pwdauth.c

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/*      pwdauth 2.0 - check a shadow password           Author: Kees J. Bot
 *                                                              7 Feb 1994
 *
 * This program gets as input the key and salt arguments of the crypt(3)
 * function as two null terminated strings.  The crypt result is output as
 * one null terminated string.  Input and output must be <= 1024 characters.
 * The exit code will be 1 on any error.
 *
 * If the key has the form '##name' then the key will be encrypted and the
 * result checked to be equal to the encrypted password in the shadow password
 * file.  If equal than '##name' will be returned, otherwise exit code 2.
 *
 * Otherwise the key will be encrypted normally and the result returned.
 *
 * As a special case, anything matches a null encrypted password to allow
 * a no-password login.
 */
#define nil 0
#define crypt   CRYPT   /* The true crypt is included here. */
#include <sys/types.h>
#include <pwd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#define LEN     1024
char SHADOW[] = "/etc/shadow";

int main(int argc, char **argv)
{
        char key[LEN];
        char *salt;
        struct passwd *pw;
        int n;

        /* Read input data.  Check if there are exactly two null terminated
         * strings.
         */
        n= read(0, key, LEN);
        if (n < 0) return 1;
        salt = key + n;
        n = 0;
        while (salt > key) if (*--salt == 0) n++;
        if (n != 2) return 1;
        salt = key + strlen(key) + 1;

        if (salt[0] == '#' && salt[1] == '#') {
                /* Get the encrypted password from the shadow password file,
                 * encrypt key and compare.
                 */
                setpwfile(SHADOW);

                if ((pw= getpwnam(salt + 2)) == nil) return 2;

                /* A null encrypted password matches a null key, otherwise
                 * do the normal crypt(3) authentication check.
                 */
                if (*pw->pw_passwd == 0 && *key == 0) {
                        /* fine */
                } else
                if (strcmp(crypt(key, pw->pw_passwd), pw->pw_passwd) != 0) {
                        return 2;
                }
        } else {
                /* Normal encryption. */
                if (*salt == 0 && *key == 0) {
                        /* fine */
                } else {
                        salt= crypt(key, salt);
                }
        }

        /* Return the (possibly new) salt to the caller. */
        if (write(1, salt, strlen(salt) + 1) < 0) return 1;
        return 0;
}

/* The one and only crypt(3) function. */

/*      From Andy Tanenbaum's book "Computer Networks",
        rewritten in C
*/

struct block {
        unsigned char b_data[64];
};

struct ordering {
        unsigned char o_data[64];
};

static struct block key;

static struct ordering InitialTr = {
        58,50,42,34,26,18,10, 2,60,52,44,36,28,20,12, 4,
        62,54,46,38,30,22,14, 6,64,56,48,40,32,24,16, 8,
        57,49,41,33,25,17, 9, 1,59,51,43,35,27,19,11, 3,
        61,53,45,37,29,21,13, 5,63,55,47,39,31,23,15, 7,
};

static struct ordering FinalTr = {
        40, 8,48,16,56,24,64,32,39, 7,47,15,55,23,63,31,
        38, 6,46,14,54,22,62,30,37, 5,45,13,53,21,61,29,
        36, 4,44,12,52,20,60,28,35, 3,43,11,51,19,59,27,
        34, 2,42,10,50,18,58,26,33, 1,41, 9,49,17,57,25,
};

static struct ordering swap = {
        33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,
        49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,
         1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15,16,
        17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,
};

static struct ordering KeyTr1 = {
        57,49,41,33,25,17, 9, 1,58,50,42,34,26,18,
        10, 2,59,51,43,35,27,19,11, 3,60,52,44,36,
        63,55,47,39,31,23,15, 7,62,54,46,38,30,22,
        14, 6,61,53,45,37,29,21,13, 5,28,20,12, 4,
};

static struct ordering KeyTr2 = {
        14,17,11,24, 1, 5, 3,28,15, 6,21,10,
        23,19,12, 4,26, 8,16, 7,27,20,13, 2,
        41,52,31,37,47,55,30,40,51,45,33,48,
        44,49,39,56,34,53,46,42,50,36,29,32,
};

static struct ordering etr = {
        32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9,
         8, 9,10,11,12,13,12,13,14,15,16,17,
        16,17,18,19,20,21,20,21,22,23,24,25,
        24,25,26,27,28,29,28,29,30,31,32, 1,
};

static struct ordering ptr = {
        16, 7,20,21,29,12,28,17, 1,15,23,26, 5,18,31,10,
         2, 8,24,14,32,27, 3, 9,19,13,30, 6,22,11, 4,25,
};

static unsigned char s_boxes[8][64] = {
{       14, 4,13, 1, 2,15,11, 8, 3,10, 6,12, 5, 9, 0, 7,
         0,15, 7, 4,14, 2,13, 1,10, 6,12,11, 9, 5, 3, 8,
         4, 1,14, 8,13, 6, 2,11,15,12, 9, 7, 3,10, 5, 0,
        15,12, 8, 2, 4, 9, 1, 7, 5,11, 3,14,10, 0, 6,13,
},

{       15, 1, 8,14, 6,11, 3, 4, 9, 7, 2,13,12, 0, 5,10,
         3,13, 4, 7,15, 2, 8,14,12, 0, 1,10, 6, 9,11, 5,
         0,14, 7,11,10, 4,13, 1, 5, 8,12, 6, 9, 3, 2,15,
        13, 8,10, 1, 3,15, 4, 2,11, 6, 7,12, 0, 5,14, 9,
},

{       10, 0, 9,14, 6, 3,15, 5, 1,13,12, 7,11, 4, 2, 8,
        13, 7, 0, 9, 3, 4, 6,10, 2, 8, 5,14,12,11,15, 1,
        13, 6, 4, 9, 8,15, 3, 0,11, 1, 2,12, 5,10,14, 7,
         1,10,13, 0, 6, 9, 8, 7, 4,15,14, 3,11, 5, 2,12,
},

{        7,13,14, 3, 0, 6, 9,10, 1, 2, 8, 5,11,12, 4,15,
        13, 8,11, 5, 6,15, 0, 3, 4, 7, 2,12, 1,10,14, 9,
        10, 6, 9, 0,12,11, 7,13,15, 1, 3,14, 5, 2, 8, 4,
         3,15, 0, 6,10, 1,13, 8, 9, 4, 5,11,12, 7, 2,14,
},

{        2,12, 4, 1, 7,10,11, 6, 8, 5, 3,15,13, 0,14, 9,
        14,11, 2,12, 4, 7,13, 1, 5, 0,15,10, 3, 9, 8, 6,
         4, 2, 1,11,10,13, 7, 8,15, 9,12, 5, 6, 3, 0,14,
        11, 8,12, 7, 1,14, 2,13, 6,15, 0, 9,10, 4, 5, 3,
},

{       12, 1,10,15, 9, 2, 6, 8, 0,13, 3, 4,14, 7, 5,11,
        10,15, 4, 2, 7,12, 9, 5, 6, 1,13,14, 0,11, 3, 8,
         9,14,15, 5, 2, 8,12, 3, 7, 0, 4,10, 1,13,11, 6,
         4, 3, 2,12, 9, 5,15,10,11,14, 1, 7, 6, 0, 8,13,
},

{        4,11, 2,14,15, 0, 8,13, 3,12, 9, 7, 5,10, 6, 1,
        13, 0,11, 7, 4, 9, 1,10,14, 3, 5,12, 2,15, 8, 6,
         1, 4,11,13,12, 3, 7,14,10,15, 6, 8, 0, 5, 9, 2,
         6,11,13, 8, 1, 4,10, 7, 9, 5, 0,15,14, 2, 3,12,
},

{       13, 2, 8, 4, 6,15,11, 1,10, 9, 3,14, 5, 0,12, 7,
         1,15,13, 8,10, 3, 7, 4,12, 5, 6,11, 0,14, 9, 2,
         7,11, 4, 1, 9,12,14, 2, 0, 6,10,13,15, 3, 5, 8,
         2, 1,14, 7, 4,10, 8,13,15,12, 9, 0, 3, 5, 6,11,
},
};

static int rots[] = {
        1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1,
};

static void transpose(struct block *data, struct ordering *t, int n)
{
        struct block x;

        x = *data;

        while (n-- > 0) {
                data->b_data[n] = x.b_data[t->o_data[n] - 1];
        }
}

static void rotate(struct block *key)
{
        unsigned char *p = key->b_data;
        unsigned char *ep = &(key->b_data[55]);
        int data0 = key->b_data[0], data28 = key->b_data[28];

        while (p++ < ep) *(p-1) = *p;
        key->b_data[27] = data0;
        key->b_data[55] = data28;
}

static struct ordering *EP = &etr;

static void f(int i, struct block *key, struct block *a, struct block *x)
{
        struct block e, ikey, y;
        int k;
        unsigned char *p, *q, *r;

        e = *a;
        transpose(&e, EP, 48);
        for (k = rots[i]; k; k--) rotate(key);
        ikey = *key;
        transpose(&ikey, &KeyTr2, 48);
        p = &(y.b_data[48]);
        q = &(e.b_data[48]);
        r = &(ikey.b_data[48]);
        while (p > y.b_data) {
                *--p = *--q ^ *--r;
        }
        q = x->b_data;
        for (k = 0; k < 8; k++) {
                int xb, r;

                r = *p++ << 5;
                r += *p++ << 3;
                r += *p++ << 2;
                r += *p++ << 1;
                r += *p++;
                r += *p++ << 4;

                xb = s_boxes[k][r];

                *q++ = (xb >> 3) & 1;
                *q++ = (xb>>2) & 1;
                *q++ = (xb>>1) & 1;
                *q++ = (xb & 1);
        }
        transpose(x, &ptr, 32);
}

static void setkey(char *k)
{

        key = *((struct block *) k);
        transpose(&key, &KeyTr1, 56);
}

static void encrypt(char *blck, int edflag)
{
        struct block *p = (struct block *) blck;
        int i;

        transpose(p, &InitialTr, 64);
        for (i = 15; i>= 0; i--) {
                int j = edflag ? i : 15 - i;
                int k;
                struct block b, x;

                b = *p;
                for (k = 31; k >= 0; k--) {
                        p->b_data[k] = b.b_data[k + 32];
                }
                f(j, &key, p, &x);
                for (k = 31; k >= 0; k--) {
                        p->b_data[k+32] = b.b_data[k] ^ x.b_data[k];
                }
        }
        transpose(p, &swap, 64);
        transpose(p, &FinalTr, 64);
}

char *crypt(const char *pw, const char *salt)
{
        char pwb[66];
        char *cp;
        static char result[16];
        char *p = pwb;
        struct ordering new_etr;
        int i;

        while (*pw && p < &pwb[64]) {
                int j = 7;

                while (j--) {
                        *p++ = (*pw >> j) & 01;
                }
                pw++;
                *p++ = 0;
        }
        while (p < &pwb[64]) *p++ = 0;

        setkey(p = pwb);

        while (p < &pwb[66]) *p++ = 0;

        new_etr = etr;
        EP = &new_etr;
        if (salt[0] == 0 || salt[1] == 0) salt = "**";
        for (i = 0; i < 2; i++) {
                char c = *salt++;
                int j;

                result[i] = c;
                if ( c > 'Z') c -= 6 + 7 + '.'; /* c was a lower case letter */
                else if ( c > '9') c -= 7 + '.';/* c was upper case letter */
                else c -= '.';                  /* c was digit, '.' or '/'. */
                                                /* now, 0 <= c <= 63 */
                for (j = 0; j < 6; j++) {
                        if ((c >> j) & 01) {
                                int t = 6*i + j;
                                int temp = new_etr.o_data[t];
                                new_etr.o_data[t] = new_etr.o_data[t+24];
                                new_etr.o_data[t+24] = temp;
                        }
                }
        }

        if (result[1] == 0) result[1] = result[0];

        for (i = 0; i < 25; i++) encrypt(pwb,0);
        EP = &etr;

        p = pwb;
        cp = result+2;
        while (p < &pwb[66]) {
                int c = 0;
                int j = 6;

                while (j--) {
                        c <<= 1;
                        c |= *p++;
                }
                c += '.';               /* becomes >= '.' */
                if (c > '9') c += 7;    /* not in [./0-9], becomes upper */
                if (c > 'Z') c += 6;    /* not in [A-Z], becomes lower */
                *cp++ = c;
        }
        *cp = 0;
        return result;
}

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