How do I generate a SALT in Java for Salted-Hash?
I've been looking around and the closest answer is : How to generate a random alpha-numeric string?
I want to follow this workflow according to this CrackStation tutorial:
To Store a Password
Generate a long random salt using a CSPRNG.
Prepend the salt to the password and hash it with a standard cryptographic hash function such as SHA256.
Save both the salt and the hash in the user's database record.
To Validate a Password
Retrieve the user's salt and hash from the database.
Prepend the salt to the given password and hash it using the same hash function.
Compare the hash of the given password with the hash from the database. If they match, the password is correct. Otherwise, the password is incorrect.
I don't know how to generate a SALT. I figured out how to generate a hash using the MessageDigest. I tried using SecureRandom but nextByte method produces garbled code.
Edit: I don't know which answer to choose, they're too complicated for me, I have decided to use jBCrypt; jBCript is easy to use, does all the complex stuff behind the scenes. so I'll let the community vote up for the best answer.
Inspired from this post and that post, I use this code to generate and verify hashed salted passwords. It only uses JDK provided classes, no external dependency.
The process is:
- you create a salt with
getNextSalt - you ask the user his password and use the
hashmethod to generate a salted and hashed password. The method returns abyte[]which you can save as is in a database with the salt - to authenticate a user, you ask his password, retrieve the salt and hashed password from the database and use the
isExpectedPasswordmethod to check that the details match
/**
* A utility class to hash passwords and check passwords vs hashed values. It uses a combination of hashing and unique
* salt. The algorithm used is PBKDF2WithHmacSHA1 which, although not the best for hashing password (vs. bcrypt) is
* still considered robust and <a href="https://security.stackexchange.com/a/6415/12614"> recommended by NIST </a>.
* The hashed value has 256 bits.
*/
public class Passwords {
private static final Random RANDOM = new SecureRandom();
private static final int ITERATIONS = 10000;
private static final int KEY_LENGTH = 256;
/**
* static utility class
*/
private Passwords() { }
/**
* Returns a random salt to be used to hash a password.
*
* @return a 16 bytes random salt
*/
public static byte[] getNextSalt() {
byte[] salt = new byte[16];
RANDOM.nextBytes(salt);
return salt;
}
/**
* Returns a salted and hashed password using the provided hash.<br>
* Note - side effect: the password is destroyed (the char[] is filled with zeros)
*
* @param password the password to be hashed
* @param salt a 16 bytes salt, ideally obtained with the getNextSalt method
*
* @return the hashed password with a pinch of salt
*/
public static byte[] hash(char[] password, byte[] salt) {
PBEKeySpec spec = new PBEKeySpec(password, salt, ITERATIONS, KEY_LENGTH);
Arrays.fill(password, Character.MIN_VALUE);
try {
SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
return skf.generateSecret(spec).getEncoded();
} catch (NoSuchAlgorithmException | InvalidKeySpecException e) {
throw new AssertionError("Error while hashing a password: " + e.getMessage(), e);
} finally {
spec.clearPassword();
}
}
/**
* Returns true if the given password and salt match the hashed value, false otherwise.<br>
* Note - side effect: the password is destroyed (the char[] is filled with zeros)
*
* @param password the password to check
* @param salt the salt used to hash the password
* @param expectedHash the expected hashed value of the password
*
* @return true if the given password and salt match the hashed value, false otherwise
*/
public static boolean isExpectedPassword(char[] password, byte[] salt, byte[] expectedHash) {
byte[] pwdHash = hash(password, salt);
Arrays.fill(password, Character.MIN_VALUE);
if (pwdHash.length != expectedHash.length) return false;
for (int i = 0; i < pwdHash.length; i++) {
if (pwdHash[i] != expectedHash[i]) return false;
}
return true;
}
/**
* Generates a random password of a given length, using letters and digits.
*
* @param length the length of the password
*
* @return a random password
*/
public static String generateRandomPassword(int length) {
StringBuilder sb = new StringBuilder(length);
for (int i = 0; i < length; i++) {
int c = RANDOM.nextInt(62);
if (c <= 9) {
sb.append(String.valueOf(c));
} else if (c < 36) {
sb.append((char) ('a' + c - 10));
} else {
sb.append((char) ('A' + c - 36));
}
}
return sb.toString();
}
}
You were right regarding how you want to generate salt i.e. its nothing but a random number. For this particular case it would protect your system from possible Dictionary attacks. Now, for the second problem what you could do is instead of using UTF-8 encoding you may want to use Base64. Here, is a sample for generating a hash. I am using Apache Common Codecs for doing the base64 encoding you may select one of your own
public byte[] generateSalt() {
SecureRandom random = new SecureRandom();
byte bytes[] = new byte[20];
random.nextBytes(bytes);
return bytes;
}
public String bytetoString(byte[] input) {
return org.apache.commons.codec.binary.Base64.encodeBase64String(input);
}
public byte[] getHashWithSalt(String input, HashingTechqniue technique, byte[] salt) throws NoSuchAlgorithmException {
MessageDigest digest = MessageDigest.getInstance(technique.value);
digest.reset();
digest.update(salt);
byte[] hashedBytes = digest.digest(stringToByte(input));
return hashedBytes;
}
public byte[] stringToByte(String input) {
if (Base64.isBase64(input)) {
return Base64.decodeBase64(input);
} else {
return Base64.encodeBase64(input.getBytes());
}
}
Here is some additional reference of the standard practice in password hashing directly from OWASP
Another version using SHA-3, I am using bouncycastle:
The interface:
public interface IPasswords {
/**
* Generates a random salt.
*
* @return a byte array with a 64 byte length salt.
*/
byte[] getSalt64();
/**
* Generates a random salt
*
* @return a byte array with a 32 byte length salt.
*/
byte[] getSalt32();
/**
* Generates a new salt, minimum must be 32 bytes long, 64 bytes even better.
*
* @param size the size of the salt
* @return a random salt.
*/
byte[] getSalt(final int size);
/**
* Generates a new hashed password
*
* @param password to be hashed
* @param salt the randomly generated salt
* @return a hashed password
*/
byte[] hash(final String password, final byte[] salt);
/**
* Expected password
*
* @param password to be verified
* @param salt the generated salt (coming from database)
* @param hash the generated hash (coming from database)
* @return true if password matches, false otherwise
*/
boolean isExpectedPassword(final String password, final byte[] salt, final byte[] hash);
/**
* Generates a random password
*
* @param length desired password length
* @return a random password
*/
String generateRandomPassword(final int length);
}
The implementation:
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.Validate;
import org.apache.log4j.Logger;
import org.bouncycastle.jcajce.provider.digest.SHA3;
import java.io.Serializable;
import java.io.UnsupportedEncodingException;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
public final class Passwords implements IPasswords, Serializable {
/*serialVersionUID*/
private static final long serialVersionUID = 8036397974428641579L;
private static final Logger LOGGER = Logger.getLogger(Passwords.class);
private static final Random RANDOM = new SecureRandom();
private static final int DEFAULT_SIZE = 64;
private static final char[] symbols;
static {
final StringBuilder tmp = new StringBuilder();
for (char ch = '0'; ch <= '9'; ++ch) {
tmp.append(ch);
}
for (char ch = 'a'; ch <= 'z'; ++ch) {
tmp.append(ch);
}
symbols = tmp.toString().toCharArray();
}
@Override public byte[] getSalt64() {
return getSalt(DEFAULT_SIZE);
}
@Override public byte[] getSalt32() {
return getSalt(32);
}
@Override public byte[] getSalt(int size) {
final byte[] salt;
if (size < 32) {
final String message = String.format("Size < 32, using default of: %d", DEFAULT_SIZE);
LOGGER.warn(message);
salt = new byte[DEFAULT_SIZE];
} else {
salt = new byte[size];
}
RANDOM.nextBytes(salt);
return salt;
}
@Override public byte[] hash(String password, byte[] salt) {
Validate.notNull(password, "Password must not be null");
Validate.notNull(salt, "Salt must not be null");
try {
final byte[] passwordBytes = password.getBytes("UTF-8");
final byte[] all = ArrayUtils.addAll(passwordBytes, salt);
SHA3.DigestSHA3 md = new SHA3.Digest512();
md.update(all);
return md.digest();
} catch (UnsupportedEncodingException e) {
final String message = String
.format("Caught UnsupportedEncodingException e: <%s>", e.getMessage());
LOGGER.error(message);
}
return new byte[0];
}
@Override public boolean isExpectedPassword(final String password, final byte[] salt, final byte[] hash) {
Validate.notNull(password, "Password must not be null");
Validate.notNull(salt, "Salt must not be null");
Validate.notNull(hash, "Hash must not be null");
try {
final byte[] passwordBytes = password.getBytes("UTF-8");
final byte[] all = ArrayUtils.addAll(passwordBytes, salt);
SHA3.DigestSHA3 md = new SHA3.Digest512();
md.update(all);
final byte[] digest = md.digest();
return Arrays.equals(digest, hash);
}catch(UnsupportedEncodingException e){
final String message =
String.format("Caught UnsupportedEncodingException e: <%s>", e.getMessage());
LOGGER.error(message);
}
return false;
}
@Override public String generateRandomPassword(final int length) {
if (length < 1) {
throw new IllegalArgumentException("length must be greater than 0");
}
final char[] buf = new char[length];
for (int idx = 0; idx < buf.length; ++idx) {
buf[idx] = symbols[RANDOM.nextInt(symbols.length)];
}
return shuffle(new String(buf));
}
private String shuffle(final String input){
final List<Character> characters = new ArrayList<Character>();
for(char c:input.toCharArray()){
characters.add(c);
}
final StringBuilder output = new StringBuilder(input.length());
while(characters.size()!=0){
int randPicker = (int)(Math.random()*characters.size());
output.append(characters.remove(randPicker));
}
return output.toString();
}
}
The test cases:
public class PasswordsTest {
private static final Logger LOGGER = Logger.getLogger(PasswordsTest.class);
@Before
public void setup(){
BasicConfigurator.configure();
}
@Test
public void testGeSalt() throws Exception {
IPasswords passwords = new Passwords();
final byte[] bytes = passwords.getSalt(0);
int arrayLength = bytes.length;
assertThat("Expected length is", arrayLength, is(64));
}
@Test
public void testGeSalt32() throws Exception {
IPasswords passwords = new Passwords();
final byte[] bytes = passwords.getSalt32();
int arrayLength = bytes.length;
assertThat("Expected length is", arrayLength, is(32));
}
@Test
public void testGeSalt64() throws Exception {
IPasswords passwords = new Passwords();
final byte[] bytes = passwords.getSalt64();
int arrayLength = bytes.length;
assertThat("Expected length is", arrayLength, is(64));
}
@Test
public void testHash() throws Exception {
IPasswords passwords = new Passwords();
final byte[] hash = passwords.hash("holacomoestas", passwords.getSalt64());
assertThat("Array is not null", hash, Matchers.notNullValue());
}
@Test
public void testSHA3() throws UnsupportedEncodingException {
SHA3.DigestSHA3 md = new SHA3.Digest256();
md.update("holasa".getBytes("UTF-8"));
final byte[] digest = md.digest();
assertThat("expected digest is:",digest,Matchers.notNullValue());
}
@Test
public void testIsExpectedPasswordIncorrect() throws Exception {
String password = "givemebeer";
IPasswords passwords = new Passwords();
final byte[] salt64 = passwords.getSalt64();
final byte[] hash = passwords.hash(password, salt64);
//The salt and the hash go to database.
final boolean isPasswordCorrect = passwords.isExpectedPassword("jfjdsjfsd", salt64, hash);
assertThat("Password is not correct", isPasswordCorrect, is(false));
}
@Test
public void testIsExpectedPasswordCorrect() throws Exception {
String password = "givemebeer";
IPasswords passwords = new Passwords();
final byte[] salt64 = passwords.getSalt64();
final byte[] hash = passwords.hash(password, salt64);
//The salt and the hash go to database.
final boolean isPasswordCorrect = passwords.isExpectedPassword("givemebeer", salt64, hash);
assertThat("Password is correct", isPasswordCorrect, is(true));
}
@Test
public void testGenerateRandomPassword() throws Exception {
IPasswords passwords = new Passwords();
final String randomPassword = passwords.generateRandomPassword(10);
LOGGER.info(randomPassword);
assertThat("Random password is not null", randomPassword, Matchers.notNullValue());
}
}
pom.xml (only dependencies):
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.testng</groupId>
<artifactId>testng</artifactId>
<version>6.1.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.hamcrest</groupId>
<artifactId>hamcrest-all</artifactId>
<version>1.3</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>org.bouncycastle</groupId>
<artifactId>bcprov-jdk15on</artifactId>
<version>1.51</version>
<type>jar</type>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.3.2</version>
</dependency>
</dependencies>