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What is IDEA in Information Security?
IDEA stands for International Data Encryption Algorithm. IDEA is a block cipher invented by James Massey and Xuejia Lai and was first defined in 1991. It uses 128 bit key length which works on 64 bit blocks.
It includes a series of eight identical transformations depend upon bitwise exclusiveor, addition and multiplication modules. It is based upon symmetric cipher and has very weak key design approach therefore security level of the algorithm is very underprivileged as compared to the DES. IDEA not becomes so much famous because of its complex structure.
It is an IDEA, unlike the other block cipher algorithms is considered by the Swiss firm of Ascom. However, be unique in allow with permission with free non-commercial use of their algorithm which the result that IDEA is popular as the block cipher algorithm used within the famous encryption for the message character.
There are eight rounds in IDEA. Each round includes a sequence of operations on the four data blocks using six keys. For the first round, it can have key K1 to K6, for second round it can have keys K7 to K12 and finally the last round. The final step includes an output transformation, which needs four subkeys (K49 to K52).
The final output is the output developed by the output transformation step. The blocks C1 to C4 are linked to form the final output. Each round includes 14 steps are as follows −
Details of one round in IDEA
| Step1 : Multiply * P1 and K1 |
| Step2 : Add * P2and K2 |
| Step3 : Add * P3and K3 |
| Step4 : Multiply * P4 and K4 |
| Step5 : XOR the results of step1 and step3 |
| Step6 : XOR the results of step2 and step4 |
| Step7 : Multiply * the results of step5 with K5 |
| Step8 : Add * the results of step6 and step7 |
| Step9 : Multiply * the results of step8 with K6 |
| Step10 : Add * the results of step7 and step9 |
| Step11 : XOR the results of step1 and step9 |
| Step12 : XOR the results of step3 and step9 |
| Step13 : XOR the results of step2 and step10 |
| Step14 : XOR the results of step4 and step10 |
The Add * and Multiply * in the following step of each round are not elementary addition and multiplication but they are addition module 216 i.e., 65536 and Multiplication Module 216 + 1 i. e. , 65537.
Output Transformation − It is a one-time operation. It takes place endmost of the 8th round. Therefore 64-bit value is divided into four sub-blocks (say R1 to R4) and four subkeys are used here.
Decryption − The Decryption implements like encryption, but the order of the round keys is produced, and the subkeys for the odd rounds are inversed into this. Thus, the values of subkeys K1-K4 are restored by the inverse of K49-K52 for the respective set operation in the cryptography, K5, and K6 of each group should be restored by K47 and K48 for decryption in this operation in the cryptography.
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