source: azure_iot_hub/trunk/musl-1.1.18/src/crypt/encrypt.c@ 389

#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>

struct expanded_key {
        uint32_t l[16], r[16];
};

void __des_setkey(const unsigned char *key, struct expanded_key *ekey);
void __do_des(uint32_t l_in, uint32_t r_in,
    uint32_t *l_out, uint32_t *r_out,
    uint32_t count, uint32_t saltbits, const struct expanded_key *ekey);


static struct expanded_key __encrypt_key;

void setkey(const char *key)
{
        unsigned char bkey[8];
        int i, j;

        for (i = 0; i < 8; i++) {
                bkey[i] = 0;
                for (j = 7; j >= 0; j--, key++)
                        bkey[i] |= (uint32_t)(*key & 1) << j;
        }

        __des_setkey(bkey, &__encrypt_key);
}

void encrypt(char *block, int edflag)
{
        struct expanded_key decrypt_key, *key;
        uint32_t b[2];
        int i, j;
        char *p;

        p = block;
        for (i = 0; i < 2; i++) {
                b[i] = 0;
                for (j = 31; j >= 0; j--, p++)
                        b[i] |= (uint32_t)(*p & 1) << j;
        }

        key = &__encrypt_key;
        if (edflag) {
                key = &decrypt_key;
                for (i = 0; i < 16; i++) {
                        decrypt_key.l[i] = __encrypt_key.l[15-i];
                        decrypt_key.r[i] = __encrypt_key.r[15-i];
                }
        }

        __do_des(b[0], b[1], b, b + 1, 1, 0, key);

        p = block;
        for (i = 0; i < 2; i++)
                for (j = 31; j >= 0; j--)
                        *p++ = b[i]>>j & 1;
}