Cada aplicació de programari requereix un nom d'usuari i una contrasenya per autenticar l'usuari vàlid. Un nom d'usuari pot ser com un identificador de correu electrònic o només una combinació de caràcters. Però quan es crea una contrasenya, cal tenir molta cura. Perquè qualsevol persona amb credencials vàlides pot entrar al sistema i accedir a la informació.
Necessitat de xifrar una contrasenya
Quan un usuari estableix la seva contrasenya, s'emmagatzema a la base de dades com a text sense format. Emmagatzemar el text sense format tal com està a la base de dades no és gens segur. Els pirates informàtics poden trencar el sistema i robar les contrasenyes de la base de dades.
Per garantir la seguretat de la contrasenya de l'usuari, aquesta es xifra mitjançant diferents tècniques de xifratge. Mitjançant diverses tècniques de xifratge, la contrasenya de text sense format s'emmagatzema en forma xifrada a la base de dades. Hi ha molts mètodes que es poden utilitzar per xifrar la contrasenya. Però el hash és una de les tècniques de xifratge més populars.
Tècniques de hash segur de Java
El valor hash xifrat es genera mitjançant determinats algorismes a la contrasenya de text sense format proporcionada per l'usuari. La programació Java admet diverses tècniques hashing per xifrar una contrasenya.
Tècnica hashing MD5
L'MD5 (Message Digest) és un algorisme de hashing molt popular. És una funció hash criptogràfica que genera un valor hash de 128 bits. Aquest algorisme es defineix al paquet java.security a la programació Java.
PassEncTech1.java
abstracció en java
import java.security.NoSuchAlgorithmException; import java.security.MessageDigest; public class PassEncTech1 { /* Driver Code */ public static void main(String[] args) { /* Plain-text password initialization. */ String password = 'myPassword'; String encryptedpassword = null; try { /* MessageDigest instance for MD5. */ MessageDigest m = MessageDigest.getInstance('MD5'); /* Add plain-text password bytes to digest using MD5 update() method. */ m.update(password.getBytes()); /* Convert the hash value into bytes */ byte[] bytes = m.digest(); /* The bytes array has bytes in decimal form. Converting it into hexadecimal format. */ StringBuilder s = new StringBuilder(); for(int i=0; i <bytes.length ;i++) { s.append(integer.tostring((bytes[i] & 0xff) + 0x100, 16).substring(1)); } * complete hashed password in hexadecimal format encryptedpassword="s.toString();" catch (nosuchalgorithmexception e) e.printstacktrace(); display the unencrypted and encrypted passwords. system.out.println('plain-text password: ' password); system.out.println('encrypted using md5: encryptedpassword); < pre> <p> <strong>Output:</strong> </p> <pre> Plain-text password: myPassword Encrypted password using MD5: deb1536f480475f7d593219aa1afd74c </pre> <p>The above code shows the implementation of <strong> <em>MessageDigest</em> </strong> class in <strong> <em>java.security</em> </strong> package. The MD5 returns a byte array that needs to be converted into a readable hexadecimal format.</p> <p>The MD5 hashing technique is easy and fast to implement but it is also prone to brute force attacks or dictionary attacks.</p> <h3>SHA256</h3> <p>SHA is the Secure Hash Algorithm. It uses a cryptographic function that takes up the 32-bit plain-text password and converts it into a fixed size 256-bit hash value. This hashing technique is implemented using the MessageDiagest class of java.security package.</p> <p>It is a one-way encryption technique. Once the passphrase is encrypted it cannot be decrypted back.</p> <p> <strong>PassEncTech2.java</strong> </p> <pre> import java.math.BigInteger; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class PassEncTech2 { public static byte[] getSHA(String input) throws NoSuchAlgorithmException { /* MessageDigest instance for hashing using SHA256 */ MessageDigest md = MessageDigest.getInstance('SHA-256'); /* digest() method called to calculate message digest of an input and return array of byte */ return md.digest(input.getBytes(StandardCharsets.UTF_8)); } public static String toHexString(byte[] hash) { /* Convert byte array of hash into digest */ BigInteger number = new BigInteger(1, hash); /* Convert the digest into hex value */ StringBuilder hexString = new StringBuilder(number.toString(16)); /* Pad with leading zeros */ while (hexString.length() <32) { hexstring.insert(0, '0'); } return hexstring.tostring(); * driver code public static void main(string args[]) try string string1="myPassword" ; system.out.println('
' + ' : tohexstring(getsha(string1))); string2="hashtrial" tohexstring(getsha(string2))); catch (nosuchalgorithmexception e) system.out.println('exception thrown for incorrect algorithm: e); < pre> <p> <strong>Output:</strong> </p> <pre> myPassword : 76549b827ec46e705fd03831813fa52172338f0dfcbd711ed44b81a96dac51c6 hashtrial : d3e3224a59d69e9a000f1ce6782cb6a8be1eb3155610ff41bffbcbc95adc5d7 </pre> <p>The above code uses the instance of <strong> <em>MessageDigest</em> </strong> class to generate a hash for <strong> <em>SHA256</em> </strong> . The SHA256 returns a byte array that needs to be converted into a readable hexadecimal format. And lastly, the encrypted hash value is displayed.</p> <h3>SHA512 MD5 Hashing Technique</h3> <p>SHA512 uses a cryptographic function that takes up the 64-bit plain-text password and converts it into a fixed size 512-bit hash value. This hashing technique is also implemented using the MessageDiagest class of java.security package.</p> <p> <strong>PassEncTech2.java</strong> </p> <pre> import java.math.BigInteger; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class PassEncTech2 { public static byte[] getSHA(String input) throws NoSuchAlgorithmException { /* MessageDigest instance for hashing using SHA512*/ MessageDigest md = MessageDigest.getInstance('SHA-512'); /* digest() method called to calculate message digest of an input and return array of byte */ return md.digest(input.getBytes(StandardCharsets.UTF_8)); } public static String toHexString(byte[] hash) { /* Convert byte array of hash into digest */ BigInteger number = new BigInteger(1, hash); /* Convert the digest into hex value */ StringBuilder hexString = new StringBuilder(number.toString(16)); /* Pad with leading zeros */ while (hexString.length() <32) { hexstring.insert(0, '0'); } return hexstring.tostring(); * driver code public static void main(string args[]) try string string1="myPassword" ; system.out.println('
' + ' : tohexstring(getsha(string1))); string2="hashtrial" tohexstring(getsha(string2))); catch (nosuchalgorithmexception e) system.out.println('exception thrown for incorrect algorithm: e); < pre> <p> <strong>Output:</strong> </p> <pre> myPassword : 450ad03db9395dfccb5e03066fd7f16cfba2b61e23d516373714471459052ec90a9a4bf3a151e600ea8aaed36e3b8c21a3d38ab1705839749d130da4380f1448 hashtrial : 9520ea1a8d60d23334e6d59acebd587de6fec1e53db5836f467096c540ae60f7c85e9fbc90856dee9d6563609b8786b03b47892af0bad44bdcab2206f22df5cb </pre> <p>The above code uses the instance of <strong> <em>MessageDigest</em> </strong> class to generate a hash for <strong> <em>SHA512</em> </strong> . The SHA512 returns a byte array that needs to be converted into a readable hexadecimal format. And lastly, the encrypted hash value is displayed.</p> <h3>Password-Based Encryption using Salt and Base64:</h3> <p>The password-based encryption technique uses plain text passwords and salt values to generate a hash value. And the hash value is then encoded as a Base64 string. Salt value contains random data generated using an instance of Random class from java.util package.</p> <p>The following program demonstrates password encryption using salt and base64.</p> <p> <strong>PassEncTech4.java</strong> </p> <pre> import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.security.spec.InvalidKeySpecException; import java.util.Arrays; import java.util.Base64; import java.util.Random; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.PBEKeySpec; public class PassEncTech4 { /* Driver Code */ public static void main(String[] args) { /* Plain text Password. */ String password = 'myNewPass123'; /* generates the Salt value. It can be stored in a database. */ String saltvalue = PassBasedEnc.getSaltvalue(30); /* generates an encrypted password. It can be stored in a database.*/ String encryptedpassword = PassBasedEnc.generateSecurePassword(password, saltvalue); /* Print out plain text password, encrypted password and salt value. */ System.out.println('Plain text password = ' + password); System.out.println('Secure password = ' + encryptedpassword); System.out.println('Salt value = ' + saltvalue); /* verify the original password and encrypted password */ Boolean status = PassBasedEnc.verifyUserPassword(password,encryptedpassword,saltvalue); if(status==true) System.out.println('Password Matched!!'); else System.out.println('Password Mismatched'); } } class PassBasedEnc { /* Declaration of variables */ private static final Random random = new SecureRandom(); private static final String characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; private static final int iterations = 10000; private static final int keylength = 256; /* Method to generate the salt value. */ public static String getSaltvalue(int length) { StringBuilder finalval = new StringBuilder(length); for (int i = 0; i <length; i++) { finalval.append(characters.charat(random.nextint(characters.length()))); } return new string(finalval); * method to generate the hash value public static byte[] hash(char[] password, salt) pbekeyspec spec="new" pbekeyspec(password, salt, iterations, keylength); arrays.fill(password, character.min_value); try secretkeyfactory skf="SecretKeyFactory.getInstance('PBKDF2WithHmacSHA1');" skf.generatesecret(spec).getencoded(); catch (nosuchalgorithmexception | invalidkeyspecexception e) throw assertionerror('error while hashing a password: ' + e.getmessage(), e); finally spec.clearpassword(); encrypt password using original and salt value. string generatesecurepassword(string finalval="null;" securepassword="hash(password.toCharArray()," salt.getbytes()); finalval; verify if both matches or not boolean verifyuserpassword(string providedpassword, securedpassword, secure with same newsecurepassword="generateSecurePassword(providedPassword," salt); check two passwords are equal < pre> <p> <strong>Output:</strong> </p> <pre> Plain text password = myNewPass123 Secure password = sA0jNGQTrAfMUiqrB++bMKTU55ThdFCl16ZZTIXwD2M= Salt value = n7d9MPQFXxDqzT6onmong3hQt8Nyko Password Matched!! </pre> <p>In the above code, two classes are defined.</p> <ol class="points"> <li>The class <strong> <em>PassEncTech4</em> </strong> contains the driver code for the program. It generates a salt value and encrypted password using the given plain-text password. And verifies them using the value returned by the <strong> <em>verifyUserPassword() </em> </strong> </li> <li>In the class <strong> <em>PassBasedEnc, </em> </strong> 4 methods are defined. The first method is <strong> <em>getSaltvalue()</em> </strong> which generates the value using <strong> <em>Random</em> </strong> class from <strong> <em>util</em> </strong> package. Then <strong> <em>hash()</em> </strong> is defined that has a return type of byte array. The <strong> <em>generateSecurePassword() </em> </strong> uses plain-text password and salt value with the <strong> <em>hash()</em> </strong> method. And lastly, the two passwords are matched using the <strong> <em>verifyUserPassword()</em> </strong> method.</li> </ol> <h2>Techniques for Cracking the Hash</h2> <p>A hash value is prone to different kinds of attacks by attackers. Some of them are mentioned below,</p> <ol class="points"> <tr><td>Brute force attack:</td> In the brute force attack, the attacker submits multiple combinations of passphrases or passwords in the hope that one of the combinations will match and he can enter into the system. <br> To avoid this kind of attack the passphrase should use a combination of alphabets, numbers and symbols. Another way is to set a fixed number of invalid attempts and after that ask for human verification like a captcha. </tr><tr><td>Dictionary attack:</td> Dictionary attack is an enhanced version of brute force attack. In this technique, the encrypted cipher is tried to be decrypted using multiple possibilities, like the words in a dictionary. </tr><tr><td>Rainbow tables:</td> The technique is about a rainbow table that is precomputed table for reversing the cryptographic hash functions. The rainbow tables are used to discover the plain text passwords up to a certain length and a limited number of characters. So it uses a side-loop table in order to reduce the storage usage and increase the speed of attack. </tr></ol> <hr></length;></pre></32)></pre></32)></pre></bytes.length> El codi anterior mostra la implementació de Resum de missatges classe a java.security paquet. L'MD5 retorna una matriu de bytes que s'ha de convertir en un format hexadecimal llegible.
python converteix bytes en cadena
La tècnica hashing MD5 és fàcil i ràpida d'implementar, però també és propensa a atacs de força bruta o atacs de diccionari.
SHA256
SHA és l'algoritme de hash segur. Utilitza una funció criptogràfica que ocupa la contrasenya de text sense format de 32 bits i la converteix en un valor hash de mida fixa de 256 bits. Aquesta tècnica hash s'implementa mitjançant la classe MessageDiagest del paquet java.security.
És una tècnica de xifratge unidireccional. Un cop xifrada la contrasenya, no es pot tornar a desxifrar.
PassEncTech2.java
import java.math.BigInteger; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class PassEncTech2 { public static byte[] getSHA(String input) throws NoSuchAlgorithmException { /* MessageDigest instance for hashing using SHA256 */ MessageDigest md = MessageDigest.getInstance('SHA-256'); /* digest() method called to calculate message digest of an input and return array of byte */ return md.digest(input.getBytes(StandardCharsets.UTF_8)); } public static String toHexString(byte[] hash) { /* Convert byte array of hash into digest */ BigInteger number = new BigInteger(1, hash); /* Convert the digest into hex value */ StringBuilder hexString = new StringBuilder(number.toString(16)); /* Pad with leading zeros */ while (hexString.length() <32) { hexstring.insert(0, \'0\'); } return hexstring.tostring(); * driver code public static void main(string args[]) try string string1="myPassword" ; system.out.println(\'
\' + \' : tohexstring(getsha(string1))); string2="hashtrial" tohexstring(getsha(string2))); catch (nosuchalgorithmexception e) system.out.println(\'exception thrown for incorrect algorithm: e); < pre> <p> <strong>Output:</strong> </p> <pre> myPassword : 76549b827ec46e705fd03831813fa52172338f0dfcbd711ed44b81a96dac51c6 hashtrial : d3e3224a59d69e9a000f1ce6782cb6a8be1eb3155610ff41bffbcbc95adc5d7 </pre> <p>The above code uses the instance of <strong> <em>MessageDigest</em> </strong> class to generate a hash for <strong> <em>SHA256</em> </strong> . The SHA256 returns a byte array that needs to be converted into a readable hexadecimal format. And lastly, the encrypted hash value is displayed.</p> <h3>SHA512 MD5 Hashing Technique</h3> <p>SHA512 uses a cryptographic function that takes up the 64-bit plain-text password and converts it into a fixed size 512-bit hash value. This hashing technique is also implemented using the MessageDiagest class of java.security package.</p> <p> <strong>PassEncTech2.java</strong> </p> <pre> import java.math.BigInteger; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class PassEncTech2 { public static byte[] getSHA(String input) throws NoSuchAlgorithmException { /* MessageDigest instance for hashing using SHA512*/ MessageDigest md = MessageDigest.getInstance('SHA-512'); /* digest() method called to calculate message digest of an input and return array of byte */ return md.digest(input.getBytes(StandardCharsets.UTF_8)); } public static String toHexString(byte[] hash) { /* Convert byte array of hash into digest */ BigInteger number = new BigInteger(1, hash); /* Convert the digest into hex value */ StringBuilder hexString = new StringBuilder(number.toString(16)); /* Pad with leading zeros */ while (hexString.length() <32) { hexstring.insert(0, \'0\'); } return hexstring.tostring(); * driver code public static void main(string args[]) try string string1="myPassword" ; system.out.println(\'
\' + \' : tohexstring(getsha(string1))); string2="hashtrial" tohexstring(getsha(string2))); catch (nosuchalgorithmexception e) system.out.println(\'exception thrown for incorrect algorithm: e); < pre> <p> <strong>Output:</strong> </p> <pre> myPassword : 450ad03db9395dfccb5e03066fd7f16cfba2b61e23d516373714471459052ec90a9a4bf3a151e600ea8aaed36e3b8c21a3d38ab1705839749d130da4380f1448 hashtrial : 9520ea1a8d60d23334e6d59acebd587de6fec1e53db5836f467096c540ae60f7c85e9fbc90856dee9d6563609b8786b03b47892af0bad44bdcab2206f22df5cb </pre> <p>The above code uses the instance of <strong> <em>MessageDigest</em> </strong> class to generate a hash for <strong> <em>SHA512</em> </strong> . The SHA512 returns a byte array that needs to be converted into a readable hexadecimal format. And lastly, the encrypted hash value is displayed.</p> <h3>Password-Based Encryption using Salt and Base64:</h3> <p>The password-based encryption technique uses plain text passwords and salt values to generate a hash value. And the hash value is then encoded as a Base64 string. Salt value contains random data generated using an instance of Random class from java.util package.</p> <p>The following program demonstrates password encryption using salt and base64.</p> <p> <strong>PassEncTech4.java</strong> </p> <pre> import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.security.spec.InvalidKeySpecException; import java.util.Arrays; import java.util.Base64; import java.util.Random; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.PBEKeySpec; public class PassEncTech4 { /* Driver Code */ public static void main(String[] args) { /* Plain text Password. */ String password = 'myNewPass123'; /* generates the Salt value. It can be stored in a database. */ String saltvalue = PassBasedEnc.getSaltvalue(30); /* generates an encrypted password. It can be stored in a database.*/ String encryptedpassword = PassBasedEnc.generateSecurePassword(password, saltvalue); /* Print out plain text password, encrypted password and salt value. */ System.out.println('Plain text password = ' + password); System.out.println('Secure password = ' + encryptedpassword); System.out.println('Salt value = ' + saltvalue); /* verify the original password and encrypted password */ Boolean status = PassBasedEnc.verifyUserPassword(password,encryptedpassword,saltvalue); if(status==true) System.out.println('Password Matched!!'); else System.out.println('Password Mismatched'); } } class PassBasedEnc { /* Declaration of variables */ private static final Random random = new SecureRandom(); private static final String characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; private static final int iterations = 10000; private static final int keylength = 256; /* Method to generate the salt value. */ public static String getSaltvalue(int length) { StringBuilder finalval = new StringBuilder(length); for (int i = 0; i <length; i++) { finalval.append(characters.charat(random.nextint(characters.length()))); } return new string(finalval); * method to generate the hash value public static byte[] hash(char[] password, salt) pbekeyspec spec="new" pbekeyspec(password, salt, iterations, keylength); arrays.fill(password, character.min_value); try secretkeyfactory skf="SecretKeyFactory.getInstance('PBKDF2WithHmacSHA1');" skf.generatesecret(spec).getencoded(); catch (nosuchalgorithmexception | invalidkeyspecexception e) throw assertionerror(\'error while hashing a password: \' + e.getmessage(), e); finally spec.clearpassword(); encrypt password using original and salt value. string generatesecurepassword(string finalval="null;" securepassword="hash(password.toCharArray()," salt.getbytes()); finalval; verify if both matches or not boolean verifyuserpassword(string providedpassword, securedpassword, secure with same newsecurepassword="generateSecurePassword(providedPassword," salt); check two passwords are equal < pre> <p> <strong>Output:</strong> </p> <pre> Plain text password = myNewPass123 Secure password = sA0jNGQTrAfMUiqrB++bMKTU55ThdFCl16ZZTIXwD2M= Salt value = n7d9MPQFXxDqzT6onmong3hQt8Nyko Password Matched!! </pre> <p>In the above code, two classes are defined.</p> <ol class="points"> <li>The class <strong> <em>PassEncTech4</em> </strong> contains the driver code for the program. It generates a salt value and encrypted password using the given plain-text password. And verifies them using the value returned by the <strong> <em>verifyUserPassword() </em> </strong> </li> <li>In the class <strong> <em>PassBasedEnc, </em> </strong> 4 methods are defined. The first method is <strong> <em>getSaltvalue()</em> </strong> which generates the value using <strong> <em>Random</em> </strong> class from <strong> <em>util</em> </strong> package. Then <strong> <em>hash()</em> </strong> is defined that has a return type of byte array. The <strong> <em>generateSecurePassword() </em> </strong> uses plain-text password and salt value with the <strong> <em>hash()</em> </strong> method. And lastly, the two passwords are matched using the <strong> <em>verifyUserPassword()</em> </strong> method.</li> </ol> <h2>Techniques for Cracking the Hash</h2> <p>A hash value is prone to different kinds of attacks by attackers. Some of them are mentioned below,</p> <ol class="points"> <tr><td>Brute force attack:</td> In the brute force attack, the attacker submits multiple combinations of passphrases or passwords in the hope that one of the combinations will match and he can enter into the system. <br> To avoid this kind of attack the passphrase should use a combination of alphabets, numbers and symbols. Another way is to set a fixed number of invalid attempts and after that ask for human verification like a captcha. </tr><tr><td>Dictionary attack:</td> Dictionary attack is an enhanced version of brute force attack. In this technique, the encrypted cipher is tried to be decrypted using multiple possibilities, like the words in a dictionary. </tr><tr><td>Rainbow tables:</td> The technique is about a rainbow table that is precomputed table for reversing the cryptographic hash functions. The rainbow tables are used to discover the plain text passwords up to a certain length and a limited number of characters. So it uses a side-loop table in order to reduce the storage usage and increase the speed of attack. </tr></ol> <hr></length;></pre></32)></pre></32)> El codi anterior utilitza la instància de Resum de missatges classe per generar un hash SHA256 . El SHA256 retorna una matriu de bytes que s'ha de convertir en un format hexadecimal llegible. I, finalment, es mostra el valor hash xifrat.
SHA512 MD5 Tècnica hashing
SHA512 utilitza una funció criptogràfica que ocupa la contrasenya de text sense format de 64 bits i la converteix en un valor hash de mida fixa de 512 bits. Aquesta tècnica de hash també s'implementa mitjançant la classe MessageDiagest del paquet java.security.
cicle de vida sdlc
PassEncTech2.java
import java.math.BigInteger; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class PassEncTech2 { public static byte[] getSHA(String input) throws NoSuchAlgorithmException { /* MessageDigest instance for hashing using SHA512*/ MessageDigest md = MessageDigest.getInstance('SHA-512'); /* digest() method called to calculate message digest of an input and return array of byte */ return md.digest(input.getBytes(StandardCharsets.UTF_8)); } public static String toHexString(byte[] hash) { /* Convert byte array of hash into digest */ BigInteger number = new BigInteger(1, hash); /* Convert the digest into hex value */ StringBuilder hexString = new StringBuilder(number.toString(16)); /* Pad with leading zeros */ while (hexString.length() <32) { hexstring.insert(0, \'0\'); } return hexstring.tostring(); * driver code public static void main(string args[]) try string string1="myPassword" ; system.out.println(\'
\' + \' : tohexstring(getsha(string1))); string2="hashtrial" tohexstring(getsha(string2))); catch (nosuchalgorithmexception e) system.out.println(\'exception thrown for incorrect algorithm: e); < pre> <p> <strong>Output:</strong> </p> <pre> myPassword : 450ad03db9395dfccb5e03066fd7f16cfba2b61e23d516373714471459052ec90a9a4bf3a151e600ea8aaed36e3b8c21a3d38ab1705839749d130da4380f1448 hashtrial : 9520ea1a8d60d23334e6d59acebd587de6fec1e53db5836f467096c540ae60f7c85e9fbc90856dee9d6563609b8786b03b47892af0bad44bdcab2206f22df5cb </pre> <p>The above code uses the instance of <strong> <em>MessageDigest</em> </strong> class to generate a hash for <strong> <em>SHA512</em> </strong> . The SHA512 returns a byte array that needs to be converted into a readable hexadecimal format. And lastly, the encrypted hash value is displayed.</p> <h3>Password-Based Encryption using Salt and Base64:</h3> <p>The password-based encryption technique uses plain text passwords and salt values to generate a hash value. And the hash value is then encoded as a Base64 string. Salt value contains random data generated using an instance of Random class from java.util package.</p> <p>The following program demonstrates password encryption using salt and base64.</p> <p> <strong>PassEncTech4.java</strong> </p> <pre> import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.security.spec.InvalidKeySpecException; import java.util.Arrays; import java.util.Base64; import java.util.Random; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.PBEKeySpec; public class PassEncTech4 { /* Driver Code */ public static void main(String[] args) { /* Plain text Password. */ String password = 'myNewPass123'; /* generates the Salt value. It can be stored in a database. */ String saltvalue = PassBasedEnc.getSaltvalue(30); /* generates an encrypted password. It can be stored in a database.*/ String encryptedpassword = PassBasedEnc.generateSecurePassword(password, saltvalue); /* Print out plain text password, encrypted password and salt value. */ System.out.println('Plain text password = ' + password); System.out.println('Secure password = ' + encryptedpassword); System.out.println('Salt value = ' + saltvalue); /* verify the original password and encrypted password */ Boolean status = PassBasedEnc.verifyUserPassword(password,encryptedpassword,saltvalue); if(status==true) System.out.println('Password Matched!!'); else System.out.println('Password Mismatched'); } } class PassBasedEnc { /* Declaration of variables */ private static final Random random = new SecureRandom(); private static final String characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; private static final int iterations = 10000; private static final int keylength = 256; /* Method to generate the salt value. */ public static String getSaltvalue(int length) { StringBuilder finalval = new StringBuilder(length); for (int i = 0; i <length; i++) { finalval.append(characters.charat(random.nextint(characters.length()))); } return new string(finalval); * method to generate the hash value public static byte[] hash(char[] password, salt) pbekeyspec spec="new" pbekeyspec(password, salt, iterations, keylength); arrays.fill(password, character.min_value); try secretkeyfactory skf="SecretKeyFactory.getInstance('PBKDF2WithHmacSHA1');" skf.generatesecret(spec).getencoded(); catch (nosuchalgorithmexception | invalidkeyspecexception e) throw assertionerror(\'error while hashing a password: \' + e.getmessage(), e); finally spec.clearpassword(); encrypt password using original and salt value. string generatesecurepassword(string finalval="null;" securepassword="hash(password.toCharArray()," salt.getbytes()); finalval; verify if both matches or not boolean verifyuserpassword(string providedpassword, securedpassword, secure with same newsecurepassword="generateSecurePassword(providedPassword," salt); check two passwords are equal < pre> <p> <strong>Output:</strong> </p> <pre> Plain text password = myNewPass123 Secure password = sA0jNGQTrAfMUiqrB++bMKTU55ThdFCl16ZZTIXwD2M= Salt value = n7d9MPQFXxDqzT6onmong3hQt8Nyko Password Matched!! </pre> <p>In the above code, two classes are defined.</p> <ol class="points"> <li>The class <strong> <em>PassEncTech4</em> </strong> contains the driver code for the program. It generates a salt value and encrypted password using the given plain-text password. And verifies them using the value returned by the <strong> <em>verifyUserPassword() </em> </strong> </li> <li>In the class <strong> <em>PassBasedEnc, </em> </strong> 4 methods are defined. The first method is <strong> <em>getSaltvalue()</em> </strong> which generates the value using <strong> <em>Random</em> </strong> class from <strong> <em>util</em> </strong> package. Then <strong> <em>hash()</em> </strong> is defined that has a return type of byte array. The <strong> <em>generateSecurePassword() </em> </strong> uses plain-text password and salt value with the <strong> <em>hash()</em> </strong> method. And lastly, the two passwords are matched using the <strong> <em>verifyUserPassword()</em> </strong> method.</li> </ol> <h2>Techniques for Cracking the Hash</h2> <p>A hash value is prone to different kinds of attacks by attackers. Some of them are mentioned below,</p> <ol class="points"> <tr><td>Brute force attack:</td> In the brute force attack, the attacker submits multiple combinations of passphrases or passwords in the hope that one of the combinations will match and he can enter into the system. <br> To avoid this kind of attack the passphrase should use a combination of alphabets, numbers and symbols. Another way is to set a fixed number of invalid attempts and after that ask for human verification like a captcha. </tr><tr><td>Dictionary attack:</td> Dictionary attack is an enhanced version of brute force attack. In this technique, the encrypted cipher is tried to be decrypted using multiple possibilities, like the words in a dictionary. </tr><tr><td>Rainbow tables:</td> The technique is about a rainbow table that is precomputed table for reversing the cryptographic hash functions. The rainbow tables are used to discover the plain text passwords up to a certain length and a limited number of characters. So it uses a side-loop table in order to reduce the storage usage and increase the speed of attack. </tr></ol> <hr></length;></pre></32)> El codi anterior utilitza la instància de Resum de missatges classe per generar un hash SHA512 . El SHA512 retorna una matriu de bytes que s'ha de convertir en un format hexadecimal llegible. I, finalment, es mostra el valor hash xifrat.
Xifratge basat en contrasenya amb Salt i Base64:
La tècnica de xifratge basada en contrasenyes utilitza contrasenyes de text sense format i valors de sal per generar un valor hash. I el valor hash es codifica com a cadena Base64. El valor de sal conté dades aleatòries generades mitjançant una instància de la classe Random del paquet java.util.
El programa següent mostra el xifratge de contrasenyes amb salt i base64.
PassEncTech4.java
import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.security.spec.InvalidKeySpecException; import java.util.Arrays; import java.util.Base64; import java.util.Random; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.PBEKeySpec; public class PassEncTech4 { /* Driver Code */ public static void main(String[] args) { /* Plain text Password. */ String password = 'myNewPass123'; /* generates the Salt value. It can be stored in a database. */ String saltvalue = PassBasedEnc.getSaltvalue(30); /* generates an encrypted password. It can be stored in a database.*/ String encryptedpassword = PassBasedEnc.generateSecurePassword(password, saltvalue); /* Print out plain text password, encrypted password and salt value. */ System.out.println('Plain text password = ' + password); System.out.println('Secure password = ' + encryptedpassword); System.out.println('Salt value = ' + saltvalue); /* verify the original password and encrypted password */ Boolean status = PassBasedEnc.verifyUserPassword(password,encryptedpassword,saltvalue); if(status==true) System.out.println('Password Matched!!'); else System.out.println('Password Mismatched'); } } class PassBasedEnc { /* Declaration of variables */ private static final Random random = new SecureRandom(); private static final String characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; private static final int iterations = 10000; private static final int keylength = 256; /* Method to generate the salt value. */ public static String getSaltvalue(int length) { StringBuilder finalval = new StringBuilder(length); for (int i = 0; i <length; i++) { finalval.append(characters.charat(random.nextint(characters.length()))); } return new string(finalval); * method to generate the hash value public static byte[] hash(char[] password, salt) pbekeyspec spec="new" pbekeyspec(password, salt, iterations, keylength); arrays.fill(password, character.min_value); try secretkeyfactory skf="SecretKeyFactory.getInstance('PBKDF2WithHmacSHA1');" skf.generatesecret(spec).getencoded(); catch (nosuchalgorithmexception | invalidkeyspecexception e) throw assertionerror(\'error while hashing a password: \' + e.getmessage(), e); finally spec.clearpassword(); encrypt password using original and salt value. string generatesecurepassword(string finalval="null;" securepassword="hash(password.toCharArray()," salt.getbytes()); finalval; verify if both matches or not boolean verifyuserpassword(string providedpassword, securedpassword, secure with same newsecurepassword="generateSecurePassword(providedPassword," salt); check two passwords are equal < pre> <p> <strong>Output:</strong> </p> <pre> Plain text password = myNewPass123 Secure password = sA0jNGQTrAfMUiqrB++bMKTU55ThdFCl16ZZTIXwD2M= Salt value = n7d9MPQFXxDqzT6onmong3hQt8Nyko Password Matched!! </pre> <p>In the above code, two classes are defined.</p> <ol class="points"> <li>The class <strong> <em>PassEncTech4</em> </strong> contains the driver code for the program. It generates a salt value and encrypted password using the given plain-text password. And verifies them using the value returned by the <strong> <em>verifyUserPassword() </em> </strong> </li> <li>In the class <strong> <em>PassBasedEnc, </em> </strong> 4 methods are defined. The first method is <strong> <em>getSaltvalue()</em> </strong> which generates the value using <strong> <em>Random</em> </strong> class from <strong> <em>util</em> </strong> package. Then <strong> <em>hash()</em> </strong> is defined that has a return type of byte array. The <strong> <em>generateSecurePassword() </em> </strong> uses plain-text password and salt value with the <strong> <em>hash()</em> </strong> method. And lastly, the two passwords are matched using the <strong> <em>verifyUserPassword()</em> </strong> method.</li> </ol> <h2>Techniques for Cracking the Hash</h2> <p>A hash value is prone to different kinds of attacks by attackers. Some of them are mentioned below,</p> <ol class="points"> <tr><td>Brute force attack:</td> In the brute force attack, the attacker submits multiple combinations of passphrases or passwords in the hope that one of the combinations will match and he can enter into the system. <br> To avoid this kind of attack the passphrase should use a combination of alphabets, numbers and symbols. Another way is to set a fixed number of invalid attempts and after that ask for human verification like a captcha. </tr><tr><td>Dictionary attack:</td> Dictionary attack is an enhanced version of brute force attack. In this technique, the encrypted cipher is tried to be decrypted using multiple possibilities, like the words in a dictionary. </tr><tr><td>Rainbow tables:</td> The technique is about a rainbow table that is precomputed table for reversing the cryptographic hash functions. The rainbow tables are used to discover the plain text passwords up to a certain length and a limited number of characters. So it uses a side-loop table in order to reduce the storage usage and increase the speed of attack. </tr></ol> <hr></length;> En el codi anterior, es defineixen dues classes.
- La classe PassEncTech4 conté el codi del controlador del programa. Genera un valor de sal i una contrasenya xifrada utilitzant la contrasenya de text pla donada. I els verifica utilitzant el valor que retorna verificar la contrasenya d'usuari()
- A la classe PassBasedEnc, Es defineixen 4 mètodes. El primer mètode és getSaltvalue() que genera el valor utilitzant aleatòria classe des de útil paquet. Aleshores hash () es defineix que té un tipus de retorn de matriu de bytes. El generateSecurePassword() utilitza una contrasenya de text sense format i un valor de sal amb el hash () mètode. I, per últim, les dues contrasenyes coincideixen amb el verificar la contrasenya d'usuari() mètode.
Tècniques per trencar el hash
Un valor hash és propens a diferents tipus d'atacs per part dels atacants. Alguns d'ells s'esmenten a continuació,
Per evitar aquest tipus d'atac, la frase de contrasenya hauria d'utilitzar una combinació d'alfabets, números i símbols. Una altra manera és establir un nombre fix d'intents no vàlids i després demanar una verificació humana com un captcha.