DES CBC Encryption Instance

Here is an example of a des CBC-based encryption form that I've tuned based on the STM32+POLARSSL encryption library. So that you can use it to do the right thing.

1. Use the DES-CBC encryption method and populate it with the Pkcs5padding method

2. Clear text for (string): <xml>123232</xml>

3. Generated ciphertext (hex data): 305f62576a76b23d6822b53fc537014058360a0d1696610b

4. Key is (string): rw4fef48

5. Initial Vector IV is: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

Pkcs5padding's explanation is as follows:

In pkcs5padding, it is clear that the size of the block is 8 bits, whereas in the pkcs7padding definition, the size of the block is indeterminate and can be between 1-255 (the length of the block is beyond 255), and the algorithm for populating the values is the same:
Value=k-(l mod k), k= block size, l= data length, if l=8, you need to populate additional 8 byte 8
The algorithm of the other side is:
Data to be padded
Pading = 8-(_raw_size% 8);
*_dst_size = _raw_size + pading;
for (i = _raw_size; i < *_dst_size; i++)
{
_raw_ptr[i] = pading;

}

The basic test procedure based on Polarssl is as follows:

unsigned char deskey1[9] = {"Rw4fef48"};
unsigned char pt[] = {' < ', ' x ', ' m ', ' l ', ' > ', ' 1 ', ' 2 ', ' 3 ', ' 2 ', ' 3 ', ' 2 ', ' < ', '/', ' X ', ' m ', ' l ', ' > '};
unsigned char cryt[64] = {0};
unsigned char iv[8] = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00};
Des_context CTX;
    
for (unsigned char i = 0; i < sizeof (Pt); i++)
{
    Cryt[i] = Pt[i];
}
unsigned char Index = sizeof (Pt);
unsigned char pading;
Pading = 8-(Index% 8);
for (unsigned char i = 0; i < pading; i++) 
{
    Cryt[index+i] = pading;
}
Des_setkey_enc (&ctx, (unsigned char *) DESKey1);
DES_CRYPT_CBC (&ctx, Des_encrypt, Index+pading, IV, Cryt, CRYT);
    
printf ("\ r \ n");
For (unsigned short i = 0; i < index+pading; i++)
{
    printf ("%02x", Cryt[i]);
}
printf ("\ r \ n");
    
memset (iv, 0, sizeof (iv));
Des_setkey_dec (&ctx, (unsigned char *) DESKey1);
DES_CRYPT_CBC (&ctx, Des_decrypt, Index+pading, IV, Cryt, CRYT);