2 * This function implements the "bigcrypt" algorithm specifically for
5 * This algorithm is algorithm 0 (default) shipped with the C2 secure
6 * implementation of Digital UNIX.
8 * Disclaimer: This work is not based on the source code to Digital
9 * UNIX, nor am I connected to Digital Equipment Corp, in any way
10 * other than as a customer. This code is based on published
11 * interfaces and reasonable guesswork.
13 * Description: The cleartext is divided into blocks of SEGMENT_SIZE=8
14 * characters or less. Each block is encrypted using the standard UNIX
15 * libc crypt function. The result of the encryption for one block
16 * provides the salt for the suceeding block.
18 * Restrictions: The buffer used to hold the encrypted result is
19 * statically allocated. (see MAX_PASS_LEN below). This is necessary,
20 * as the returned pointer points to "static data that are overwritten
21 * by each call", (XPG3: XSI System Interface + Headers pg 109), and
22 * this is a drop in replacement for crypt();
24 * Andy Phillips <atp@mssl.ucl.ac.uk>
28 * Max cleartext password length in segments of 8 characters this
29 * function can deal with (16 segments of 8 chars= max 128 character
33 #define MAX_PASS_LEN 16
34 #define SEGMENT_SIZE 8
36 #define KEYBUF_SIZE ((MAX_PASS_LEN*SEGMENT_SIZE)+SALT_SIZE)
37 #define ESEGMENT_SIZE 11
38 #define CBUF_SIZE ((MAX_PASS_LEN*ESEGMENT_SIZE)+SALT_SIZE+1)
40 static char *bigcrypt(const char *key, const char *salt)
42 static char dec_c2_cryptbuf[CBUF_SIZE]; /* static storage area */
44 unsigned long int keylen,n_seg,j;
45 char *cipher_ptr,*plaintext_ptr,*tmp_ptr,*salt_ptr;
46 char keybuf[KEYBUF_SIZE+1];
48 D(("called with key='%s', salt='%s'.", key, salt));
51 memset(keybuf, 0, KEYBUF_SIZE+1);
52 memset(dec_c2_cryptbuf, 0, CBUF_SIZE);
54 /* fill KEYBUF_SIZE with key */
55 strncpy(keybuf, key, KEYBUF_SIZE);
57 /* deal with case that we are doing a password check for a
58 conventially encrypted password: the salt will be
59 SALT_SIZE+ESEGMENT_SIZE long. */
60 if (strlen(salt) == (SALT_SIZE+ESEGMENT_SIZE))
61 keybuf[SEGMENT_SIZE] = '\0'; /* terminate password early(?) */
63 keylen = strlen(keybuf);
68 /* work out how many segments */
69 n_seg = 1 + ((keylen-1)/SEGMENT_SIZE);
72 if (n_seg > MAX_PASS_LEN)
73 n_seg = MAX_PASS_LEN; /* truncate at max length */
75 /* set up some pointers */
76 cipher_ptr = dec_c2_cryptbuf;
77 plaintext_ptr = keybuf;
79 /* do the first block with supplied salt */
80 tmp_ptr = crypt(plaintext_ptr,salt); /* libc crypt() */
82 /* and place in the static area */
83 strncpy(cipher_ptr, tmp_ptr, 13);
84 cipher_ptr += ESEGMENT_SIZE + SALT_SIZE;
85 plaintext_ptr += SEGMENT_SIZE; /* first block of SEGMENT_SIZE */
87 /* change the salt (1st 2 chars of previous block) - this was found
90 salt_ptr = cipher_ptr - ESEGMENT_SIZE;
92 /* so far this is identical to "return crypt(key, salt);", if
93 there is more than one block encrypt them... */
96 for (j=2; j <= n_seg; j++) {
98 tmp_ptr = crypt(plaintext_ptr, salt_ptr);
100 /* skip the salt for seg!=0 */
101 strncpy(cipher_ptr, (tmp_ptr+SALT_SIZE), ESEGMENT_SIZE);
103 cipher_ptr += ESEGMENT_SIZE;
104 plaintext_ptr += SEGMENT_SIZE;
105 salt_ptr = cipher_ptr - ESEGMENT_SIZE;
109 D(("key=|%s|, salt=|%s|\nbuf=|%s|\n", key, salt, dec_c2_cryptbuf));
111 /* this is the <NUL> terminated encrypted password */
113 return dec_c2_cryptbuf;