Introduction to the

Block cipher is a very good encryption structure, many commonly used encryption algorithms are using the block algorithm, such as DES. SAFER also stands for a block cipher algorithm. Take a look.

Introduction of SAFER

SAFER stands for Secure And Fast Encryption Routine. In cryptography, SAFER is mainly a group of block codes designed by James Massey (one of the designers of IDEA) on behalf of Cylink.

There are four types of SAFER: SAFER K, SAFER SK, SAFER+ and SAFER++.

SAFER K and SAFER SK are relatively early designs and share the same encryption function, but the rounds and key scheduling are different.

SAFER+ and SAFER++ were submitted to NESSIE as candidates for the AES algorithm. All of the algorithms in the SAFER series are patentless and free to use.

SAFER K and SAFER SK

The first SAFER password, the SAFER K-64, published by Massey in 1993, has a 64-bit block size. K-64 indicates the size of the 64-bit key.

Because 64-bit blocks were too small to encrypt large data, the following year Massey released a 128-bit variant called SAFER K-128.

However, Lars Knudsen and Sean Murphy found some problems with this version and redesigned the key scheduling as Knudsen suggested. These variants are named SAFER SK-64 and SAFER SK-128 respectively.

The “SK” stands for “Strengthened Key schedule”.

There is also a 40-bit block-size variant of the SAFER SK-40 algorithm.

We use a figure to see the basic process of the SAFER K algorithm:

Starting at the top, there is the input stage for plaintext, each of which is divided into eight pieces.

This is followed by the key mixing stage, in which the plaintext and the subkey are respectively added mode 256 or XOR.

Then there is the replacement phase, where the results generated in the previous phase are mapped to the new data through two opposite S-boxes.

The two S-boxes are derived from the functions 45x and log45, respectively. For those interested in s-boxes, see Blowfish Symmetric Key Grouping Algorithms in cryptography.

Then comes the second key mixing phase.

After the second key mixing phase, pseudo-hadamard Transform (PHT) is used for diffusion.

These four stages make up a round of encryption.

SAFER + and SAFER++

SAFER+ and SAFER++ are improvements to the original SAFER encryption algorithm. They were designed by Armenian cryptographers Gurgen Khachatrian (University of Armenia) and Melsik Kuregian with Massey.

SAFER + was proposed in 1998, but is submitted as a candidate for AES, with a 128-bit block size. The Bluetooth key is implemented based on the SAFER + custom algorithm (called E21 and E22),

SAFER ++ was submitted to the NESSIE project in 2000 in two versions, one 64-bit and one 128-bit.

This article is available at www.flydean.com/safer/

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