What are the Symmetric Key Cryptography in information security?

Symmetric key cryptography is a type of encryption scheme in which the similar key is used both to encrypt and decrypt messages. Such an approach of encoding data has been largely used in the previous decades to facilitate secret communication between governments and militaries.

Symmetric-key cryptography is called a shared-key, secret-key, single-key, one-key and eventually private-key cryptography. With this form of cryptography, it is clear that the key should be known to both the sender and the receiver that the shared. The complexity with this approach is the distribution of the key.

Symmetric key cryptography schemes are usually categorized such as stream ciphers or block ciphers. Stream ciphers work on a single bit (byte or computer word) at a time and execute some form of feedback structure so that the key is repeatedly changing.

A block cipher is so-called because the scheme encrypts one block of information at a time utilizing the same key on each block. In general, the same plaintext block will continually encrypt to the same ciphertext when using the similar key in a block cipher whereas the same plaintext will encrypt to different ciphertext in a stream cipher.

Block ciphers can operate in one of several modes which are as follows −

  • Electronic Codebook (ECB) mode is the simplest application and the shared key can be used to encrypt the plaintext block to form a ciphertext block. There are two identical plaintext blocks will always create the same ciphertext block. Although this is the most common mode of block ciphers, it is affected to multiple brute-force attacks.

  • Cipher Block Chaining (CBC) mode insert a feedback structure to the encryption scheme. In CBC, the plaintext is exclusively-ORed (XORed) with the prior ciphertext block prior to encryption. In this mode, there are two identical blocks of plaintext not encrypt to the similar ciphertext.

  • Cipher Feedback (CFB) mode is a block cipher implementation as a selfsynchronizing stream cipher. CFB mode enable data to be encrypted in units lower than the block size, which can be beneficial in some applications including encrypting interactive terminal input. If it is using 1-byte CFB mode.

    Each incoming character is located into a shift register the similar size as the block, encrypted, and the block transmitted. At the receiving side, the ciphertext is decrypted and the more bits in the block are discarded.

  • Output Feedback (OFB) mode is a block cipher implementation conceptually same to a synchronous stream cipher. OFB avoids the similar plaintext block from making the same ciphertext block by using an internal feedback structure that is independent of both the plaintext and ciphertext bitstreams.