SV.HASH.NO_SALT
Use of a one-way cryptographic hash without a salt
This error is reported when a one-way cryptographic hash function is applied to a single piece of input data without salt being added.
Vulnerability and risk
If software stores one-way cryptographic hashes calculated for user passwords, appending or prepending a unique salt to each password is recommended; so if two users have the same password, the hashes will be different.
If an attacker gains access to the hashes, the lack of a salt makes it easier to guess multiple user passwords.
Vulnerable code example
1 /*
2 * Adds a new user; stores login and password hash.
3 */
4 public void addUser(String login, byte[] password) {
5 try {
6 MessageDigest md = MessageDigest.getInstance("MD5");
7
md.update(password); // < -- calculate hash for the password
8 byte[] hash = md.digest();
9 storeHashString(login, Hex.encodeHexString(hash));
10 } catch (NoSuchAlgorithmException e) {
11 throw new IllegalStateException(e);
12 }
13 }
14
15 /*
16 * Validates user login information. Returns true if user exists, and
17 entered password hash matches stored password hash;
18 * otherwise returns false.
19 */
20 public boolean login(String login, byte[] password) {
21 try {
22 String storedHash = readHashString(login);
23 if (storedHash != null) {
24 MessageDigest md = MessageDigest.getInstance("MD5");
25
md.update(password); // < -- calculate hash for the password
26 byte[] hash = md.digest();
27 return MessageDigest.isEqual(hash, Hex.decodeHex(storedHash.toCharArray()));
28 } else {
29 return false;
30 }
31 } catch (NoSuchAlgorithmException | DecoderException e) {
32 throw new IllegalStateException(e);
33 }
34 }
35
36 . . .
37
38 hashManager.addUser("Alice", "changeit".getBytes());
39 hashManager.addUser("Bob", "changeit".getBytes());
In this example, both users – “Alice” and “Bob” have password “changeit”; and both stored hashes are “b91cd1a54781790beaa2baf741fa6789”. Then, if an attacker steals the password hashes table, he can easily reverse “b91cd1a54781790beaa2baf741fa6789” to “changeit” using a dictionary.
Fixed code example
1 /*
2 * Adds a new user; stores login and "salt:hash".
3 */
4 public void addUser(String login, byte[] password) {
5 try {
6 byte[] salt = new byte[16];
7 secureRandom.nextBytes(salt);
8 MessageDigest md = MessageDigest.getInstance("MD5");
9
md.update(salt); // use random salt
10
md.update(password); // and password
11 byte[] hash = md.digest();
12 storeHashString(login, Hex.encodeHexString(salt) + ":" + Hex.encodeHexString(hash));
13 } catch (NoSuchAlgorithmException e) {
14 throw new IllegalStateException(e);
15 }
16 }
17
18 /*
19 * Validates user login information. Returns true if user exists, and
20 entered password matches stored "salt:hash"; otherwise returns false.
21 */
22 public boolean login(String login, byte[] password) {
23 try {
24 String storedSaltAndHash = readHashString(login);
25 if (storedSaltAndHash != null) {
26 String[] saltAndHash = storedSaltAndHash.split(":");
27 if (saltAndHash.length != 2) {
28 throw new IllegalStateException("Expected salt:hash string");
29 }
30 MessageDigest md = MessageDigest.getInstance("MD5");
31
md.update(Hex.decodeHex(saltAndHash[0].toCharArray())); // use stored salt
32
md.update(password);
33 byte[] hash = md.digest();
34 return MessageDigest.isEqual(hash, Hex.decodeHex(saltAndHash[1].toCharArray()));
35 } else {
36 return false;
37 }
38 } catch (NoSuchAlgorithmException | DecoderException e) {
39 throw new IllegalStateException(e);
40 }
41 }
42
43 . . .
44
45 hashManager.addUser("Alice", "changeit".getBytes());
46 hashManager.addUser("Bob", "changeit".getBytes());
Alice -> 03c016ca60ee8c53aa8f24301a08ec27:de88b6fc874d83eb30aa9020f431bde3 Bob -> e2eafef8be75cd58b7ed598ddb37e128:4bc3b11a2bf5854b66543f8ba9ffa2c6
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