Use of a One-Way Hash without a Salt

Description

Background

In cryptography, salt refers to some random addition of data to an input before hashing to make dictionary attacks more difficult.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In both of these examples, a user is logged in if their given password matches a stored password:

unsigned char *check_passwd(char *plaintext) {
  ctext = simple_digest("sha1",plaintext,strlen(plaintext), ... );
  //Login if hash matches stored hash
  if (equal(ctext, secret_password())) {
    login_user();
  }
}

String plainText = new String(plainTextIn);
MessageDigest encer = MessageDigest.getInstance("SHA");
encer.update(plainTextIn);
byte[] digest = password.digest();
//Login if hash matches stored hash
if (equal(digest,secret_password())) {
  login_user();
}

This code relies exclusively on a password mechanism (CWE-309) using only one factor of authentication (CWE-308). If an attacker can steal or guess a user's password, they are given full access to their account. Note this code also uses SHA-1, which is a weak hash (CWE-328). It also does not use a salt (CWE-759).

Example Two

In this example, a new user provides a new username and password to create an account. The program hashes the new user's password then stores it in a database.

def storePassword(userName,Password):
  hasher = hashlib.new('md5')
  hasher.update(Password)
  hashedPassword = hasher.digest()

  # UpdateUserLogin returns True on success, False otherwise
  return updateUserLogin(userName,hashedPassword)

While it is good to avoid storing a cleartext password, the program does not provide a salt to the hashing function, thus increasing the chances of an attacker being able to reverse the hash and discover the original password if the database is compromised.

Fixing this is as simple as providing a salt to the hashing function on initialization:

def storePassword(userName,Password):
  hasher = hashlib.new('md5',b'SaltGoesHere')
  hasher.update(Password)
  hashedPassword = hasher.digest()

  # UpdateUserLogin returns True on success, False otherwise
  return updateUserLogin(userName,hashedPassword)

Note that regardless of the usage of a salt, the md5 hash is no longer considered secure, so this example still exhibits CWE-327.

See Also