return supported hash algorithms

Question

i need a command or a script returning supported hashing algorithms (for hashing passwords) on a system, i mean algorithms can be used with pam.d configuration files or login.defs .

generally md5,bigcrypt,sha256, sha512 and blowfish are supported but i need to programmatically check if new algorithm is supported and determine it in my script.i checked /proc/crypto but is was too less than what i mentioned before

thanks

Answer 1

/proc/crypto is just a list of the algorithms that the kernel knows about; this has nothing to do with PAM.

There is no way to directly query PAM to find out what hashes it can support; it knows this internally, of course, but it is not exposed by any public API.

One thing you could do is use crypt and attempt to hash a pass with the various id types, essentially probing PAM (or more properly, probing libc's crypt, which PAM uses for shadowed passwords). Simple example:

#include <unistd.h>
#include <stdio.h>
#include <string>

bool test_crypt_method(const char* id)
   {
   const std::string salt =
      std::string("$") + id + "$" + "testsalt$";

   std::string crypt_result = ::crypt("password", salt.c_str());

   /*
   * If the hash ID is not supported, glibc unfortunately
   * then treats it as a old-style DES crypt rather than
   * failing; find this situation.
   */
   if(crypt_result.size() == 13 &&
      crypt_result[0] == '$' &&
      crypt_result.find('$', 1) == std::string::npos)
      return false;

   return true;
   }

int main()
   {
   if(test_crypt_method("1"))
      printf("md5 ");
   if(test_crypt_method("2a"))
      printf("blowfish ");
   if(test_crypt_method("4")) // test for false positives
      printf("undefined ");
   if(test_crypt_method("5"))
      printf("sha256 ");
   if(test_crypt_method("6"))
      printf("sha512 ");
   printf("\n");
   }