Input Array In Aes

Figure 1.0 From Neso Academy. It takes the input of 16 bytes 128 bits and outputs the ciphertext128 bits. Every 4 x 4 16 bytes are element state arrays that can store 16 bytes of information

The input bytes PlainText or CipherText are organized in groups of four bytes resulting 32-bit words. The words are placed in the matrix in the first column. After the first row is completed, the next column is initiated and the process continues until the input array is depleted. The input matrix is transferred to the State matrix Figure 2.

AES Key Expansion The AES key expansion algorithm takes as input a 4-word 16-byte key and produces a linear array of 44 words 176 bytes. This is sufficient to provide a 4-word round key for the initial AddRoundKey stage and each of the 10 rounds of the cipher. The following pseudocode describes the expansion

AES Example - Input 128 bit key and message Key in English Thats my Kung Fu 16 ASCII characters, 1 byte each Translation into Hex of current state matrix by corresponding entry in AES S-Box for instance byte 6E is substituted by entry of S-Box in row 6 and column E, i.e., by 9F this leads to new State Matrix 0 B B 63 EB 9F A0 C0 2F

In case of 16-byte key, AES key expansion algorithm takes as input a four-word 16- byte key and produces a linear array of 44 words 176 bytes. This is sufficient to provide a four-word round key for the initial AddRoundKey stage and each of the. 10 rounds of the cipher. Similar operation only done in case of 24 and 32 byte key lengths also.

AES operates on state, which stores the intermediate cipher result. It is a 2-D array having four rows and four columns For AES-128. The AES cipher is obtained by running a number of transformation rounds repeatedly that convert the plaintext original input into ciphertext encrypted output.

Each round of processing works on the input state array and produces an output state array. The output state array produced by the last round is rearranged into a 128-bit output block. Unlike DES, the decryption algorithm diers substantially from the encryption algorithm. Although, overall, very similar steps 5

AES is replacement of DES. AES works on block cipher technique. Size of plain text and cipher text must be same. An input key is also required input to the AES algorithm. Same size of plain text. In AES, the data length plain text size of 128 bits, and supporting three different key lengths, 128, 192 and 256 bits.

With AES we have blocks of 16 bytes 128 bits and with key sizes of 16, 24, 32 bytes. We go through a number of processes and where we operate on 16 bytes as an input and output. Figure 2. For example if the input byte is CF, then the output will be 8A. The inverse S-box does the reverse of the S-box process, so the DF maps back to CF

The AES encryption routine begins by copying the 16-byte input array into a 44 byte matrix named State see Figure 4. The AES encryption algorithm is named Cipher and operates on State Because AES uses so many arrays, there is a lot of index bounds checking that should be done. For example, the constructor presented does not even check