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Cryptography – SEED Encryption Algorithm

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SEED encryption is a symmetric key encryption technique created by the Korean Information Security Agency. It is a block cipher encryption technique which works with 16-byte data blocks and a 128-bit key length.

The SEED encryption algorithm encrypts plain text data into cipher text by combining substitution and permutation techniques. To generate the final cipher text, the process uses a Feistel network structure that goes through several rounds of encryption.

Encryption of SEED

SEED encryption uses a key schedule to create round keys, which are used in each round of encryption.
The key schedule is created by performing a series of bitwise operations on the original key, like XOR, AND, and left and right shifts.
The encryption procedure requires dividing the plain text into 16-byte blocks and executing the encryption algorithm to each block separately.
The algorithm encrypts the data using a combination of substitution and permutation algorithms, and then applies numerous rounds of encryption to each block to produce the final cipher text.

Decryption of SEED

The decryption procedure reverses the encryption process.
The cipher text is divided into 16-byte blocks, and the decryption technique is executed to each block individually, using the identical round keys created during the encryption procedure.

Structure of SEED

SEED”s input/output block size and key length are both 128 bits. SEED features a 16-round Feistel structure. A 128-bit input is separated into two 64-bit blocks (L, R). The right 64-bit block is used to input the round function F, which generates a 64-bit subkey Ki based on the key schedule.

A pseudo code for SEED”s structure is as follows −

for (i = 1; i <= 16; i++) {
   L = R;
   R = L ^ F(Ki, R);
}

Round Function F

SEED makes use of two 8×8 S-boxes, permutations, rotations, and fundamental modular operations like exclusive OR (XOR) and adds to ensure huge security, speed, and simplicity in implementation.

The round function F divides a 64-bit input block into two 32-bit blocks (R0, R1) and uses four phases −

A mixing phase for two 32-bit subkey blocks (Ki0, Ki1).
Function G has three layers and allows for the mixing of two 32-bit blocks.

Function F produces the following outputs (R0” and R1”) −

R0'' = G[G[G[(R0 ^ Ki0) ^ (R1 ^ Ki1)] + (R0 ^ Ki0)] + G[(R0 ^ Ki0) ^ (R1 ^ Ki1)] + G[G[(R0 ^ Ki0) ^ (R1 ^ Ki1)] + (R0 ^ Ki0)]

R1'' = G[G[G[(R0 ^ Ki0) ^ (R1 ^ Ki1)] + (R0 ^ Ki0)]. + G[(R0 ^ Ki0) ^ (R1 ^ Ki1)] + G[G[(R0 ^ Ki0) ^ (R1 ^ Ki1)]

Function G

The function G consists of two layers: two 8×8 S-boxes and block permutation with sixteen 8-bit sub-blocks. The function G with four 8-bit inputs (X0, X1, X2, and X3) gives the following outputs −

Z0 equals {S1(X0) & m0} ^ {S2(X1) & m1} ^ {S1(X2) & m2} ^ {S2(X3) & m3}
Z1 equals {S1(X0) & m1} ^ {S2(X1) & m2} ^ {S1(X2) & m3} ^ {S2(X3) & m0}
Z2 equals {S1(X0) & m2} ^ {S2(X1) & m3} ^ {S1(X2) & m0} ^ {S2(X3) & m1}
Z3 equals {S1(X0) & m3} ^ {S2(X1) & m0} ^ {S1(X2) & m1} ^ {S2(X3) & m2}

where m0 = 0xfc; m1 = 0xf3; m2 = 0xcf; and m3 = 0x3f.

To improve G function efficiency, four ”SS-box” are defined as follows −

SS0(X) = {S1(X)& m3} || {S1(X) & m2} || {S1(X) & m1} || {S1(X) & m0}
SS1(X) = {S2(X) & m0} || {S2(X) & m3} || {S2(X) & m2} || {S2(X) & m1}
SS2(X) = {S1(X) & m1} || {S1(X) & m0} || {S1(X) & m3} || {S1(X) & m2}
SS3(X) = {S2(X) & m2} || {S2(X) & m1} || {S2(X) & m0} || {S2(X) & m3}

Applications of SEED

SEED encryption is used to secure network communication, which includes VPNs, SSL/TLS, and IPsec.
SEED encryption secures data saved on discs, USB drives, and other storage media.
This encryption technique is used to protect data on mobile devices like smartphones and tablets.
Government agencies and military organisations utilise SEED encryption to secure confidential material.

Advantages

Below are some advantages and benifits of using SEED encryption technique −

SEED encryption has a 128-bit key length, making it highly resistant to brute force attacks.
SEED encryption is a rapid method that can encrypt and decrypt data easily, making it ideal for real-time applications.
SEED encryption is widely used and supported by various security products and services.
SEED encryption can be utilised in a wide range of applications, like network security, data storage, and mobile devices.
SEED encryption has undergone substantial research and is resistant to several known cryptanalysis attacks.

Disadvantages

Besides the advantages of SEED algorithm it also has some disadvantages of using it.

SEED encryption needs good key management because the encryption”s security is dependent on the key”s strength and confidentiality.
SEED encryption has a key length of 128 bits, which can be insufficient for some applications that demand stronger encryption.
SEED encryption is subject to side-channel attacks such as timing and power analysis.

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