International Date Encryption Algorithm (IDEA)

Module - 2 YM 3 w International Date Encryption Algorithm (IDE - it is a symmetric encryption algorithm - -It was known to be as IPES (improved proposed encyclin standard) 64 bit PT is used and 64 bit CT - key : 128bit g - published in 1991 - Has similiarities with DES - it is using rounds 8 rounds - Mong le: function is used here. which is the modified version of fk in DES. Mangular function is irreversible - Eneryption and decryption Keys are different here PT divided into 4 blocks. 64 = 16 bits Each 8 4 rounds are splitted into 2 - as 099 runds and even rounds : and an extra round is provided it is called output transfirmation 8 rounds 8 oddrounds seven rounds 16 rounds + 101 trans formation

17 round s + - Uses bit addition wise X-OR modulo 216 (it 16+1 + uses x - - uses multiplication modulo 2 * Page: 68. (photostat) Fig. 2.2. SD It is an overview of IDEA - The 64 bit datablock is divided into 4 16bit subblocks : 11,22,23 and 24 - Thise 4 subblocks become the /P to the 1st round of the algorithm - There are 8 rounds in total. - In each round, the 4 subblocks are ExoRed C added and multiplied with one another and with 6 16 bit 1 sub B/W keys rounds most the 2nd and 3rd subblocks are swapped T with the 4 subkey's in an olp finally the 4 subblocks are combined transformation - In each round the sequence of events is as follows : 1. Multiply X1 and the 1st subkey. 2. Add x2 and the 2nd subkey. 3. Add %3 and the 3°9 subkey 4. Multiply X4 and the 4th subkey. 5. XOR the results of steps 1 and 3. 6. XOR the results of steps 2 and 4 7. Multiply the results of step 5 with 5th subkey

8. Add the results of step 687 9. Multiply the results of step 8 with the 6th subkey. 10. Add the results of steps 7 &9. 11. XOR the results of steps ando 12. XOR the results of steps apda 13. XOR the results of steps 2 and 10 14. XOR the results of steps 4 andle - 4 subblocks that are the results of The output of the round is the steps 11 / 12, 13 & 14 Swap the 2 inner blocks ( except for the last round) and that's the input to the next round After the 8th round, There is a - final o/p trans formation 1. Multiply x1 and the 1st subkey 2. Add x2 and the and subkey 3. Add x3 and the 3rd subkey. 4. Multiply x4 and The 4th subkey - Finally the 4 subblocks are reattached to produce the cipheo text

AES 128 bit PT is used Published in 2001. It is a symmetric block cipher replaces DES 10 rounds - 128bit 12 rounds - 192 bits 14 rounds - 256 bits Rounds consists of following operations: 1) Add Round key 2) Subsh tute bytes 3) shift rows 4) mix coloumns