Abstract— This paper describes the results of efficient measuring methods whereby the encryption capability of four algorithms are evaluated. Specifically this work focuses on measuring the encryption quality, the memory requirement and the execution time of the encryption as an indicator to the usage of the software and the hardware. Also, the security analysis of these schemes is investigated from cryptographic viewpoint; statistical and differential attacks. A number of requirements are therefore identified upon which the algorithms are evaluated. The results of the efficient measuring methods show that each algorithm has its own strengths and weaknesses and no single encryption mechanism is able to get the maximum security with minimum execution time. The paper proposes that it may be possible to develop new algorithms providing adequate means of efficiency with acceptable security. Index Terms— Efficiency, Encryption, Image, Security. I. INTRODUCTION A digital image is defined as a two dimensional rectangle array. The elements of this array are denoted as pixels. Each pixel has an intensity value (digital number) and a location address (row, column). Many image data security solutions have been proposed in recent years. Encryption is one of these important common tools. Traditional encryption technique such as Data Encryption Standard (DES) treats the image data as the traditional text data, while image encryption uses special image data structure which leads to get efficiency of encryption with minimum requirement of encryption time [1], [2]. Encryption process transforms plain-image data into cipher-image through involving an algorithm for combining the original image with one or more keys. Techniques that use the same secret key for encryption and decryption are grouped under private key techniques [3], [4]. While, asymmetric key techniques use two different keys; public key for encryption and private key for decryption [5]. With wide usage of images in various applications, it is important to protect the confidential image using encryption Manuscript received March 18, 2008. Marwa Abd El-Wahed is a supervisor of quality control department in the International Group for Legal Consultation (IGLC) and Master of Science student in the Institute of Graduate Studies and Research, Department of Information Technology, Alexandria University, Egypt (e- mail: marwa2004_mm@yahoo.com). Saleh Mesbah is an Assistant Professor in the Department of Information Technology, Alexandria University, Egypt (e-mail: saleh.mesbah@gmail.com). Amin Shoukry is a Professor of Computer and Systems Engineering in the Faculty of Engineering, Alexandria University, Egypt (e-mail: amin.shoukry@gmail.com). techniques. Many works on image encryption techniques have been published as an attempt to develop more efficient performance and for enhancing security of cryptosystem. Considering that it is not significant to achieve secure cryptosystem with performance consuming. So, it will not be accepted by both practitioners and cryptanalysts. From the cryptographical point of view, a strong cryptosystem should be secure enough against all kinds of attacks that try to break the system such as known-plaintext attack, ciphertext-only attack, brute-force attack, statistical attack, and differential attack [6]. This paper explores the security analysis which has been performed on the proposed image encryption schemes (statistical and differential attacks), that demonstrates how much scheme is a satisfactory security. Also, evaluates efficiency by measuring the encryption quality, the memory requirement, and the execution time of the encryption. The rest of this paper is organized as follows. Section II provides a description of the selected image encryption algorithms. The efficient measuring methods and security analysis are presented in section III. This is followed by the experimental results in section IV. Finally, the concluding notes are introduced in section V. II. ENCRYPTION TECHNIQUES Image encryption algorithms can become an integral part of the image delivery process if they aim towards efficiency and at the same time preserve the highest security level. The following subsections describe briefly four symmetric image encryption algorithms. These algorithms can be classified into three techniques: transposition, substitution, and transposition - substitution techniques. A. Transposition Techniques (Position Permutation) Transposition means rearranging elements in the plain- image. Mitra et al. (2006) have used a random combinational of bit, pixel, and block permutations [3]. The permutation of bits decreases the perceptual information, whereas the permutation of pixels and blocks produce high level security. In the bit permutation technique, the bits in each pixel are permuted using the permutation keys with the key length equal to 8 (as the number of bits in each pixel). The number of permutations is = 8! = 40320 and the number of keys are 121. In the pixel permutation, 8 pixels are taken as a group and permuted with the same size key. The block size is (8 × 8) then it is difficult to decrypt. To extract the image, a combinational sequence of permutations and the permutation keys using pseudo random index generators should be known. In this investigation the combination of Efficiency and Security of Some Image Encryption Algorithms Marwa Abd El-Wahed, Saleh Mesbah, and Amin Shoukry Proceedings of the World Congress on Engineering 2008 Vol I WCE 2008, July 2 - 4, 2008, London, U.K. ISBN:978-988-98671-9-5 WCE 2008