Convert an int array to an unsigned char array for AES encryption

Question

I got an array

int key[128] = {1,0,1,0,0,1, .........., 0,1,0}

I want to convert this array to

unsigned char key1[16] = {0x__,0x__,...,0x__}

for example if

from key[0] to key[7] is 10100011, then key1[0] = 0xa3

I need use this new array for AES encryption

If you need a fiexed bitwidth use fixed width types from `stdint.h`. Test also provide a defined representating of signed integers. — too honest for this site, Mar 19 '16 at 19:32
As I understand, you're asking how to *convert an array of integer 1's and 0's to a byte array*, and this has nothing to do with encryption. — Jonathon Reinhart, Mar 19 '16 at 19:55

xvan · Accepted Answer · 2016-03-19T20:02:03.287

0

This assumes that the lsb is key[0], and the msb is key[7]

int key[128] = {1,0,1,0,0,1, .........., 0,1,0}
unsigned char key1[16];

int (* better_key)[8] = (int (*)[8])key;

int i;
int j;

for (i=0;i<sizeof(key1); i++){
     key1[i]=0;
     for(j=0;j<8;j++){
       key1[i]|=better_key[i][j]<<j;
     }
}

If the msb is key[0], and the lsb is key[7], just replace

better_key[i][j]

with

better_key[i][7-j]

edited Mar 19 '16 at 20:02

answered Mar 19 '16 at 19:27

xvan

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score 0 · Answer 2 · answered Mar 19 '16 at 20:41

Go though each element of key[] adding (or'ing) in its bit-position value to the corresponding element of key1[].

#define N 128
#define B8 8

int key[N] = {1,0,1,0,0,1, .........., 0,1,0}
unsigned char key1[N/B8] = { 0 };

for (unsigned i = 0; i<N; i++) {
  key1[i/B8] |= key[i] << (B8 - 1 - (i%B8));
}

Convert an int array to an unsigned char array for AES encryption

2 Answers2