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,

Symmetric Key Algorithm (Secret Key)

Asymmetric Key Algorithm (Public Key)

Hybrid Key Algorithm

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

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
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M
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U
T
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R
Figure 2. Main Areas within Cryptography

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

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
Receiver
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
32448
(128 by default)
16
Bruce Schneier
1993

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
Receivers Public Key
Decryption Logic
Receivers Private Key
Cipher Text
Stream Cipher Block Cipher
RC4 RC5 RC6
Receiver
Plain Text
Figure 7. Ron's Cryptographic Algorithms
4.1. Rivest Cipher4 (RC4)
RC4 is a stream cipher from RSA Data Security. It
Figure 6. Asymmetric Key Algorithm
