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What Is Ciphertext?

Ciphertext has been used for military purposes since the time of Julius Caesar.
Messages can be encoded using ciphers, resulting in ciphertext.
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  • Written By: Mary Elizabeth
  • Edited By: Bronwyn Harris
  • Last Modified Date: 20 June 2014
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The word cipher has a specific and a general meaning. Cipher is used loosely to refer to any way of encoding a message. More specifically, a cipher is a cryptographic system in which an algorithm, or set of predetermined instructions or procedures, is used to substitute symbols or symbol groups for sections of text in order to make them indecipherable, that is, unreadable. The original material that a cipher is used on is called plaintext. The result, after it is enciphered or encrypted, is ciphertext.

Ciphertext has been used for military operations since the at least the time of Julius Caesar, and today is commonly used for messages sent over the Internet for security purposes. In order to send a message using ciphertext, the message first must be encrypted using a cipher key. When the message arrives at the address to which it was sent, it needs to be deciphered or decrypted to reveal the plaintext. Again, a cipher key is needed.

Caesar’s cipher was comparatively simple. It uses a plaintext alphabet which is just the usual alphabet — in Caesar’s time, it would have been the Latin alphabet; in our time, it can easily be visualized using any modern alphabet. The ciphertext alphabet is created by shifting D to the position usually held by A as the first letter and placing the first three letters at the end of the string like this:

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Plaintext: ABCDEFGHIJKLMNOPQRSTUVWXYZ

Ciphertext: DEFGHIJKLMNOPQRSTUVWXYZABC

Caesar’s generals simply had to substitute letter for letter in order to decipher what their emperor’s instructions.

Twenty-five different ciphers can be created by shifting the alphabet in this manner, but they are all simple ciphers. With only 25 possibilities, it only takes time to crack the cipher and have access to the ciphertext. In addition, frequently occurring words, like definite articles, could easily be picked out, knowledge of the letter frequencies of the language could be readily employed, and with this type of analysis used, there wouldn’t be a need to try many possibilities to find the right one.

The greater the size of the key, the stronger the cipher. For example, the Data Encryption Standard (DES), which was formerly used for Internet messages, had a key of only 56 bits. The replacement, Advanced Encryption Standard (AES), which was introduced in 2000 and employs the Rijndael algorithm, can use 128-bit, 192-bit, and 256-bit keys. AES is used in Symmetric-Key Encryption, one of the types of encryption used for Internet messages.

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Discuss this Article

eCleopatra
Post 5

The Code-Breakers - highly recommended to watch!

NathanG
Post 4

@miriam98 - I’m sure that a hardcore cracker or hacker or someone skilled in conducting a ciphertext attack could tell you for sure how secure your encryption is, but I would feel pretty safe.

I know that in the early days of the Internet you could download some very secure encryption software that would encrypt your stuff.

Apparently the software was so secure that the U.S. government had specific laws banning the export of the software to other countries (a difficult law to enforce, I would gather, given how easy it is to send stuff over the Internet).

The fact that such a law was in place tells me that the encryption algorithms must have been pretty good. They didn’t want it to get into enemy hands.

miriam98
Post 3

@Charred - I’ve heard that the 256-bit encryption algorithms for the ciphers are the highest form of encryption and the article seems to confirm that.

Anytime I go online and do some shopping I am always concerned about security. I don’t want somebody reading my credit card information or stuff like that.

When I go to the website, however, it informs me that it’s using the 256-bit encryption algorithm. While I’ve never understood everything that this entails (before reading this article) I thought it must be pretty important.

Now I know, and feel a little bit more secure doing online shopping.

Charred
Post 2

@MrMoody - That sounds like fun. At work we’ve done some programming with the Rijndael algorithm mentioned in the article. I have absolutely no idea how it works, except that it’s very, very secure.

That means it’s a tough code to break. We use it in some of our relay protection software. Relay technicians have to store information about their equipment into their software, and that information has to be secure.

Otherwise anyone could come along and damage their equipment. So our software uses that algorithm and stores it in the database, and then decrypts the information when the technician needs to read it again.

MrMoody
Post 1

I’ve played with cryptanalysis on my own, just for fun. As the article points out, you don’t have to be a programmer – Caesar wasn’t.

The principle is simple, and sometimes you find ciphers being used in word puzzles and things like that. The process is fun.

I do, however, work as a programmer so I know how to extend the process to programming as well. One time I wrote what I called a top-secret text editor, kind of like Windows Notepad.

However, Notepad is not encrypted. My top-secret text editor was. Every character that you typed in the editor was shifted by several characters. Every letter was shifted by four characters to the right – so ‘A’ became ‘E’ and so forth.

It was nothing fancy, and it’s certainly not the kind of algorithm you would use to keep military secrets, but I used it to store some personal information that I wanted hidden from prying eyes.

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