password - ¿Cómo puedo generar un SALT en Java para Salted-Hash?

salt length

Question

He estado mirando a mi alrededor y la respuesta más cercana es: ¿cómo generar una cadena alfanumérica aleatoria?

Quiero seguir este flujo de trabajo de acuerdo con este tutorial de CrackStation :

Para almacenar una contraseña

1. Genere una sal aleatoria larga usando un CSPRNG.

2. Anteponga la sal a la contraseña y córtela con una función hash criptográfica estándar como SHA256.

3. Guarde tanto la sal como el hash en el registro de la base de datos del usuario.

Para validar una contraseña

1. Recupere la sal y el hash del usuario de la base de datos.

2. Prefiera la sal a la contraseña dada y córtela usando la misma función hash.

3. Compare el hash de la contraseña dada con el hash de la base de datos. Si coinciden, la contraseña es correcta. De lo contrario, la contraseña es incorrecta.

No sé cómo generar un SALT. Descubrí cómo generar un hash usando el MessageDigest. Intenté usar SecureRandom pero el método nextByte produce código ilegible.

Editar: No sé qué respuesta elegir, son demasiado complicadas para mí, he decidido usar jBCrypt; jBCript es fácil de usar, hace todo lo complejo detrás de escena. así que dejaré que la comunidad vote por la mejor respuesta.

Answer 1

Inspirado en esta publicación y esa publicación , utilizo este código para generar y verificar contraseñas desvainadas en hash. Solo usa clases proporcionadas por JDK, sin dependencia externa.

El proceso es:

• creas una sal con getNextSalt
• le pregunta al usuario su contraseña y utiliza el método hash para generar una contraseña salada y hash. El método devuelve un byte[] que puede guardar como está en una base de datos con la sal
• para autenticar a un usuario, solicite su contraseña, recupere la contraseña saliente y hash de la base de datos y use el método isExpectedPassword para verificar que los detalles coincidan

/**
* 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();
}
}

Answer 2

Otra versión que usa SHA-3, estoy usando bouncycastle:

La interfaz:

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);
}

La implementación:

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();
}
}

Los casos de prueba:

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 (solo dependencias):

<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>

Answer 3

Tenías razón con respecto a cómo quieres generar sal, es decir, no es más que un número aleatorio. Para este caso particular, protegería su sistema de posibles ataques de diccionario. Ahora, para el segundo problema, lo que podrías hacer es usar la base UTF-8 en lugar de utilizar la codificación UTF-8. Aquí, hay una muestra para generar un hash. Estoy usando Apache Common Codecs para hacer la codificación base64, puede seleccionar uno de los suyos

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());
}
}

Aquí hay alguna referencia adicional de la práctica estándar en el uso de contraseñas directamente desde OWASP