# Chaotic Image Encryption: State-of-the-Art, Ecosystem, and Future Roadmap
## 3 State-of-the-Art
### State-of-the-Art in the Encryption Aspect
#### 3.3.2 Block Cipher vs. Stream Cipher  
Block and stream ciphers, although common with arbitrary binary encryption, typically fall short when encrypting images. However, when paired with sufficient chaos, they can be used effectively. Some block ciphers used in chaotic image encryption are studied below:  
* [PERSON] et al. [116] proposed a block cipher using the Blowfish algorithm and cross-chaos map. Cryptanalysis results showed strong security.
* Ecliptic Curve Cryptography (ECC) [PERSON] et al. [117] proposed an Ecliptic-Curve (EC)-based algorithm that utilizes pixel-level parallelism for faster encryption speeds. A different proposal by [PERSON] and [PERSON] et al. [118] uses ECC combined with the Hill cipher and Arnold cat map to achieve a strong encryption algorithm targeted at medical images.
* El-Gamal is a type of EC commonly utilized in cryptography. For example, [PERSON] et al. [119] proposed a public-key-based image encryption algorithm utilizing the El-Gamal EC to address common issues with key management. In another proposal by [PERSON] et al. [118], El-Gamal was used to encrypt images that were first permutated using zigzag and spiral scanning.
* [PERSON] and [PERSON] [120] proposed a novel technique of using images as the key to encrypt/decrypt a directory in a file system. This technique employs both AES and Rijideal ciphers, and evaluation results demonstrated its effectiveness.
* Rivest-Shamir-Adleman Cryptosystem (RSA) [PERSON] et al. [121] developed a novel asymmetric image encryption algorithm using RSA to solve the issue of key management. This algorithm uses the RSA key pairs to encrypt the initial values and parameters of the chaotic function so that the public key can encrypt images and only the private key can decrypt.
* Data Encryption Standard (DES) [PERSON] et al. [122] proposed an image encryption algorithm utilizing the logistic chaos sequence for chaotic sequence generation and an improved DES algorithm for encryption. Simulation results demonstrated good security and speed, making it suitable for real-time use.
* Novel block ciphers [PERSON] et al. [123] proposed a novel block cipher using two keys where the image is split into four blocks; each is encrypted n times, and finally, the keys are inverted and the blocks further encrypted m more times. Evaluation through standard tests demonstrated strong cryptographic properties, making the algorithm usable for real-time connections.  
[PERSON] and [PERSON] [124] proposed a novel stream cipher using a modified RC4 algorithm. The algorithm converts the image into three vectors for each color channel and uses the modified RC4 stream algorithm to encrypt them. Another algorithm utilizing the RC4 stream cipher was proposed by [PERSON] and [PERSON] [125]. This algorithm uses the logistic map to generate a keystream for encryption. The algorithm is lossless, which was verified by comparing the hash values of the image before encryption and the image after encrypting, then decrypting.
* Hybrid ciphers A hybrid approach utilizing both block and stream ciphers was proposed by [PERSON] and [PERSON] [126]. This algorithm splits the image into two sub-images and encrypts one using the block cipher and the other using the stream ciphers. The encrypted sub-images are then merged back together to form the final image. The use of two different types of ciphers greatly increases the complexity of the algorithm, leading to stronger cryptographic properties.