A cipher enables a secret way of writing a message to hide or disguise the actual message. A cipher is used to change the plain text message into an enciphered message that others cannot understand. A cipher is used to rearrange, substitute, and change the original characters in the message into secret codes that the sender and the receiver only know about or can know about.
For example, a simple way to use a cipher is to use a Substitution Cipher such as below. The alphabet ‘A’ will be replaced with ‘Z’, the alphabet ‘B’ will be replaced with ‘Y’, and so on as shown below. So, if the message is “LEAVING TOMORROW” then the enciphered message or the cipher text will be “PVZESNT GMOJJMD”. This message will not be understood by any intermediaries who are carrying or seeing the message.
Similarly, a Caesar Cipher is the one where the character ‘D’ is replaced with ‘A’, and so on.
Another type of cipher is the Vernam Cipher which uses a key of the same length as the actual message and XORs the message with the key to produce the enciphered message.
Another type of cipher is the Transposition Cipher. In this case, the spaces in the message are truncated and then the length of the message is calculated and put in a matrix.
For example, the message is “DUMMIES RESUMED SERVICES TODAY”. This is of 27 characters after truncating the spaces “DUMMIESRESUMEDSERVICESTODAY”.
So, arrange it in a matrix of 3×9 as below. You can read it across the rows.
Now, take out the message across the columns, and it comes out as below.
“DSIUUCMMEMESIDTESOSEDRRAEVY” – This is the enciphered text with transposition cipher. Now, this cipher text becomes unrecognizable. And, once received the recipient knows that the text length is 27 and can only be arranged in 3×9 or 9×3 and read column wise or row wise. By doing this, the recipient can decipher the message to its original plain text.
All the ciphers are eventually a substitutional or a transposition cipher. In various algorithms such as AES and DES, variations of these ciphers are used with multiple rotations, substitutions, and transpositions of keys of different length.
Hope this post served as a basic primer on ciphers and cipher text, thank you.
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