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The same key is used to both encrypt and decrypt communications in symmetric key cryptography, also known as symmetric encryption. A lot of governments and militaries have adopted this type of information encoding in recent years to ease covert communications. Symmetric key methods are now frequently used in many different kinds of computer systems to improve data security.
The foundation of symmetric encryption systems is a single key that is shared by two or more users. The message or piece of data that is being encoded is represented by the so-called plaintext, which is encrypted and decrypted using the same key. A plaintext (input) is encrypted by passing it through an encryption technique known as a cipher, which produces a ciphertext (output).
The only way to read or access the data contained in the ciphertext, if the encryption method is effective enough, is by employing the appropriate key to decrypt it. Decryption primarily involves transforming ciphertext into plaintext.
The safety of symmetric encryption systems depends on how challenging it is to brute force them by making random guesses at the matching key. For instance, it would take trillions of years for conventional computer technology to guess a 128-bit key. The difficulty of cracking an encryption key increases with its length. In general, 256-bit keys are thought to be extremely safe and, in theory, immune to brute force attacks by quantum computers.
Block and stream ciphers are the foundation of two of the most popular symmetric encryption techniques in use today. Block ciphers divide data into units of a predefined size, and each unit is then encrypted using the appropriate encryption method and key (for instance, 128-bit plaintext is converted into 128-bit ciphertext). On the other hand, stream ciphers only encrypt plaintext data in 1-bit increments (1-bit ciphertext is converted from 1-bit plaintext at a time), not in blocks.