Introduction to the

IDEA stands for International Data Encryption Algorithm, also known as International Encryption Algorithm. Note that this is not the development tool IDEA we commonly use.

Today I would like to introduce my IDEA in detail.

Introduction of the IDEA

IDEA is called International Encryption Algorithm in Chinese, and was originally called Improved Proposed Encryption Standard (IPES). It is a symmetric key encryption algorithm, originally proposed by James Massey and Xuejia Lai in 1991.

The goal is to replace the DES algorithm. IDEA is a revision of earlier PES. IDEA is an optional algorithm of the OpenPGP standard.

IDEA’s patent expired in 2012 and is now free to use.

The IDEA of principle

The length of the IDEA encryption block is 64bits, and the length of the key is 128bits. It is a combination of eight-round transform and half-round output transform. The process of encryption and decryption is similar. Let’s look at the basic flow chart of IDEA:

In the figure above, the blue circle is the XOR XOR operation and the green box is the addition module 216. The red dot is multiplied by mod 216 + 1, which will be converted to 216 if the input is both 0 (0x0000) and 0 if the input is 216 (0x0000).

After eight rounds, the output of the next half round is converted as follows (the swap of the middle two values cancels out the swap at the end of the last round, so there is no net swap) :

IDEA Sub-key generation

IDEA uses the LAI-Massey structure. Each round uses six 16-place keys, and the last half round uses four subkeys for a total of 8.5 rounds of 52 subkeys.

The first eight subkeys are extracted directly from the key, because the length of the key is 128bits, which can be divided into eight 16-bit self-keys. K1 of the first round is 16 bits of the key.

More sets of eight subkeys are created by moving the master key 25 bits to the left between each set of eight.

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

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