**1. Introduction**

Cryptography is a practice and study of techniques of hidden data transfer so that only the intended receivers can extract and read the data [1]. It is the study of mathematical methods related to different aspects of informational security such as data origin, entity authentication, data integrity and confidentiality. The source data, which is to be protected by cryptography, is called plaintext. The procedure of transforming plaintext into an unreadable form termed ciphertext is called encryption. Decryption is the reverse process, recovering the plaintext back from a ciphertext. A cryptographic system is a set of algorithms, seeded by key that encrypt given messages into ciphertext and recover them back into input data. The scheme for a secret key encryption is first proposed by Shannon [2].

There are two categories of key-based cryptographic algorithms: *symmetric key* (secret key) cryptography and *public key* (asymmetric key) cryptography. In the first category, a sender and recipient share a private key known only to both of them. The same key is used for encryption and decryption. The most commonly used symmetric algorithms are AES (Advanced Encryption Standard) [3], Cha Cha [4], Blowfish [5], and IDEA (International Data Encryption Algorithm) [6]. By contrast, for asymmetric key cryptography, two keys are used: the first one is made publicly available to senders for encrypting plaintext while the second key is kept secret and is used by the receivers for decrypting the ciphertext. The most ordinarily exploited asymmetric schemes are the Rivest–Shamir–Adleman (RSA) cryptosystem [7] and ECC (Elliptic-curve cryptography) [8]. Symmetric encryption schemes are usually faster than public key counterparts and thus are preferred for encrypting big data.

In symmetric key cryptography, either *stream ciphers* or *block ciphers* can be used. An example of stream cipher is the Vigenere Cipher. These types of ciphers encrypt the letters or digits (typically bytes) of a message one at a time, while block ciphers take a number of bits and encrypt them as a single unit. Until now, many symmetric data encryption algorithms have been proposed. Some of them use classical schemes for text encryption. In [9], an extension of a public key cryptographic scheme to support a private key cryptographic scheme which is a mix of AES and ECC is presented. Plain text encryption based on AES, Blowfish, and SALSA20 is designed and experimentally evaluated in [10].

Some of them use chaotic equations for text encryption. In Reference [11], a novel scheme for digital image encryption based on a mix of chaos theory and DNA calculation is presented. In [12], a chaos-based pseudorandom generation scheme based on a six-dimensional chaotic system is proposed. A text encryption architecture is given. Novel symmetric data encryption algorithms based on logistic chaotic formula are presented in [13–15]. A chaotic logistic map filtered with binary function is proposed to text encryption scheme in Reference [16]. In [17], a chaos-based encryption technique based on logistic, pinchers, and sine-circle maps is proposed. An algorithm of chaotic data encryption system by using private characteristic of electrocardiogram (ECG) signal and logistic map is designed in [18]. In [19,20], the chaotic behaviour of a Chua system is used in novel text encryption scheme designs. A novel pseudorandom bit generation scheme based on rotation equations is proposed in [21]. The technique has good statistical properties measured by test packages. A novel encryption method based on modified pulsed-coupled spiking neurons circuit is presented in Reference [22]. In [23], a modified quadratic map for numeric sensor data encryption is proposed.
