## More on RC4

Read the section on RC4 in this article. Try to mentally follow the steps for encryption with the algorithm. What are some of the strengths and weaknesses of RC4 as noted in this article?

The cryptographic techniques are broadly classified into different categories namely,

1. Symmetric Key Algorithm (Secret Key)

2. Asymmetric Key Algorithm (Public Key)

3. Hybrid Key Algorithm

1. #### Stream Cipher

A stream cipher is a method of encrypting plain text into cipher text. In this method, the cryptographic key and algorithm are applied to each binary digit in a data stream, one bit at a time.

Cryptography

01

01

Symmetric Ciphers

Stream Ciphers

Asymmetric Ciphers

Block Ciphers

Hybrid Ciphers

Figure 4.Principles of encrypting m bits with a stream

Stream Cipher

2. #### Block Cipher

A block cipher is one in which a block of plain text is treated as a whole and used to produce a cipher text block of equal length. A block size of 64 or 128 bit is used.

 C O M P U T E R

Figure 2. Main Areas within Cryptography

1. Symmetric Key Algorithm

Symmetric Key Algorithm is referred to as shared key encryption algorithm or secret key algorithm [3,4]. In this algorithm the sender and receiver (both the parties) uses the same key to encrypt or decrypt the data. The algorithm is further classified into Stream Cipher and Block Cipher. Symmetric Key Algorithm is extremely fast, and their relatively low complexity allows for easy implementation. Some Important symmetric key algorithms are DES, 3DES, AES, Blowfish, Twofish, Serpent, SEED, IDEA, RC2, RC4 and RC6.

Plain Text

Encryption Logic

Sender

Cipher Text

Encryption Algorithm

 j 6 b x # 8 o g

Figure 5. Block Cipher Encryption

2. Asymmetric Key Algorithm

Asymmetric Key Algorithm is also called Public Key Algorithm [3,4]. In this algorithm the sender and receiver uses two different keys namely Public Key and Private Key to encrypt and decrypt the data. The sender uses the receivers public key for encrypting the plain text into cipher text. The receiver uses his private key for decrypting the cipher text into plain text. The Private Key used in this Algorithm is always kept confidential. Asymmetric Key Algorithm is slow and impose high computational burden compared to Symmetric Key Algorithm. The most familiar asymmetric key algorithm is RSA. Other asymmetric key algorithms are Diffe_Hellman, DSA, EIGamal, ECDSA and XTR

Decryption Logic

Plain Text

Figure 3. Symmetric Key Algorithm

Table 1

Comparison of Symmetric Key Algorithms

 S. No Algorithm Key Length (bits) Rounds Created By Year 1. Advanced Encryption Standards (AES) 128, 192, 256 9,11,13 Joan Daemen & Vincent Rijmen 1998 2. Data Encryption Standards (DES) 56 16 IBM 1975 3. Triple Data Encryption Standards (3DES) 168 48 IBM 1978 4. Blowfish 32-448 (128 by default) 16 Bruce Schneier 1993
3. Hybrid Algorithm

In the modern cryptographic system the Symmetric Key Algorithm and Asymmetric Key Algorithm are used for the encryption and decryption process [3,4]. The Asymmetric Key Algorithms are used to distribute symmetric keys at the start session. Once a symmetric key is known to all parties of the session, faster symmetric key algorithms are used for the encryption and decryption process. This algorithm mainly simplifies the key distribution problem.

Plain Text

algorithms namely Rivest Cipher4 (RC4), Rivest Cipher5 (RC5) nd Rivest Cipher6 (RC6). Among them RC4 belong to the stream cipher category and the remaining two algorithms RC5 and RC6 are belong to the block cipher category which is shown in figure 7.

Symmetric Encryption Algorithms

Rons Cryptographic Algorithms

Sender

Encryption Logic

Decryption Logic

Cipher Text

Stream Cipher Block Cipher

RC4 RC5 RC6