Difference Between AES and RC4 (2024)

The cryptographic algorithms AES (Advanced Encryption Standard) and RC4 (Rivest Cipher 4) are both used for encryption; however, they differ significantly in terms of security, usage, and design. Read this article to find out more about AES and RC4 and how they are different from each other.

What is AES?

AES (Advanced Encryption Standard) is a popular symmetric block cipher encryption algorithm for protecting sensitive data. It was chosen in 2001 by the United States National Institute of Standards and Technology (NIST) to replace the outdated Data Encryption Standard (DES) as the new encryption standard.

Key Features of AES

• Symmetric Encryption − AES is a symmetric encryption technique, which means it uses the same key for both data encryption and decryption. To securely communicate, both the sender and the recipient must have the same secret key.

• Block Cipher − During encryption and decryption, AES uses fixed-size blocks of data. 128 bits (16 bytes) is the block size. Each 128-bit block is subdivided into a 4x4 byte matrix known as the State.

• Key Sizes − AES has three key sizes − 128, 192, and 256 bits. The number of rounds used in the method is determined by the key size. The more rounds of encryption, the safer the encryption, but the slower the process.

• Security − When used with proper key lengths, AES has undergone rigorous research and is regarded very secure. Because of its resistance to multiple threats, it is useful for protecting sensitive data in a variety of applications, including secure communications, financial transactions, and data storage.

AES Encryption Process

• Key Expansion − For each encryption round, the initial encryption key is enlarged to generate round keys.

• Initial Round − Using the AddRoundKey method, the first round key is combined with the plaintext.

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• Main Rounds − Each round consists of SubBytes, ShiftRows, MixColumns, and AddRoundKey operations, and the number of rounds is determined by the key size.

• Final Round − To provide a clearer decryption process, the final round bypasses the MixColumns operation.

AES Decryption Process

AES decryption is the opposite of encryption, using the same key schedule but utilizing the inverse procedures of SubBytes, ShiftRows, and MixColumns. For encryption and decryption, the AddRoundKey operation is the same.

What is RC4?

Ron Rivest invented the RC4 (Rivest Cipher 4) symmetric stream cipher encryption technique in 1987. Because of its simplicity and efficiency, it is frequently used for secure communications and data encryption. However, severe security flaws were uncovered over time, leading to its deprecation and the recommendation that it be replaced by more secure algorithms such as AES.

Key Features of RC4

• Symmetric Stream Cipher − RC4 is a symmetric encryption technique, which means it uses the same secret key for encryption and decoding. It works with individual bytes of data (a stream) rather than fixed-size blocks like block ciphers like AES.

• Key Sizes − RC4 allows for various key sizes, ranging from 40 to 2048 bits. The complexity of the encryption process is determined by the length of the key. However, due to specific limitations, longer keys do not always give greater security with RC4.

• Pseudo-Random Number Generator (PRNG) − To generate the ciphertext, RC4 uses a PRNG to generate a keystream, which is then merged with the plaintext using bitwise XOR. The RC4 algorithm relies heavily on keystream creation.

• RC4 Encryption Process − After generating the keystream, it is combined with the plaintext using bitwise XOR to form the ciphertext.

• RC4 Security Issues − Despite its widespread use in the past, RC4 has been discovered to have severe security flaws. The "RC4 bias," which results in a non-uniform distribution of the generated keystream, is the most significant fault. This bias results in statistical correlations, which attackers can use to retrieve portions of the plaintext if they have access to enough ciphertext.

Difference between AES and RC4

The following table highlights the major differences between AES and RC4 −

Conclusion

In conclusion, AES is a powerful and widely regarded encryption standard that can be used for a variety of applications, whereas RC4 is an obsolete algorithm with documented limitations that is no longer recommended for secure communication.