PWQUALITY(3) Libpwquality API Manual PWQUALITY(3)

pwquality - Documentation of the libpwquality API

#include <pwquality.h>
pwquality_settings_t *pwquality_default_settings(void);
void pwquality_free_settings(pwquality_settings_t *pwq);
int pwquality_read_config(pwquality_settings_t *pwq, const char *cfgfile,
       void **auxerror);
int pwquality_set_option(pwquality_settings_t *pwq, const char *option);
int pwquality_set_int_value(pwquality_settings_t *pwq, int setting, int value);
int pwquality_set_str_value(pwquality_settings_t *pwq, int setting,
       const char *value);
int pwquality_get_int_value(pwquality_settings_t *pwq, int setting, int *value);
int pwquality_get_str_value(pwquality_settings_t *pwq, int setting, const char **value);
int pwquality_generate(pwquality_settings_t *pwq, int entropy_bits,
       char **password);
int pwquality_check(pwquality_settings_t *pwq, const char *password,
       const char *oldpassword, const char *user, void **auxerror);
const char *pwquality_strerror(char *buf, size_t len, int errcode, void *auxerror);

Function pwquality_default_settings() allocates and returns default pwquality settings to be used in other library calls. The allocated opaque structure has to be freed with the pwquality_free_settings() call.

The pwquality_read_config() parses the configuration file (if cfgfile is NULL then the default one). If auxerror is not NULL it also possibly returns auxiliary error information that must be passed into pwquality_strerror() function.

The library first tries to parse all *.conf configuration files from <cfgfile>.d directory if it exists. Order of parsing determines what values will be in effect - the latest wins.

Function pwquality_set_option() is useful for setting the options as configured on a pam module command line in form of opt=val.

Getter and setter functions for the individual integer and string setting values are: pwquality_set_int_value(), pwquality_set_str_value(), pwquality_get_int_value(), and pwquality_get_str_value(). In case of the string getter the caller must copy the string before another calls that can manipulate the pwq settings object.

The pwquality_generate() function generates a random password of entropy_bits entropy and checks it according to the settings. The *password is allocated on the heap by the library. The entropy_bits value is adjusted to fit within the PWQ_MIN_ENTROPY_BITS and PWQ_MAX_ENTROPY_BITS range before generating a password.

The pwquality_check() function checks the password according to the settings. It returns either score (value between 0 and 100), negative error number, and possibly also auxiliary error information that must be passed into the pwquality_strerror() function. The oldpassword is optional and can be NULL. The user is used for checking the password against the user name and potentially other passwd(5) information and can be NULL. The auxerror can be NULL - in that case the auxiliary error information is not returned. However if it is non-NULL not passing the returned *auxerror into pwquality_strerror() can lead to memory leaks.

The score of a password depends on the value of the setting PWQ_SETTING_MIN_LENGTH. If it is set higher, the score for the same passwords will be lower.

Function pwquality_strerror() translates the errcode and auxerror auxiliary data into a localized text message. If buf is NULL the function uses an internal static buffer which makes the function non-reentrant in that case. The returned pointer is not guaranteed to point to the buf. The function deallocates eventual auxerror data passed into it, thus it must not be called twice with the same auxerror data.

In general the functions which return int return 0 as success value and negative values as concrete PWQ_ERROR error code. pwquality_strerror() does not allocate data and so it cannot fail.

The returned positive or zero score from pwquality_check() should not be used for rejection of passwords, it should be used only as approximate indicator of entropy present in the password with values such as 0-30 being low, 30-60 medium, and 60-100 high.

Typical use of the libpwquality API:

#include <pwquality.h>
       pwquality_settings_t *pwq;
       int rv;
       void *auxerror;
       char buf[PWQ_MAX_ERROR_MESSAGE_LEN];
       pwq = pwquality_default_settings();
       if (pwq == NULL) {
               fprintf(stderr, "Error: %s\n", pwquality_strerror(buf, sizeof(buf), PWQ_ERROR_MEM_ALLOC, NULL));
               return -1;

       if ((rv=pwquality_read_config(pwq, NULL, &auxerror)) != 0) {
               fprintf(stderr, "Error: %s\n", pwquality_strerror(buf, sizeof(buf), rv, auxerror));
               return -1;

       rv = pwquality_check(pwq, buf, NULL, user, &auxerror);
       if (rv >= 0) {
               fprintf(stderr, "Password entropy score is: %d\n", rv);
       } else {
               fprintf(stderr, "Password is rejected with error: %s\n", pwquality_strerror(buf, sizeof(buf), rv, auxerror));


Tomas Mraz <>

2021-04-01 Red Hat, Inc.