Contoh Program Vigenere Cipher
Ciphers
In this tutorial you will learn about vigenere cipher in C and C for encryption and decryption. Vigenere Cipher is kind of polyalphabetic substitution method. It is used for encryption of alphabetic text. For encryption and decryption Vigenere Cipher Table is used in which alphabets from A to Z are written in 26 rows. Also Read: Also Read: Vigenere Cipher Encryption Message Text: THECRAZYPROGRAMMER Key: HELLO Here we have to obtain a new key by repeating the given key till its length become equal to original message length. New Generated Key: HELLOHELLOHELLOHEL For encryption take first letter of message and new key i.e. Take the alphabet in Vigenere Cipher Table where T row and H column coincides i.e.
Repeat the same process for all remaining alphabets in message text. Finally the encrypted message text is: Encrypted Message: ALPNFHDJAFVKCLATIC The algorithm can be expressed in algebraic form as given below. The cipher text can be generated by below equation. E i = (P i + K i) mod 26 Here P is plain text and K is key. Vigenere Cipher Decryption Encrypted Message: ALPNFHDJAFVKCLATIC Key: HELLO New Generated Key: HELLOHELLOHELLOHEL Take first alphabet of encrypted message and generated key i.e.
Analyze Vigenere Cipher Table, look for alphabet A in column H, the corresponding row will be the first alphabet of original message i.e. Repeat the same process for all the alphabets in encrypted message. Original Message: THECRAZYPROGRAMMER Above process can be represented in algebraic form by following equation. P i = (E i – K i + 26) mod 26 We will use above algebraic equations in the program. Program for Vigenere Cipher in C.
The Autokey Cipher does not suffer from this weakness, as the repeating nature of the keystream is not used. However, even though it is more secure, it is still not impossible to break the Autokey Cipher.
The weakness here is that it is likely that some common words will have been used in the plaintext, and thus also in the keystream. For example 'the' is likely to appear in the keystream somewhere, and so by trying this everywhere we can identify other bits of likely plaintext, and put these back in the keystream, and so on. There are several parts to this system that worked well in this example.
The first word we chose to check, 'THE', was indeed in the plaintext. In reality, it may take a few goes to find a word that does appear. We also found a sensible plaintext segment on our second go with 'ako'. We could have tried many other possibilities before getting to this one.
Beeji is unable to go with her, as she twists her ankle. She decides to talk to Maanvi about it. Meri behna hai. Maanvi takes lunch for Monty. Viraat leaves for his 2 months world tour. Jeevika overhears her, and becomes disturbed.
The final guess of the keyword relied on it being a word. To make the encryption more secure, they might have used a non-sensical 'word', which would have slowed us down as well.