As we exchange data over the Internet, it is imperative to protect our confidential information. Cryptographic algorithms such as AES and RC4 are used to restore data security.

Cryptologists have developed this effective algorithm that is challenging for a cryptanalyst by combining concepts from mathematics with computer science.

## Key Takeaways

- Advanced Encryption Standard (AES) is a symmetric encryption algorithm, whereas RC4 is a stream cipher algorithm.
- AES is widely adopted and considered more secure due to its block cipher structure and key lengths of 128, 192, or 256 bits.
- RC4, although faster, has known vulnerabilities and is no longer recommended for secure communications.

**AES vs RC4**

The difference between AES and RC4 is that AES is a block cipher, while RC4 is a stream cipher. Block encryption and stream encryption are symmetric algorithm classifications. A block cipher encodes plain text in block sizes, while a stream cipher encodes bit by bit, similar to a stream’s flow.

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AES, or Advanced Encryption Standard, was started in 1997 by the US National Institute of Standards and Technology (NIST) with incoming attacks on DES. The best encryption candidate.

Was selected from among fifteen other algorithms entered in an open competition to meet AES specifications. AES incorporates a 128-bit block.

And makes use of 3 specific key lengths: 128, 192, and 256 bits. RC4, or Rivest Cipher 4, was invented by Ron Rivest in 1987.

He developed it for RSA security. It is a symmetric stream cipher that encodes plaintext bit by bit with a key to convert it to ciphertext. Key sizes consist of 64-bit or 128-bit.

Originally, RC4 remained a secret until it was released to the public. Ron’s code is his other name.

**Comparison Table**

Parameters of comparison | AES | RC4 |
---|---|---|

Definition | Advanced Encryption Standard is a symmetric block cipher. | Rivest Cipher 4 is a symmetric stream cipher. |

Origin | AES was developed via an open competition in 1997. | Ron Rivest developed RC4 in 1987. |

Security | AES is more secure than RC4. | RC4 is not as secure as AES. |

Key sizes | 128, 192, and 256 bits | 64 or 128 bits |

Applications | SSL, TSL, etc. | NASA, NIST, etc. |

**What is AES?**

In 1997, the National Institute of Standards and Technology (NIST) held an open competition. Cryptologists from different parts of the world were invited to present their algorithms.

They had to meet the standards set in AES. Each of the algorithms was analyzed to find the most suitable one in 1999, and Rijndael was finally the chosen candidate.

AES is a block cipher that uses a symmetric key. The plain text entered is encoded in block sizes to convert it to ciphertext.

The bit size is limited to 128 bits, and key sizes of 128, 192, and 256 bits are used. Rounding varies depending on the size of the key.

There are 10 rounds for 128 bits, 12 for 192, and 14 for 256 bits. They are called AES128, AES192, and AES256.

The encryption process goes through four steps in each round. The more rounds, the more difficult the encryption code becomes to crack.

A symmetric key is used, which implies a unique key that is implemented by both the user and the recipient.

Some high-security conditions were established by NIST as follows:

- It must be a block cipher using a symmetric key.
- AES must have flexible key lengths.
- AES must be built in such a way that it can be integrated into both hardware and software.
- AES must be defined by the public.

**What is RC4?**

In 1987, Ron Rivest invented Rivest Cipher 4. He advanced it to steady RSA security.

A one-time pad inspired the initial concept, additionally referred to as the Verman cipher. Like AES, RC4 is also a symmetric algorithm unlike AES, RC4 is a stream cipher.

The encryption of Rivest Cipher 4 was kept secret until the code was released in 1994 in the public domain. RC4 is a stream cipher that is byte-oriented.

Encrypt the data bit by bit. Contains 64-bit or 128-bit key sizes. The encryption process involves a secret key that runs on the RC4 algorithm to generate the ciphertext.

In RC4, KSA and PRGA generate the keystream. KSA stands for Key Scheduling Algorithm, and PRGA stands for Pseudo-Random Generation Algorithm.

We use a single keystream (XOR) that combines the permutation of 256 probable bytes and a pair of 8-bit index pointers. Likewise, decryption follows a similar XOR pattern.

Various applications of RC4 are

- SSL (1995)
- WEP (1997)
- TLS (1999)
- WPA (2003)

Types of Rivest Cipher 4

- Spritz
- RC4A
- VMPC
- RC4A+

The stream ciphers used by RC4 ensure easy implementation and are, therefore, widely used. Unlike AES, RC4 lacks strict security small data streams cannot be encoded by implementing RC4.

**Main Differences Between AES and RC4**

- AES or Advanced Encryption Standard is a block cipher whereas Rivest Cipher 4 is a stream cipher.
- As far as security is concerned, AES is more secure than RC4.
- AES is developed after RC4, the former was initiated in 1997, and the latter was developed in 1987.
- AES uses 128, 192, and 256 bits, whereas RC4 uses 64 bits and 128 bits key size.
- AES has a complex algorithm, whereas the encryption in RC4 is relatively simple.

**References**

- https://ieeexplore.ieee.org/abstract/document/1258477/
- https://asat.journals.ekb.eg/article_23497.html

Sandeep Bhandari holds a Bachelor of Engineering in Computers from Thapar University (2006). He has 20 years of experience in the technology field. He has a keen interest in various technical fields, including database systems, computer networks, and programming. You can read more about him on his bio page.