What is Stream Cipher in Information Security?

A stream cipher encrypts a continuous string of binary numbers by using timevarying transformations on plaintext information. Therefore, this kind of encryption operates bit-by-bit, using keystreams to create ciphertext for arbitrary lengths of plain text messages.

The cipher combines a key (128/256 bits) and a nonce digit (64-128 bits) to create the keystream and a pseudorandom number XORed with the plaintext to create ciphertext.

While the key and the nonce can be reutilized, the keystream has to be unique for each encryption redundancy to provide security. Stream encryption ciphers implement this using feedback shift registers to make a unique nonce (number used only once) to produce the keystream.

Encryption schemes that need stream ciphers are less likely to propagate systemwide errors because an error in the translation of one bit does not generally influence the complete plaintext block.

Stream encryption also appears in a linear, continuous manner, creating it simpler and faster to perform. In the other terms, stream ciphers lack diffusion because each plaintext digit is mapped to one ciphertext output.

Moreover, they do not verify authenticity, and creating them vulnerable to insertions. If hackers divide the encryption algorithm, they can add or change the encrypted message without detection.

Stream ciphers are generally used to encrypt information in applications where the amount of plain text cannot be decided and in low latency use-methods. Stream ciphers create use of something known as keystream.

A keystream is a random 8-bit output that is produced by supplying a key to a pseudorandom bit generator. The 8-bit output created is known as keystream and is used in the encryption and decryption of information in a given stream cipher algorithm.

The bit-stream generator should be performed as an algorithmic process, so that the cryptographic bit stream can be created by both users.

In this method, the bit-stream generator is a key-controlled algorithm and should create a bit stream that is cryptographically powerful. Now, the two users required only share the generating key, and each can create the key stream.

Advantage of Stream Cipher

  • With a properly designed pseudorandom number generator, a stream cipher can be as safe as a block cipher of equal key length.

  • The main advantage of a stream cipher is that stream ciphers that do not use block ciphers as a constructing block are usually faster and use far less code than do block ciphers.

  • For applications that needed encryption/decryption of a stream of data, including over a data communications channel or a browser/Web link, a stream cipher can be the superior alternative.

  • For applications that manage with blocks of information, including file transfer, e-mail, and database, block ciphers can be more suitable.

  • However, this type of cipher can be utilized in essentially any application.