Comparisons of Blowfish and Cast-128 Algorithms As Per Their Cryptography Strength and Encryption

COMPARISONS OF BLOWFISH AND CAST-128 ALGORITHMS AS PER THEIR CRYPTOGRAPHY STRENGTH AND ENCRYPTION

1HIRAL DESAI, 2SALOT PINAL, 3FIRDOS SHEIKH ALAM

1,2,3Pacific School of Engineering E-mail:1 [email protected], 2 [email protected], [email protected]

Abstract— Rapid growth of internet required the need for securing information from eavesdropper or attacker. Encryption algorithms pay vital role to secure information. Encryption algorithms involve the process of converting plaintext to cipher text(unreadable text) with using different key size. This paper demonstrates the introduction of well known symmetric ciphers Blowfish and cast-128 also provide the security and performance analysis of blowfish and cast-128 algorithms as per key size, Cryptography strength and the function that is use in blowfish and cast-128 algorithms.

Index Terms— Cipher Text, Eavesdropper, Encryption Algorithm, Plaintext, Key, Cryptographic Strength.

I. INTRODUCTION II. DETAIL FEISTEL STRUCTURE OF BLOWFISH AND CAST-128 ALGORITHMS Cryptography is the art and science of protecting information from unwanted person and converting Figure 2.1.1 Shows the structure of Blowfish it into a form undistinguishable by its attackers algorithm and Figure 2.2.1 shows the Sructure of though stored and transmitted. The main aim of Cast-128 algorithm. cryptography is keeping data secure form unauthorized persons. Data cryptography mostly is 2.1. Blowfish Encryption the scramble of the content of data, such as text The plaintext is divided into two 32-bit halves LE0 data, image related data and audio, video related and E0. data to compose the data illegible, imperceptible or Encryption Side:- unintelligible during communication or storage LE1= RE0 ⊕ F(LE0,P1) called Encryption process. The reverse of data RE1= LEO ⊕ P1 encryption process is called data Decryption. LE1= REO ⊕ F(RE1) Cryptography provides a number of security goals For i=1 to 16 round do to avoid a security issue. Due to security REi=LEi-1 ⊕ Pi advantages of cryptography it is widely used today. LEi=REi-1 ⊕ F(REi) LE17=RE16 ⊕ P18 Blowfish is a symmetric block cipher developed by RE17=LE16 ⊕ P17 bruce schneier in1993.Blowfish uses a feistel Blowfish uses two primitive operations: structure. It encrypts 64-bit blocks of plaintext. 1) Addition : Addition of words, denoted by +, Blowfish makes use of key 14 32-bit key.(14*32=448 2) Bitwise exclusive-OR : This operation is denoted bit).That key is used to generate 18 32-bit by ⊕. subkeys(18*32=576 bit).Blowfish takes 16 round.The The 32-bit input to F is divided into 4 byte. keys are stored in a K array k1,k2….kj (1,2,….14). 4 S-Box is used each takes 8 bit as a input and gives 32 The sub keys are stored in the P array bit output.Thus each round includes the complex use :P1,p2,….p18.There are four S-boxes used in blowfish of XOR plus substitution using S-boxes. each with 256 32-bit entries.

Total S-Box and P-array entry is 256*4=1024 So, 1024+18=1042 32-bit entry. CAST algorithms are introduce by Carlise Adams and Stafford Tavares. CAS-128 is a Symmetric encryption algorithm. CAST-128 uses a Feistel structure.64 bit block is input to the algorithm. Key size between 40 to 128 bits, in 8-bit increments(40,48,56,64…120,128).CAST-128 uses 12 or 16 round .For key size up to and including 80 bits , the algorithm uses 12 rounds instead of 16. For key sizes greater than 80 bits, the algorithm uses the full 16 round. Figure 2.1.1 : Structure of Blowfish encryption

Proceedings of 7th IRF International Conference, 30th October 2015, Hyderabad, India, ISBN: 978-93-85832-30-7 37 Comparisons of Blowfish and Cast-128 Algorithms as Per Their Cryptography Strength and Encryption 2.2. CAST-128 Encryption Table 3.1 describe the security features of Blowfish algorithm and Table 3.2 describe the security features of CAST-128 algorithm.

Table 3.1

Figure 2.2.1 : Structure of CAST-128 encryption

Figure 2.2.1 shows the structure of cast-128.Split the plaintext into left and right 32-bit halves. Compute 16 pairs of subkeys (kmi,kri) from K. .Four S-Box is used each takes 8 bit as a input and gives 32 bit output. The Function of S-box F consist modular addition and subtraction and XOR operations. F is of Type 1, Type 2, or Type 3, depending on i. Exchange final L16 and R16 and concate result to produce final cipher text.

Encryption Side: L1 = R0 Table 3.2 R1 = L0 ⊕ F(R0,kmi,kri) IV. COMPARISION OF ENCRYPTION TIME For i=1 to 16 round OF BLOWFISH AND CAST-128 Li = Ri-1 ALGORITHMS Ri = Li-1 ⊕ F(Ri-1,kmi,kri) If you are using Word, use either the Microsoft III. COMPARISION OF FIESTEL STRUCTURE Equation Editor or the MathType add-on OF BLOWFISH AND CAST-128 ALGORITHMS (http://www.mathtype.com) for equations in your paper (Insert | Object | Create New | Microsoft Blowfish and CAST-128 both algorithms are uses a Equation or MathType Equation). “Float over text” feistel structure,But have some different operations. should not be selected.

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Proceedings of 7th IRF International Conference, 30th October 2015, Hyderabad, India, ISBN: 978-93-85832-30-7 41