digest: add MD5-Crypt algo

[Ansuel]

Add MD5-Crypt algo to generare an hashed password entry to be used in shadow file.

The function will generate a random salt and return an MD5 hashed entry.

This follow the standard (and strange) way of generating an MD5-Crypt entry.

[Ansuel]

(context for this... ideally with this we should be able to replace the hack we have of manually calling passwd)

[jow-]

I think it would be simpler to wrap the libc crypt() instead:

#include <stdio.h>
#include <crypt.h>

int main() {
  char *password = "supersecret";
  char *setting = "$1$12345678"; // `$1$` selects MD5 algo, `12345678` are salt bytes
  char *secret = crypt(password, setting);
  
  printf("Crypt hash of %s is %s\n", password, secret);

  return 0;
}

I've been thinking about a unix module for a while which would bundle bindings for functions such as crypt(), getspnam(), getuid() etc.

In ucode you could then do:

import { crypt } from 'unix';

print("Hash: ", crypt("supersecret", "$1$12345678"), "\n");

[Ansuel]

@jow- yes i jumped and had some fun checking how the md5 crypt worked and then discovered that in theory crypt should be portable enough to be usable everywhere.

The main problem is generating the salt... I feel we should provide a shothand for that (there is no helper for that...)

[jow-]

We could allow the salt argument to be a two element array [algo, salt] and allow salt to be either a string (taken verbatim) or a number (generate that many random bytes):

crypt("plaintext", "$1$");  // md5, no salt
crypt("plaintext", "$1$12345678");  // md5, salt "12345678"
crypt("plaintext", [ 1, "12345678" ]);  // md5, salt "12345678"
crypt("plaintext", [ 1, 8 ]);  // md5, salt with 8 random bytes

Instead of a number for the algo we could also accept a symbolic name:

crypt("plaintext", [ "md5", "12345678" ]);  // md5, salt "12345678"
crypt("plaintext", [ "md5", 8 ]);  // md5, salt with 8 random bytes

And support the aliases documented in crypt(5)

[Ansuel]

@jow- yes that would be ideal. Any hint on that?

With that simple thing then I would do the extra step for adding md5-crypt in digest to generate a simple string.

(the pattern would be similar to how it's done currently for md5 sha1 sha256... as we would have to just define the type)