Cryptography series: SAFER

Introduction

Block cipher is an excellent encryption structure. Many commonly used encryption algorithms use block algorithms, such as DES. SAFER also represents a block cipher algorithm. Let's take a look.

Introduction to SAFER

The full name of SAFER is Secure And Fast Encryption Routine. In cryptography, SAFER is mainly a set of block ciphers designed by James Massey (one of IDEA's designers) on behalf of Cylink.

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

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

The following SAFER+ and SAFER++ were submitted to NESSIE as candidate algorithms for the AES algorithm. All algorithms in the SAFER series have no patent restrictions and can be used for free.

SAFER K and SAFER SK

The first SAFER cipher was SAFER K-64 released by Massey in 1993, with a 64-bit block size. "K-64" represents a 64-bit key size.

Because the 64-bit block is too small to be suitable for encrypting large data, Massey released a 128-bit variant called SAFER K-128 the following year.

However, Lars Knudsen and Sean Murphy found that this version had some problems, so they redesigned the key scheduling according to Knudsen's suggestion. These variant algorithms are named SAFER SK-64 and SAFER SK-128 respectively.

Among them, "SK" stands for "Strengthened Key schedule", which is the enhanced time schedule.

In addition, there is a variant algorithm SAFER SK-40 with a block size of 40 bits.

We use a diagram to look at the basic flow of the SAFER K algorithm:

Starting from the top, is the input stage of the plaintext, and each plaintext is divided into 8 blocks.

Then there is the key mixing stage. In this stage, the plaintext is added modulo 256 or XOR operation with the subkey respectively.

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

The two S boxes are derived from the functions ^x and log ₄₅ Those who want to know the S-box can refer to the article "Cryptography Series: Blowfish Symmetric Key Grouping Algorithm".

Then comes the second key mixing phase.

After the second key mixing phase, pseudo-Hadamard transform (PHT) will be used for diffusion.

These four stages constitute 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 and Massey.

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

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

This article has been included in http://www.flydean.com/safer/

The most popular interpretation, the most profound dry goods, the most concise tutorial, and many tips you don't know are waiting for you to discover!

Welcome to pay attention to my official account: "Program those things", know technology, know you better!