A cipher is a cryptographic system that substitutes symbols for text to make it unreadable. Ciphertext has been used for military operations and internet security. Caesar’s cipher was simple, but easily cracked. The larger the key size, the stronger the cipher. AES is commonly used for internet messages.
The word digit 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 groups of symbols for sections of text so as to make them undecipherable, i.e., unreadable. The source material on which a cipher is used is called the plaintext. The result, after it has been enciphered or scrambled, is the ciphertext.
Ciphertext has been used for military operations since at least the time of Julius Caesar and is commonly used today for messages sent over the Internet for security purposes. To send a message using ciphertext, the message must first be encrypted using an encryption key. When the message arrives at the address it was sent to, it needs to be decrypted or decrypted to reveal the plaintext. Again, an encryption key is required.
Caesar’s cipher was relatively simple. It uses a plaintext alphabet which is just the usual alphabet – in Caesar’s day, it would have been the Latin alphabet; in our time, it can be easily displayed using any modern alphabet. The ciphertext alphabet is created by moving 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:
Plaintext: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Ciphertext: DEFGHIJKLMNOPQRSTUVWXYZABC
Caesar’s generals simply had to substitute letter for letter to decipher what their emperor’s instructions were.
You can make twenty-five different digits by shifting the alphabet like this, but they’re all plain digits. With only 25 possibilities, it only takes time to crack the code and gain access to the ciphertext. Also, frequently occurring words, such as definite articles, could be easily spotted, knowledge of the letter frequencies of the language could be easily employed, and with this type of analysis used, there would be no need to try many possibilities to find the right one. .
The larger the key size, the stronger the cipher. For example, the Data Encryption Standard (DES), previously used for Internet messages, had a key size of only 56 bits. The replacement, Advanced Encryption Standard (AES), which was introduced in 2000 and uses the Rijndael algorithm, can use 128-bit, 192-bit and 256-bit keys. AES is used in symmetric key cryptography, one of the types of encryption used for Internet messages.
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