipher with a... Length n, and is in general more secure variant of the key actually is, first letter of is... Text can be cracked correctly, you probably already know that is used for and... Is exactly what we are going to do now to calculate key … Vigenere,... Then the column tag of the respective ciphertext is the sequence of ROT11-ROT4-ROT12-ROT14-ROT13 which. Is in general more secure variant of the Udacity course `` Intro to Information Security '' when... The project in your IntelliJ IDEA and build it used this cipher in Java you to. Needed shift to decrypt certain data encrypted by the encryption scheme below is the sequence of ROT11-ROT4-ROT12-ROT14-ROT13, is. To either encrypt/decrypt some text you suspect has been encrypted with a Vigenère cipher the concept of key to the... Text file or break a given ciphertext without knowing the key can not be cracked,... But uses a different method of generating the key length of 6 ( number! Related to the conclusion that T becomes E is wrong until its length becomes equal length! Is the plaintext so I came to the Vigenere cipher the respective ciphertext is the plaintext key. To solve the following encrypted text: MOMUD EKAPV TQEFM … the Vigenère Autokey cipher is more.