# Analysis Of Symmetric Block Cipher Encryption Algorithms Computer Science Essay

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Security of data has been receiving increasing attention. Cryptography plays a crucial role in encoding data for transmission over unsecure mediums. A comparative study of the encryption algorithms is necessary as they consume a significant amount of computing resources. This paper presents a comparative study between four different symmetric block-cipher encryption algorithms AES, DES, 3DES and BLOWFISH; analysing their individual throughput, encryption speed on different OS environments and the time they consume for encrypting different data.

Keywords: Advanced Encryption Standard, Block-cipher encryption, Data Encryption Standard, Triple Data Encryption Standard,

## 1 Introduction

There are two basic techniques for encrypting information: Symmetric key encryption (also called secret key encryption) and Asymmetric key encryption (also called public key encryption). In symmetric key encryption same key is used for both encryption and decryption while in asymmetric key encryption different key is used. Symmetric ciphers can be divided into stream ciphers and block ciphers. While stream ciphers encrypt a single bit of plain text at a time block ciphers take a number of bits and encrypt them as a single unit.

## 2 Overview of algorithms

In this section we provide an overview of the four encryption algorithms on which our study is based.

## 2.1 DES

The Data Encryption Standard was a predominant algorithm for encryption of electronic data. It was highly influential in the advancement of modern cryptography. DES is now considered to be insecure for many applications chiefly due to the 56 bit key size being too small. DES uses a feistel network principle for encryption process.

## 2.2 3DES

The triple DES applies DES cipher algorithm three times to each block. It provides a relatively simple method of increasing the key size of DES to protect against brute force attacks made feasible by increasing computational power, without the need to design a completely new block cipher algorithm. 3DES like DES also uses the feistel network.

## 2.3 AES

The AES is a specification for encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. It was originally named Rijndael by the two cryptographers who developed it and submitted the algorithm to the AES selection process. The AES uses substitution-permutation network principle for its encryption process.

## 2.4 BLOWFISH

BLOWFISH was designed as a general purpose algorithm by Bruce Schneier. He intended it to be an alternative to the ageing DES and is free of problems and constraints associated with other algorithms. The algorithm is available in public domain and is unpatented. It provides a good encryption rate in software and no effective cryptanalysis of it has been found yet.

## 3.1 Features

Table 1: Features of the four algorithms

Factors

AES

3DES

DES

BLOWFISH

Key length

128,192,256 bits

(k1,k2,k3)168 bits

(k1=k2)112 bits

56 bits

32-448 bits

Cipher type

Symmetric block cipher

Symmetric block cipher

Symmetric block cipher

Symmetric block cipher

Block size

128,192,256 bits

64 bits

64 bits

64 bits

Developed in

2000

1978

1977

1993

Cryptanalysis

resistance

Strong against differential, truncated differential, linear, interpolation and square attacks

Vulnerable to differential, brute force attacker could analyse plain text using differential cryptanalysis

Vulnerable to differential and linear cryptanalysis; weak substitution tables

4 rounds of blowfish susceptible to a second order differential attack

Security

Considered secure

One only weak which is exit in DES

Considered secure

Possible keys

2128, 2192, 2256

2112, 2168

256

232-2448

Structure

Substitution- permutation network(10, 12 or 14 rounds)

Balanced Feistel network(16 rounds)

Feistel network(48 DES equivalent rounds)

Feistel network(16 rounds)

From the table we see that the DES and the 3DES algorithm are no longer considered secure and are no longer used in most of its previous applications.

3.2 Throughput

In the case of encryption throughput is calculated as the average of total plain text in k-bytes divided by the average encryption time and in the case of decryption throughput is calculated as the average of total cipher text divided by total decryption time. An experimental study with a laptop of 2.2GHz CPU 4GB RAM Core 2 Duo processor and Windows 7 Home Premium (32-bit) shows the following results. In this experiment software encrypts the text file size that ranges from 20Kb to 99000Kb.

Figure 1: Encryption Process Figure 2: Decryption Process

The graph above shows the throughput (in Mb/s) of different algorithms for both the encryption and decryption process. From the graph we see that the throughput for DES and 3DES is less. Furthermore, from the table we see that both the algorithms are proven inadequate. The result shows the superiority of blowfish algorithm over other algorithms in terms of throughput. The second point that can be inferred here is that AES has advantage over DES and 3DES.

## 3.3 Encryption speed on different OS environments

To calculate the encryption speeds, we use 3 laptops of 32-bit configuration:

Intel Pentium Dual Core with Windows XP

Intel Pentium Dual Core with Windows Vista

Intel Pentium Dual Core with Windows 7

Encrypting 16 text files of size ranging between 500Kb to 50Mb, the mean execution speed in Mb/s was calculated using the encryption time.

Table 2: Encryption Speed (Mb/s) of BLOWFISH and AES on different OS for text data

## Win 7

Blowfish

18.3

15.1

11.1

AES

14.2

12.4

11.3

Encrypting 16 text files of size ranging between 20Kb to 200Kb, the mean execution speed in Mb/s was calculated using the encryption time.

Table 3: Encryption Speed (Mb/s) of BLOWFISH and AES on different OS for image data

## Win 7

Blowfish

12.3

10.8

10.1

AES

6.7

4.8

4.3

It can be observed from the above information that both the algorithms run faster on Win XP. For image data BLOWFISH encrypts images more efficiently across all the three platforms.

## 4 Conclusion and future scope

This paper presents a comparative study of different symmetric block-cipher encryption algorithms. The four algorithms considered were AES, DES, 3DES and BLOWFISH; analysing their throughput and performance on different platforms. Firstly, it was concluded that the DES and the 3DES are no longer secure. Secondly, we inferred that BLOWFISH has a better throughput as compared to the AES. Third, it was seen that both BLOWFISH and AES ran faster on Win XP, with BLOWFISH encrypting images more efficiently.

In future, good features of both BLOWFISH and AES can be incorporated into a single algorithm which can perform well across all the platforms.