ISO 9797 algorithm 3

Last Friday I set out to implement ISO 9797 algorithm 3 using the OpenSSL library. I did not have the specification handy, so I decided to to the best I could with what I could find by way of examples on the net.


I came across a description of the algorithm in this 2005 thread (http://www.derkeiler.com/Newsgroups/sci.crypt/2005-02/0374.html). This was posted in a query by someone named Christian. He also posted his keys, data and the expected answer.

H0 = 0
stages 1 to n: Hj = Enc(K, Dj XOR H{j-1})
MAC = Enc(K, Dec(K', Hn))

Francois Grieu replied with, "This is very likely ISO/IEC 9797-1, using DES as the block cipher,
padding method 2, MAC algorithm 3." He provided an answer by sharing sample code in "some near-extinct dialect".

set m0 72C29C2371CC9BDB #message
set m1 65B779B8E8D37B29
set m2 ECC154AA56A8799F
set m3 AE2F498F76ED92F2

set pd 8000000000000000 #padding

set iv 0000000000000000 #initialisation vector

set k0 7962D9ECE03D1ACD #key
set k1 4C76089DCE131543

set xx {iv} # setup
for mj in {m0} {m1} {m2} {m3} {pd} # for each block including padding
 set xx `xor {xx} {mj}` # chain
 set xx `des -k {k0} -c {xx}` #encrypt
end
set xx `des -k {k1} -d {xx}` #decrypt
set xx `des -k {k0} -c {xx}` #encrypt
echo {xx} #show result

5F1448EEA8AD90A7 

I've implemented the same in c for the purpose of research.

#include openssl/des.h
#include memory
#include string.h

//message + padding
const unsigned char msg[40] = { 0x72, 0xC2, 0x9C, 0x23, 0x71, 0xCC, 0x9B, 0xDB,
                              0x65, 0xB7, 0x79, 0xB8, 0xE8, 0xD3, 0x7B, 0x29,
                              0xEC, 0xC1, 0x54, 0xAA, 0x56, 0xA8, 0x79, 0x9F,
                              0xAE, 0x2F, 0x49, 0x8F, 0x76, 0xED, 0x92, 0xF2,
                              0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };

//initialization vector
unsigned char iv[8] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };

unsigned char k0[8] = { 0x79, 0x62, 0xD9, 0xEC, 0xE0, 0x3D, 0x1A, 0xCD };
unsigned char k1[8] = { 0x4C, 0x76, 0x08, 0x9D, 0xCE, 0x13, 0x15, 0x43 };


void print_hex(const unsigned char *bs, int n) {

    for (int i = 0; i < n; i++)
        printf("%02x", bs[i]);
    printf("\n");
}

void des_ecb_crypt(unsigned char* input, unsigned char* output, int encrypt, unsigned char* key) {

    des_key_schedule sched;
    des_set_key((des_cblock *) key, sched);

    DES_ecb_encrypt((const_DES_cblock *)input,
                     (const_DES_cblock *)output,
                     &sched,
                     encrypt);
}

void xor_block(unsigned char* src, unsigned char* dest) {

    for (int x = 0; x < 8; x++) {
       src[x] =  src[x] ^ dest[x];
    }
}

int main(int argc, char* argv[]) {

    unsigned char output[8];
    unsigned char xx[8];
    unsigned char block[8];
    int offset = 0;

    memcpy(xx, iv, 8);

    // Chain and encrypt 5 8-bit blocks
    for (int x = 0; x < 5; x++) {

        memcpy(block, &msg[offset] , 8);
        offset+=8;

        //set xx `xor {xx} {mj}` # chain
        xor_block(xx, block);

        //set xx `des -k {k0} -c {xx}` #encrypt
        des_ecb_crypt(xx, output, DES_ENCRYPT, k0);
        memcpy(xx, output, 8);
    }


    des_ecb_crypt(xx, output, DES_DECRYPT, k1);
    memcpy(xx, output, 8);

    des_ecb_crypt(xx, output, DES_ENCRYPT, k0);
    memcpy(xx, output, 8);

    print_hex(xx, 8);
    return 1;
}