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# Difference between AES and Twofish

AES (Advanced Encryption Standard) and Twofish are both symmetric key block cyphers, which means they encrypt and decrypt data using the same secret key. While the two algorithms have certain similarities, they also have some significant variations.

In terms of performance, AES exceeds Twofish in hardware implementations, although Twofish might exceed AES in software implementations. This is due to the fact that Twofish has a more complex key schedule and a greater number of rounds than AES.

Read this article to find out more about AES and Twofish and how they are different from each other.

## What is AES?

AES (Advanced Encryption Standard) is a commonly used symmetric key block cypher technique for encrypting and decrypting data. It was created by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, and was chosen as the standard for encrypting sensitive government information by the United States National Institute of Standards and Technology (NIST).

The first phase in the method is the key schedule, in which the input key is expanded into a number of round keys, one for each round of encryption. The number of rounds varies with the key size, with a 128-bit key requiring 10 rounds, a 192-bit key requiring 12 rounds, and a 256-bit key requiring 14 rounds.

SubBytes, ShiftRows, MixColumns, and AddRoundKey are the four operations that form each round. Each byte of the input block is replaced with a corresponding byte from the S-box substitution table in the SubBytes phase. This phase gives the algorithm non-linearity and helps in the prevention of basic attacks.

The rows of the input block are shifted by a specified number of bytes according to the row number in the ShiftRows step. This phase ensures that the algorithm's output is dependent on all of the input bytes and provides diffusion.

Each column of the input block is modified using matrix multiplication in the MixColumns step. This stage provides diffusion and helps in the prevention of linear equation-based attacks.

The round key for the current round is XORed with the input block in the AddRoundKey step. This step ensures that the input block is key-dependent and causes confusion.

After the final round, the output block is obtained, which is the encrypted version of the input block. To decrypt the data, the encryption process is reversed by applying the inverse of each step in reverse order while using the same key.

## What is Twofish?

Bruce Schneier, John Kelsey, Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson created the Twofish symmetric key block cypher algorithm. It is the Blowfish cypher's successor and one of the five finalists in the AES competition.

The key schedule is the algorithm's first stage, in which the input key is split into a number of subkeys, one for each round of encryption. The number of rounds depends on the block and key sizes, with a 128-bit block and 128-bit key receiving 16 rounds, a 192-bit block and key receiving 16 or 20 rounds, and a 256-bit block and key receiving 16, 20, or 24 rounds.

Substitution, permutation, mixing, and key addition are the four steps in each round. Each byte of the input block is replaced with a corresponding byte from four 8x8 S-boxes during the substitution stage. S-boxes provide non-linearity and are selected to be resistant to recognised attacks.

The order of the bytes in the input block is modified according to a specified permutation table in the permutation step. This phase provides diffusion and helps in the prevention of simple attacks.

The bytes in the input block are combined in the mixing stage using a mixing function that uses modular multiplication in a finite field. This stage provides diffusion and helps in the prevention of linear equation-based attacks.

The round subkey for the current round is XORed with the input block in the Key Addition stage. This step ensures that the input block is key-dependent and causes confusion.

After the final round, the output block is obtained, which is the encrypted version of the input block. To decrypt the data, the encryption process is reversed by applying the inverse of each step in reverse order while using the same key.

## Difference between AES and Twofish

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

Characteristics |
AES |
Twofish |
---|---|---|

Block Size |
128 bits |
128, 192, or 256 bits |

Key Size |
128, 192, or 256 bits |
Up to 256 bits |

Number of Rounds |
10, 12, or 14 rounds |
16, 20, or 24 rounds |

Key Schedule |
Simple |
more complex and slower |

Speed |
Faster than Twofish |
Slower than AES |

Strength |
Strong against known attacks |
Strong against known attacks |

Implementation |
More widely implemented and standardized |
Less widely implemented and not as standardized. |

Flexibility |
Fixed block size and the number of rounds |
Variable block size and the number of rounds |

## Conclusion

In conclusion, Twofish has a variable block size of 128, 192, or 256 bits and supports key sizes of up to 256 bits, whereas AES has a fixed block size of 128 bits and supports key sizes of 128, 192, or 256 bits.

In hardware implementations, AES is often faster than Twofish, whereas Twofish may be faster in software implementations. Government agencies and enterprises have widely implemented AES, whereas Twofish has not been as widely adopted.

Overall, the decision between AES and Twofish depends on the application's and security requirements. Both cyphers are very secure and can provide strong encryption, although differences in their properties may make one more suitable for particular applications than the other.