A cipher is an encrypted message or a cryptographic system that rearranges symbols or letters. Julius Caesar used a basic cipher to send messages. Simple ciphers can be cracked, but more complex ones exist. The encryption key is essential for correct transmission and key management is crucial for security.
A cipher can generally refer to an encrypted message. It can also refer more specifically to a cryptographic system in which symbols or groups of symbols represent a section of text—single or longer letters—and/or units of text are rearranged according to a set of rules that have been predetermined. The encryption key is the information needed to use encryption.
Ciphers start with a simple text message, the words someone wants to hide. The plaintext is manipulated twice. First, it’s encrypted to hide the meaning. The plaintext message is then called ciphered or scrambled and may be called ciphertext. Then it is decrypted to reveal the plaintext again. In any case, the encryption key is required.
There are different levels of encryption complexity. The most basic cipher has a plaintext alphabet, which is the usual alphabet of the English language, and a ciphertext alphabet, which is the same alphabet that starts with a letter other than a and with the letters having been removed from the front labeled on the back. An ancient and famous use of a cipher was made by Julius Caesar, who used this encryption method to send messages to his generals.
Plain text alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Ciphertext alphabet: DEFGHIJKLMNOPQRSTUVWXYZABC
A total of 25 different digits can be created by shifting the cipher alphabet to start with every letter besides . But even with so many possibilities, an unauthorized person who gets hold of the encrypted message and knows that it’s a cipher has a straightforward, albeit tedious, path to figuring it out, even without access to the encryption key.
To send a message, the encryption key is used to determine the alphabet of the ciphertext. So for each plaintext letter you want to transmit, you write the ciphertext letter in its place. So, if you decide to encrypt wiseGEEK, you’d end up with:
zlvhJHHN
To decrypt the ciphertext, one would use the cipherkey to construct the ciphertext alphabet and substitute the plaintext letter for each ciphertext letter.
There are several obvious clues in the cipher itself that help reveal the message in this type of simple cipher. One is that an encrypted text message will be meaningless, which will be a strong indication that a cipher was used. Second, the letter frequencies that are widely known to exist in English—making E, T, A, O, and N the most common letters—are likely to help reveal some strong clues about the cipher used, if the message is of any length.
While the simple type of cipher described can be cracked and is no longer in serious use, there are more complex ones. With these ciphers as well as simple ones, the security of the encryption key is essential for the correct transmission of an encrypted message. Failure to obtain the key from the recipient means that the message will not be read. The encryption key that falls into the wrong hands destroys the security of the message. For this reason, encryption key management is an essential element of cryptography.
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