Encoding a Password

When Directory Server calls a password storage scheme plug-in encode function, it passes that function an input password char * and expects an encoded password char * in return. The prototype for the example encode function, xorenc(), is as follows:

static char * xorenc(char * pwd);

Allocate space for the encoded password with slapi_ch_malloc() rather than regular malloc(). Directory Server can then terminate with an “out of memory” message if allocation fails memory with slapi_ch_free().

By convention, you prefix the encoded password with the name of the password storage scheme, enclosed in braces, { and }. In other words, the example plug-in is called XOR.

The name is declared in the example:

static char * name = "XOR";   /* Storage scheme name */

You return encoded strings prefixed with {XOR}. You also register the name with Directory Server.

Example 12–1 Encoding a userPassword Value (testpwdstore.c)

#include "slapi-plugin.h"

static char * name           ="XOR";   /* Storage scheme name */

#define PREFIX_START '{'
#define PREFIX_END   '}'

static char *
xorenc(char * pwd)
{
    char * tmp    = NULL;              /* Used for encoding   */
    char * head   = NULL;              /* Encoded password    */
    char * cipher = NULL;              /* Prefix, then pwd    */
    int i, len;
  
    /* Allocate space to build the encoded password           */
    len = strlen(pwd);
    tmp = slapi_ch_malloc(len + 1);
    if (tmp == NULL) return NULL;

    memset(tmp, '\0', len + 1);
    head = tmp;

    /* Encode. This example is not secure by any means.       */
    for (i = 0; i < len; i++, pwd++, tmp++) *tmp = *pwd ^ 42;
  
    /* Add the prefix to the cipher                           */
    if (tmp != NULL) {
        cipher = slapi_ch_malloc(3 + strlen(name) + strlen(head));
        if (cipher != NULL) {
            sprintf(cipher,"%c%s%c%s",PREFIX_START,name,PREFIX_END,head);
        }
    }
    slapi_ch_free((void **) &head);
  
    return (cipher);                   /* Server frees cipher */
}

Notice that you free only memory allocated for temporary use. Directory Server frees memory for the char * returned, not the plug-in. For details on slapi_ch_malloc() and slapi_ch_free(), see Chapter 16, Function Reference, Part I.