The Vigenère cipher uses a 26×26 tablewith A to Z as the row heading and column headingThis table is usually referred to as the Vigenère Tableau,Vigenère Table orVigenère Square.We shall use Vigenère Table.The first row of this table has the 26 English letters.Starting with the second row, each row has the lettersshifted to the left one position in a cyclic way.For example, when B is shifted to the first position on the second row,the letter A moves to the end.
In addition to the plaintext, the Vigenère cipher also requires a keyword,which is repeated so that the total length is equal to that of the plaintext.For example, suppose the plaintext is MICHIGAN TECHNOLOGICAL UNIVERSITYand the keyword is HOUGHTON.Then, the keyword must be repeated as follows:
MICHIGAN TECHNOLOGICAL UNIVERSITYHOUGHTON HOUGHTONHOUGH TONHOUGNTO
We follow the tradition by removing all spaces and punctuation,converting all letters to upper case, anddividing the result into 5-letter blocks.As a result, the above plaintext and keyword become the following:
MICHI GANTE CHNOL OGICA LUNIV ERSIT YHOUGH TONHO UGHTO NHOUG HTONH OUGHT O
To encrypt, pick a letter in the plaintext and its corresponding letterin the keyword,use the keyword letter and the plaintext letter as the row index and column index, respectively,and the entry at the row-column intersection is the letter in the ciphertext.For example, the first letter in the plaintext is M and its corresponding keyword letter is H.This means that the row of H and the column of M are used,and the entry T at the intersection is the encrypted result.
Similarly, since the letter N in MICHIGAN corresponds to the letter N in the keyword,the entry at the intersection of row N and column N is Awhich is the encrypted letter in the ciphertext
Repeating this process until all plaintext letters are processed, the ciphertext is TWWNPZOA ASWNUHZBNWWGS NBVCSLYPMM.The following has the plaintext, repeated keyword and ciphertext aligned together.
MICHI GANTE CHNOL OGICA LUNIV ERSIT YHOUGH TONHO UGHTO NHOUG HTONH OUGHT OTWWNP ZOAAS WNUHZ BNWWG SNBVC SLYPM M
To decrypt, pick a letter in the ciphertext and its corresponding letterin the keyword,use the keyword letter to find the corresponding row,and the letter heading of the column that contains the ciphertext letter is the needed plaintext letter.For example, to decrypt the first letter T in the ciphertext,we find the corresponding letter H in the keyword.Then, the row of H is used to find the corresponding letter Tand the column that contains T provides the plaintext letter M(see the above figures).Consider the fifth letter P in the ciphertext.This letter corresponds to the keyword letter Handrow H is used to find P.Since P is on column I,the corresponding plaintext letter is I.
FAQs
When the vigenere table is not given, the encryption and decryption are done by Vigenar algebraically formula in this method (convert the letters (A-Z) into the numbers (0-25)). If any case (Di) value becomes negative (-ve), in this case, we will add 26 in the negative value. Where, E denotes the encryption.
How do I decode my Vigenère code? ›
Decryption: Decryption is performed by going to the row in the table corresponding to the key, finding the position of the ciphertext letter in this row, and then using the column's label as the plaintext. For example, in row A (from AYUSH), the ciphertext G appears in column G, which is the first plaintext letter.
What type of cipher is a Vigenère cipher? ›
Vigenère cipher, type of substitution cipher used for data encryption in which the original plaintext structure is somewhat concealed in the ciphertext by using several different monoalphabetic substitution ciphers rather than just one; the code key specifies which particular substitution is to be employed for ...
What is cipher encryption and decryption? ›
Encryption is the process by which a readable message is converted to an unreadable form to prevent unauthorized parties from reading it. Decryption is the process of converting an encrypted message back to its original (readable) format. The original message is called the plaintext message.
Is Vigenère cipher easy to crack? ›
A Vigenère cipher is difficult to crack using brute-force because each letter in a message could be encoded as any of the 26 26 26 letters. Because the encoding of the message depends on the keyword used, a given message could be encoded in 2 6 k 26^k 26k ways, where k k k is the length of the keyword.
How is Vigenère cipher broken? ›
In 1863, a Prussian major named Kasiski proposed a method for breaking a Vigenere cipher that consisted of finding the length of the keyword and then dividing the message into that many simple substitution cryptograms. Frequency analysis could then be used to solve the resulting simple substitutions.
Can you decode a Vigenère cipher without a key? ›
Decoding a Vigenere cipher without the key is very difficult - you first need to find the length of the key, before identifying what the key is and then finally deciphering the message.
What is the hardest cipher to decode? ›
Vigenère cipher
It is considered one of the most difficult historical ciphers to crack, primarily due to its polyalphabetic nature. Polyalphabetic Substitution: The cipher uses multiple alphabets to encode the plaintext, making it more resistant to frequency analysis attacks.
How to solve a cipher with a key? ›
To decode a substitution cipher with a key, you'll need to replace each letter in the encrypted message with the corresponding letter from the key. For example, if the key says "A" corresponds to "D", you'd replace every "A" in the encrypted message with a "D". By following the key, you can decipher the entire message.
What are the advantages of the Vigenère cipher? ›
Advantages of the Vigenère Cipher: Polyalphabetic Substitution: Unlike simpler ciphers like the Caesar cipher, the Vigenère cipher is polyalphabetic, meaning that each letter in the plaintext is potentially encrypted using different keys, making it more resistant to simple frequency analysis.
In the Vigenère Cipher, we choose a word or phrase as our encryption key. We then convert it to a sequence of numbers (again using a=0, b=1, ..., z=25), and apply a different shift to the plaintext corresponding to the letters in the keyword. When we use up the shifts from the keyword, we repeat it again.
How to decrypt cipher code? ›
All substitution ciphers can be cracked by using the following tips:
- Scan through the cipher, looking for single-letter words. ...
- Count how many times each symbol appears in the puzzle. ...
- Pencil in your guesses over the ciphertext. ...
- Look for apostrophes. ...
- Look for repeating letter patterns.
To encrypt more than a small amount of data, symmetric encryption is used. A symmetric key is used during both the encryption and decryption processes. To decrypt a particular piece of ciphertext, the key that was used to encrypt the data must be used.
How are ciphers used today? ›
In a virtual private network (VPN), a cipher plays an essential role in securing your data as it travels over the internet. The VPN uses a cipher to encrypt your data before it leaves your device, ensuring that it can't be read by anyone who intercepts it.
What is encryption and decryption in DES cipher? ›
DES is a block cipher, as shown in Fig. 6.1. At the encryption site, DES takes a 64-bit plaintext and creates a 64-bit ciphertext; at the decryption site, DES takes a 64-bit ciphertext and creates a 64-bit block of plaintext. The same 56-bit cipher key is used for both encryption and decryption.
What is encrypted and decrypt? ›
Encryption is the process of translating plain text data (plaintext) into something that appears to be random and meaningless (ciphertext). Decryption is the process of converting ciphertext back to plaintext.
What is Feistel cipher structure encryption and decryption? ›
Feistel cipher may have invertible, non-invertible and self invertible components in its design. Same encryption as well as decryption algorithm is used. A separate key is used for each round. However same round keys are used for encryption as well as decryption.
What is cryptanalysis of the Vigenère cipher? ›
Cryptanalysis of the Vigenère cipher has three steps: obtaining the key; determining the length of the key and determining the key characters. Then, it is possible to decrypt the ciphertext. The index of coincidence (IC) for keyword length can be used to do this. The accuracy for plaintext is 100%, with no mistakes.
