 Open Access
 Total Downloads : 203
 Authors : K. Sujatha, P. V. Nageswara Rao, A. Arjuna Rao, L. V. Rajesh
 Paper ID : IJERTV5IS020233
 Volume & Issue : Volume 05, Issue 02 (February 2016)
 DOI : http://dx.doi.org/10.17577/IJERTV5IS020233
 Published (First Online): 17022016
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Renowned Information Security Algorithms: A Comparative Study
K. Sujatha
Research Scholar,
GITAM University, Visakhapatnam
P V Nageswara Rao
Professor,
GITAM University, Visakhapatnam
A Arjuna Rao
Director and Principal,
Miracle Educational Society Group of Institutions, Vizianagram
L V Rajesh
Associate Professor,
Miracle Educational Society Group of Institutions, Vizianagram
Abstract : Authentication and Encryption with Key Exchange are the key concepts in Cryptography, which have been continuously being targeted. Many Security Algorithms are developed as research outcome and they are broadly classified into Symmetric and Asymmetric algorithms. Symmetric Algorithms are conventional which use a common secret key that is transmitted by using physical or other communication channel. Data Encryption Standard, Triple Data Encryption Algorithm, International Data Encryption Algorithm, Blowfish and AES are the algorithms that are categorized into Symmetric. In order to make key distribution easy, Asymmetric Key algorithms such as Rivest Shamir Adleman, Diffie Hellman, Elgamal, Digital Signature Algorithm and Elliptic Curve Cryptography, are used for Encryption and Authentication where secret key remains with generating user. Rivest Shamir Adleman, ElGamal and Elliptic Curve Cryptography are the most widely used public key algorithms that perform Key Exchange and used for both authentication and confidentiality. Digital Signature Algorithm is a generally applied digital signature system where as Diffie Hellman is used only for Key Exchange. This paper presents a review of the renowned Symmetric and Asymmetric algorithms. The specified algorithms are developed and test results are presented comparing the performance and key sizes.
Keywords: Authentication, Encryption, Symmetric Algorithms, Asymmetric Algorithms, Data Encryption Standard(DES), Triple Data Encryption Algorithm(TDEA), International Data Encryption Algorithm(IDEA), Blowfish and Advanced Encryption Standard(AES), Rivest Shamir Adleman (RSA), ElGamal, Elliptic Curve Cryptography(ECC), Digital Signature Algorithm(DSA).

INTRODUCTION
Encryption is the means of analytically modifying data to make it illegible to unauthorized users. Sender encrypts the Data which moves over the network in coded form. The computer at the receiving end then decrypts the data in order to read the message. Encryption methods have been around for centuries. The majority of computer encryption algorithms are outcome of the modifying operations of large prime numbers. The algorithms are intensely based on mathematics and Encryption techniques are used for ensuring confidentiality, integrity and authentication [1].
There are several encryption algorithms which are unique. Though they are strong to some extent there are flaws like some fail in confidentiality not resistant to existing attacks. Strength is ability of a cryptographic system to safeguard information from attack which depends on factors listed[2].

Secret key : maintaining secrecy in key

Key Search: difficulty in key guessing or using all possible keys.

Known plaintext Attack: Decrypt with some known plaintext.

Encryption Algorithm Breaking: Encryption algorithm is cracked without knowledge of the encryption key

Create New Techniques: Decrypt the encrypted file more easily without knowing the key.
To prove the strength of an algorithm, a mathematician has to show that the algorithm is challenging to specific type of attacks that earlier proved on other algorithms. However even an algorithm that is resistant to each known attack cannot considered to be secure, as new attacks are constantly being developed.


SYMMETRIC ENCRYPTION
Symmetric encryption is now and then called conventional encryption since it is the initially utilized before the improvement of public key systems. Symmetric encryption is most regularly utilized even now, albeit open key uneven encryption has recently gotten significant thought. The decoding procedure is the converse of the encryption process thus it is called as the symmetric encryption [1].
Fig 1: The symmetric encryption process.
Symmetric encryption/decryption process as shown in figure 1 follows the process as listed [2].

One key value known as secret key is made available jointly to the sending and receiving users who wish to communicate.

The sending user applies secret key on the encryption algorithm and encrypts the data to generate cipher text.

The cipher text is delivered to the target user.

The receiving user applies the same secret key on a decryption algorithm to decrypt the data to obtain the plaintext.
Symmetric encryption should be carefully executed and then it can be extremely secure. The most significant considerations for enhancing the security of any encryption scheme are as listed [2]:

The encryption algorithm strength

The key strength

The key secrecy
128bit key breaking might happen if the key is not kept to be sufficiently secure. The software system should offer some secure suggests that for delivering the key to the receiving laptop by mistreatment varied key delivery systems instead of sealed cover method of passing the key. If the secret key is derived, everything is disclosed. Periodic renewal of the secret key is done to beat this downside. The distinctive key utilized by a combine of human action computers could be make with each session or when a given quantity. Key renewal will increase the amount of keys crossing the network that compounds the requirement for effective key protection.
Several noted cryptography algorithms as shown in figure

a pair of create use of symmetric cryptography. the foremost illustrious symmetric algorithm could be the information cryptography customary (DES). DES is employed with many common cryptography techniques, together with Kerberos. DES uses a 56bit key, that several specialists say is simply too small. The DES algorithm was truly cracked through bruteforce techniques during a check work in 1998.
Triple DES (3DES) is that the common name for the Triple encoding algorithm or TDEA, a symmetrickey block cipher that applies the information cryptography DES cipher algorithm thrice to every data block. The Advanced cryptography customary or AES could be a symmetric block cipher utilized by the U.S. government to shield classified data and is enforced in software package and hardware throughout the globe to write in code sensitive knowledge. Different conventional cryptography algorithms embody the 128bit key plan algorithm. The Blowfish usually uses a 128bit key, though key length could vary to up to 448 bits.
Fig. 2: Renowned Symmetric Algorithms

Data Encryption Standard (DES)
DES designed by IBM was the first encryption standard to be published by NIST which is minor variation of Feistel network. Feistel cipher structure uses basically two operations, Substitution and Permutation. This has sixteen rounds and generates 16 subkeys from original key, one for each round [3]. The DES was initially considered as a strong algorithm and is most widely used, but today the large amount of data and short key length of DES limits its use. The DES key size is only 56 bits which is very short for proper security, as this can be bruteforced[4]. DES uses 64bit blocks that raise probable issues while encrypting huge amount of data with the same key. Encryption requires plaintext, P and key, K as input as shown in equation (1) generates ciphertext.
C = E(K, P) (1)
Decryption as shown in equation (2) uses ciphertext, C and Key, K as input, and generates plaintext, P, but uses subkeys Ki in reverse order[5].
P = D(K, P) (2)

TripleDES (3DES)
3DES was standardized to be used in 1985 however printed in 1999. 3DES was far more difficult version of DES achieving high level of security by encrypting the info exploitation DES 3 times exploitation with completely three different unrelated keys. 3DES remains approved to be used by U.S.A. governmental systems. 3DES is secure up to a minimum of 2168 security that is tough to interrupt as this uses a key length of 168 bits. However it is slow, particularly in package and hardware implementation is really crucial. The encoding operate follows encrypt decryptencrypt (EDE) sequence, with Plaintext, P, Ciphertext, C, and 3 distinct keys K1,K2,K3 with every key being fifty six bits, equation(3) shows this process[6].
C = E(K3, D(K2, E(K1, P))) (3)
Decryption is the same processed while applying keys in reverse order as in equation (4).
P = D(K1, E(K2, D(K3, C))) (4)
Multiple DES proposed by the authors of this paper uses DES encryption in random number of times and similarly decryption is also applied[7].

International Data Encryption Algorithm (IDEA)
James L. Massey and Xuejia Lai in 1990 developed an encryption algorithm named as International Data Encryption Algorithm[8]. This is quick, secure and impervious to both linear and differential analysis. This uses noninvertible hash function that does not use lookup tables or Sboxes and hence is one of secure block ciphers used in public domain. This utilize 52 subkeys, which are 16 bits long. The block of plaintext in IDEA is segmented of 16 bits length four quarters. In IDEA, three operations are utilized to merge two 16 bit values and generate a 16 bit result, with XOR, addition and multiplication[9].

Blowfish Algorithm
Bruce Schneier planned block cipher, Blowfish that is taken into account as a extremely rated secure encoding algorithm, with completely different structure and practicality than the opposite mentioned encoding algorithms[10]. Blowfish may be a quick, compact, and straightforward block encoding algorithm with variable length key permitting a tradeoff between speed and security. The block size is sixty four bit and uses 16round Feistel Cipher and enormous keydependent S boxes[11,12]. The algorithm keeps 2 subkey arrays; 18 entry Parray and 4 256entry Sboxes. The Sboxes settle for 8bit input and turn out 32bit output. One entry of the Parray is employed each spherical, and once the ultimate spherical, every half the info block is XORed with one amongst the 2 remaining unused Pentries[13,14].

Advanced Encryption Standard(AES)
Rijndael developed by Joan Daemen and Vincent Rijmen, is chosen as final AES algorithm in 1997 by NIST[15]. AES victimization variable key size is phenomenally fast and smaller cipher. Its centrosymmetric and parallel structure gives decent adaptability to implementers, with successful resistance against cryptological attacks. AES will be well uniquely designed to a decent fluctuate of recent processors such as Pentium, abridged instruction set parallel and computing processors. AES acknowledges keys of 128, 192 or 256 bits, and is prudent in every hardware[16]. This completely was chosen through associate open competition involving numerous cryptographers all through numerous years. This algorithmic rule procedures entire block in parallel and isn't a feistal structure. Each stage utilizes 3 substitutions and one permutation round. Substitution rounds square measure Substitute bytes, join columns and Add round key and permutation spherical is shift rows. There square measure ten rounds during this algorithmic standard [17].

Advantages and Disadvantages of Symmetric Algorithms
Symmetric algorithms are widely used due to the following advantages

Symmetric algorithms are much faster compared to asymmetric algorithms

Security of algorithm is dependent on the length of the key. Large key size makes the algorithm hard to break.

Uses less computing power.


The disadvantages of symmetric algorithms can be listed as follows.

Secure mechanism is required to deliver secret key confidentially.

Every pair of users needs a unique secret key. Multiuser sharing requires maintaining multiple keys.

Only confidentiality is provided but not authenticity as the key is shared.
3. ASYMMETRIC (PUBLIC KEY) ENCRYPTION
Public Key cryptography is an alternate approach that has emerged over the last twenty five years to unravel secret key distribution issues implicit with conventionally symmetrical cryptography. Asymmetric cryptography is named asymmetric as a result of the key wont to cipher the information is totally different from the key wont to rewrite the data[1]. This method is shown in figure 3.
Fig. 3: Asymmetric encryption process.
Asymmetric encryption is an encryption method identified as public key encryption. However in public key encryption, out of the two keys, the private key is held securely with a sender. The other key, the public key is made available to users that need to move data to the possessor of the private key. The steps are as follows [2]:

User A attempts to establish a communication channel with User B.

The user B produces a private key and a public key. The private key is not shared with anyone. The public key is made accessible to User A.

User A with the public key encrypts and transmits the data. The User B public key is stored on User A for future reference.

On receiving data User B decrypts it using the private key.
A significant side of public key strategies is that the coding performed through the general public key's a unidirectional operates. The general public key is accustomed encode the info, however solely the nonpublic key will decode the info once it's encrypted. Many renowned Asymmetric algorithms as listed in figure 4 supported Asymmetric coding [1].
Fig. 4: Renowned Asymmetric Algorithms

Diffie Hellman Key Exchange
DiffieHellman uses a combine of keys, public and personal however is employed for key exchanges that generate shared keys [18]. This algorithmic rule uses arithmetic modulus because the basis of its calculation. Suppose user A and user B follow this key exchange procedure with Eve acting as a person in middle fighter. Here are the calculation steps followed during this algorithmic rule that create certain that eve never gets to understand the ultimate keys through that actual cryptography of information takes place. First, a hard and fast modulus (n) and generator (g) are shared among communication users A and B and exploitation them several personal and public key pairs is generated. personal key of A and B are chosen as xA and xB are generated and public secret's computed exploitation the personal key as in equation (5) [19]
yA = gxB mod n
yB = gxA mod n – (5)
Then shared secret key, Key is generated at recipients end by user A and B, by using their private keys and senders public keys as shown in equation (6).
Key = yAxB mod n
Key = yBxA mod n – (6)
The result calculated using equations (8) and (9) produce identical result and hence a secret key is shared that can be used by symmetric algorithms [20,21].

RivestShamirAdleman (RSA) Algorithm
RSA is widely used in encryption and authentication using pair of keys, public and private. From each public key pair new modulus is generated. Public key algorithm invented in 1977 by Ron Rivest, Adi Shamir and Leonard Adleman(RSA) [22]. Te main operation of RSA is to compute modular exponentiation. Prime numbers generation gives good efficiency and strength to the algorithm. The cryptosystem based on RSA is on the assumption which factors large integers and computationally hard and mainly based on Primality Testing, Extended Euclidians algorithm, Modular Exponentiation [23]. In Decryption, more computation time and capacity are required. This is included as part of the Web browsers from Microsoft and Netscape. RSA is a publickey cryptography based algorithm that presumes factoring problem, which is the difficulty of factoring large integers. There are three steps involved in the RSA algorithm that are key generation, encryption and decryption. RSA keys are of a power of two, like 512, 1024, or 2048 bits length [24].
First, a couple of large primes p and q are selected randomly and using p and q, n and Ã˜ are calculated. n= p * q
Ã˜ = (p1)*(q1)
Exponent e is selected basing on n and private exponent d from e, p and q. Here, (n, e) is treated as the public key and (n, d) as the private key.The RSA encryption shown in equation (7) is the exponentiation tothe eth power modulo n
C = Me mod n – (7)
The decryption shown in equation (8) is performed as exponentiation to the dth power modulo n.
M = Cd mod n (8)

ElGamal
The ElGamal algorithmic rule could be a publickey cryptosystem supported the separate exponent downside. It consists of each the coding and signature algorithms [25]. The ElGamal signature algorithmic rule is comparable to the coding algorithmic rule in this the general public key and personal key have a similar kind. However, coding isn't a similar as signature verification and signature creation depends on the ElGamal signature algorithmic rule.
The mathematical constructs needed area unit Cyclic teams, standard mathematical operation resolution algorithms etc. the most disadvantages of ElGamal area unit the necessity for randomness, and its slower speed and also the message growth by an element of 2 takes place throughout coding [26]. However, such message growth is negligible if the cryptosystem is employed just for exchange of secret keys ElGamal coding is employed
within secure package, recent versions of PGP and alternative cryptosystems. ElGamal isn't semantically secure. ElGamal algorithms can't solely be utilized in encoding, however in digital signature and also the security depends on the matter of divergence exponent in finite domains[27].
Y = gx(mod p) (9)
The private key is x. G and p can be shared by a group of user. ElGamal encryption consists of three components, the key generator, the encryption algorithm, and the decryption algorithm.

Digital Signature Algorithm (DSA)
NIST proposed DSA in August 1991 for digital signatures to employ in their Digital Signature Standard [28]. The DSA is employed by a person to come up with a digital signature on knowledge and to verify the believability of the signature. This uses a combine of keys, private and public for implementing digital signatures. The nonpublic key's employed in the signature generation method and also the public key's employed in the signature verification method [29].
For signature generation and verification, the info that is spoken as a message, M, is reduced by suggests that of the Secure Hash algorithmic rule (SHA) laid out in FIPS. In alternative words, signatures cannot be cast. However, by mistreatment the signatory's public key, anyone will verify a properly signed message[30]. Here, the generation of a new stored modulus is not done every time. The public key is composed of two pieces: the public key (y) and the modulus data (p, q, and g) where modulus size is in between 512 and 2048 bits with 64 bits increment. The personal key (x) may be a random 160bit range. for each signature, a brand new 160bit k is made. Once the signature is made, k may be destroyed. what is more, the signature method creates r and s, they're utilized in the verification method to come up with v that is compared to r to verify a signature [31].
A means of associating public and personal key pairs to the corresponding users is needed. That is, there should be a binding of a user's identity and therefore the user's public key. This binding could also be certified by a reciprocally trustworthy party, for instance, a certifying authority might sign credentials containing a user's public key and identity to make a certificate. DSA is highly secure because of the difficulty of computing the discrete log. The goal is to find the smallest natural number x as shown in equation (10), after choosing a prime p and and that are nonnegative integers mod p, t.
x (mod p). (10)
The x is the number indicated by L(), the discrete log of with respect to . Generally, is considered to be a primitive root mod p. Also is a primitive root mod p if and only if {i mod p  0 i p2} = {1, 2, , p1} [32].

Elliptic Curve Cryptography (ECC)
ECC was discovered in 1985 by Victor Miller and Neil Koblitz severally, as another mechanism for implementing publickey cryptography[33,34]. Publickey algorithms produce a mechanism for sharing keys among massive numbers of participants or entities in a very advanced data system. Most publickey cryptosystems square measure engineered over arithmetic in finite fields which are algebraic structures that have addition and multiplication operations every with inverses. Error correction code builds a finite field out of the set of solutions to associate degree elliptic curve equation together with associate degree additive identity that corresponds to the purpose at infinity.
ECC is efficacious as a result of it's believed to be more durable to cipher, e.g., separate logs over the finite fields of code than within the underlying whole number finite fields. this implies that key sizes in code will be smaller than the corresponding key sizes in cryptosystems supported different fields. ECC is not, however, famed to be more durable than the other system [35].
ECC Challenge has opened a chance for folks round the world to form new ways of assaultive the formula and exposing any weaknesses. The ECC Challenge started in Nov 1997 and still runs today[36,37]. An Elliptic Curve is a curve given by the equation (11) which is in the form shown below is the main heart of this cryptography.
y2 = x3 + ax + b – (11)
{where = 4a3 + 27b2 is nonzero}
For maximum efficiency, a Koblitz curve is used with a=0 or a=1 shown in equation (12)
y2 + xy = x3 + ax2 + 1 (12)

Advantages and Disadvantages of Asymmetric Algorithms
The advantages of asymmetric algorithms listed are follows are the reasons for extensive usage.

Key distribution is better as secret key need not be shared

Provides both authenticity and confidentiality

Uses mathematical operations rather than bitwise operations and substitutions.

Ideally suit for real world applications. Public keys can be available and other key is safe with user.

The disadvantages of asymmetric algorithms are listed as follows.

Slower than symmetric algorithms as many of them involve Modular Exponentiation.

Complex in mathematical tasks.
4. RESULTS
The symmetric algorithms and asymmetric which are specified in sections 2 and 3 are thoroughly compared by using both literature survey and test results obtained after executing the various algorithms.
4.1 Symmetric Algorithms
The symmetric algorithms are developed and tested on sample data. The common features are summarized as listed in table 1 Table 1 : Salient Features of Renowned Symmetric Algorithms
Algorithm 
DES 
TDEA (Triple DES) 
IDEA 
BLOWFISH 
AES 
Proposed Year 
1975 
1985 
1990 
1993 
1997 
Proposed By 
IBM 
IBM 
James L. Massey, Xuejia Lai 
Bruce Schneier 
Joan Daemen, Vincent Rijmen 
Structure 
Feistal Structure 
Feistal Structure 
LaiMassey scheme. 
Feistal Structure 
Not Feistal structure 
Way of processing plaintext 
Block Cipher 
Block Cipher 
Block Cipher 
Block Cipher 
Block Cipher 
Plaintext Block Length 
64 bits 
64 bits 
64 bits 
64 bits 
128 bits 
Key Length 
56 bits 
168 or 112 bits 
128 bits 
Variable key length from 32 to 448 bits 
128, 192 or 256 bits 
Number of Rounds 
16 
16*3 
8 
16 
10 
Security Level 
Low 
Medium 
High 
16 
High 
Sample data of with varying sizes is taken and test results with the symmetric algorithms are drafted as in figure 5 and 6. Figure 5 shows the system mean time and follows figure 6 that shows the speedup ratio.
Fig. 5: Compare system mean time of symmetric algorithms with different inputs.
3.2 Asymmetric Algorithms
Fig. 6: Compare speedup ratio of symmetric algorithms with different inputs.
Similarly, the asymmetric algorithms are developed and tested on sample data. The most common features of asymmetric algorithms are as listed in table 2.
Table 2 : Salient Features of Renowned Asymmetric Algorithms
Algorithm 
DH 
RSA 
ElGamal 
DSA 
ECC 
Proposed Year 
1976 
1977 
1985 
1991 
1985 
Proposed By 
Whitfield Diffie, Martin E. Hellman 
Ron Rivest, Adi Shamir, Leonard Adleman 
Taher Elgamal 
David Kravitz 
Neal Koblitz, Victor Miller 
Mathematical Construct used 
modular exponentiation 
modular exponentiation 
modular exponentiation 
Approved Hash Function 
Elliptic Curve 
Plaintext Block Length 
– 
Variable 
Variable 
– 
Variable 
Key Length 
5122048 bits 
5122048 bits (bit length of RSA modulus n) 
Variable 
Length of parameter q in bits 
Order of base point of elliptic curve; bit length of n 
Usage 
Key Exchange 
Encryption & Signature 
Encryption & Signature 
Digital Signature 
Encryption & Signature 
However as shown in table 2 the purpose of PKC algorithm varies, but the common factor is key generation. Secure key size of the specified PKC algorithms are as listed in table 3.
Table 3: Application based Secure Key size for Renowed PKC Algorithms
Algorithm 
Simple Applications 
Moderate Applications 
Highly Secured Applications 
Near Future Applications 
DH 
768 
2048 
3072 
15424 
RSA 
768 
2048 
3072 
15424 
ElGamal 
768 
2048 
3072 
15424 
DSA 
768 
2048 
3072 
15424 
ECC 
128 
224 
256 
512 
The analysis of asymmetric algorithms on different applications basing on key size is shown in figure 7.
Fig. 7: Analysis of Asymmetric algorithms on different applications
The analysis shows that elliptic curve cryptography uses low key size comparative to all other comparable public key cryptographic algorithms. This is liable to any kind of application starting from simple to Highly Secured applications.
4. CONCLUSION
This paper presents the review of all the renowned Symmetric and Asymmetric Information Security Algorithms which are popular from past four decades. Symmetric algorithms are easy to develop and can be used by simple applications; however the key has to be shared secretly. Asymmetric algorithms overcome this problem by keeping the secret key with sender and sharing the secret key. The comparative analysis is given comparing all the specified algorithms and results specify that Elliptic Curve Cryptography is preferable in usage as this requires less key size though it involves complexity in mathematics compared to its neighboring algorithms.
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