SBG6580 3DES key conversion

convert_key.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static int convert_key(unsigned char *src, unsigned char *dst) {
    unsigned char v0, v1, a2, *v1x, a0x;

    // convert 7-bit groups to 8-bits
    v0 = src[0];
    v0 &= 0xFE;
    dst[0] = v0;

    v1 = src[1];
    v1 >>= 1;
    v1 &= 0x7E;
    v0 = src[0];
    v0 &= 1;
    v0 <<= 7;
    v1 += v0;
    dst[1] = v1;

    v1 = src[2];
    v1 >>= 2;
    v1 &= 0x3E;
    v0 = src[1];
    v0 &= 3;
    v0 <<= 6;
    v1 += v0;
    dst[2] = v1;

    v1 = src[3];
    v1 >>= 3;
    v1 &= 0x1E;
    v0 = src[2];
    v0 &= 7;
    v0 <<= 5;
    v1 += v0;
    dst[3] = v1;

    v1 = src[4];
    v1 >>= 4;
    v1 &= 0xE;
    v0 = src[3];
    v0 &= 0xF;
    v0 <<= 4;
    v1 += v0;
    dst[4] = v1;

    v1 = src[5];
    v1 >>= 5;
    v1 &= 6;
    v0 = src[4];
    v0 &= 0x1F;
    v0 <<= 3;
    v1 += v0;
    dst[5] = v1;

    v1 = src[6];
    v1 >>= 6;
    v1 &= 2;
    v0 = src[5];
    v0 &= 0x3F;
    v0 <<= 2;
    v1 += v0;
    dst[6] = v1;

    v0 = src[6];
    v0 <<= 1;
    dst[7] = v0;

    // compute the parity bit
    a2 = 0;
    v1x = &dst[a2];
    do {
        v0 = v1x[0];
        v0 ^= 1;
        v1x[0] = v0;
        a0x = 1;
        v0 = v1x[0];

        do {
            v0 = (char)v0 >> a0x;
            v0 &= 1;
            a0x += 1;
            if (v0 != 0) {
                v0 = v1x[0];
                v0 ^= 1;
                v1x[0] = v0;
            }

            v0 = v1x[0];
        } while (a0x < 8);

        a2 += 1;
        v1x = &dst[a2];
    } while (a2 < 8);

    return 0;
}

static int derive_key(unsigned char *src, unsigned char *dst) {
    for (int j = 0; j < 7; j++) {
        for (int i = 0; i < 3; i++) {
            dst[7*i + j] = src[3*j + i] - j;
        }
    }
    return 0;
}

int main(int argc, const char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "%s\n", "invalid args\n");
        return 1;
    }
    if (strnlen(argv[1], 64) != 42) {
        fprintf(stderr, "%s\n", "key must be 42 hex characters\n");
    }

    fprintf(stderr, "in : ");
    unsigned char in[21];
    for (int i = 0; i < 21; i++) {
        char sym[3];
        int cur;
        int conv;
        sym[0] = argv[1][2*i];
        sym[1] = argv[1][2*i+1];
        sym[2] = '\0';
        cur = strtoul(sym, NULL, 16);
        fprintf(stderr, "%02X", cur);

        in[i] = cur;
    }
    fprintf(stderr, "\n");

    unsigned char drv[21];
    derive_key(in, drv);

    printf("out: ");
    for (int i = 0; i < 3; i++) {
        unsigned char dst[8];
        convert_key(&drv[7*i], dst);
        for (int j = 0; j < 8; j++) {
            printf("%02X", dst[j]);
        }
    }
    printf("\n");
    return 0;
}