Katrai lietojumprogrammai ir nepieciešams lietotājvārds un parole, lai autentificētu derīgo lietotāju. Lietotājvārds var būt jebkas, piemēram, e-pasta ID vai tikai rakstzīmju kombinācija. Bet, veidojot paroli, jābūt ļoti uzmanīgiem. Tā kā ikviens, kam ir derīgi akreditācijas dati, var iekļūt sistēmā un piekļūt informācijai.
metodes pārslodze
Nepieciešamība šifrēt paroli
Kad lietotājs iestata savu paroli, tā tiek saglabāta datu bāzē kā vienkāršs teksts. Vienkāršā teksta glabāšana datu bāzē vispār nav droša. Hakeri var uzlauzt sistēmu un nozagt paroles no datu bāzes.
Lai nodrošinātu lietotāja paroles drošību, tā tiek šifrēta, izmantojot dažādas šifrēšanas metodes. Izmantojot dažādas šifrēšanas metodes, vienkāršā teksta parole tiek saglabāta šifrētā veidā datu bāzē. Paroles šifrēšanai var izmantot daudzas metodes. Bet jaukšana ir viena no populārākajām šifrēšanas metodēm.
Java drošās jaukšanas metodes
Šifrētā jaucējvērtība tiek ģenerēta, izmantojot noteiktus algoritmus, izmantojot lietotāja nodrošināto vienkārša teksta paroli. Java programmēšana atbalsta vairākas jaukšanas metodes, lai šifrētu paroli.
MD5 jaukšanas tehnika
MD5 (Message Digest) ir ļoti populārs jaukšanas algoritms. Tā ir kriptogrāfiska jaucējfunkcija, kas ģenerē 128 bitu jaucējvērtību. Šis algoritms ir definēts Java programmēšanas pakotnē java.security.
PassEncTech1.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> Iepriekš minētais kods parāda ieviešanu Message Digest klasē iekšā java.security iepakojums. MD5 atgriež baitu masīvu, kas ir jāpārvērš lasāmā heksadecimālā formātā.
MD5 jaukšanas paņēmiens ir viegli un ātri ieviešams, taču tas ir arī pakļauts brutāla spēka uzbrukumiem vai vārdnīcu uzbrukumiem.
galvenie java intervijas jautājumi
SHA256
SHA ir Secure Hash algoritms. Tas izmanto kriptogrāfijas funkciju, kas aizņem 32 bitu vienkāršā teksta paroli un pārvērš to fiksēta izmēra 256 bitu jaucējvērtībā. Šī jaukšanas metode ir ieviesta, izmantojot java.security pakotnes MessageDiagest klasi.
Tā ir vienvirziena šifrēšanas tehnika. Kad ieejas frāze ir šifrēta, to vairs nevar atšifrēt.
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)> Iepriekš minētais kods izmanto gadījumu Message Digest klasē, lai ģenerētu jaucējkodu SHA256 . SHA256 atgriež baitu masīvu, kas ir jāpārvērš lasāmā heksadecimālā formātā. Un visbeidzot, tiek parādīta šifrētā hash vērtība.
SHA512 MD5 jaukšanas tehnika
SHA512 izmanto kriptogrāfijas funkciju, kas aizņem 64 bitu vienkārša teksta paroli un pārvērš to fiksēta izmēra 512 bitu jaucējvērtībā. Šī jaukšanas tehnika tiek ieviesta arī, izmantojot java.security pakotnes MessageDiagest klasi.
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)> Iepriekš minētais kods izmanto gadījumu Message Digest klasē, lai ģenerētu jaucējkodu SHA512 . SHA512 atgriež baitu masīvu, kas ir jāpārvērš lasāmā heksadecimālā formātā. Un visbeidzot, tiek parādīta šifrētā hash vērtība.
virkne c
Uz paroli balstīta šifrēšana, izmantojot Salt un Base64:
Uz paroli balstītā šifrēšanas tehnika izmanto vienkārša teksta paroles un sāls vērtības, lai ģenerētu jaucējvērtību. Pēc tam jaucējvērtība tiek kodēta kā Base64 virkne. Sāls vērtība satur nejaušus datus, kas ģenerēti, izmantojot java.util pakotnes Random klases gadījumu.
Šī programma demonstrē paroles šifrēšanu, izmantojot sāls un 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;> Iepriekš minētajā kodā ir definētas divas klases.
- Klase PassEncTech4 satur programmas draivera kodu. Tas ģenerē sāls vērtību un šifrētu paroli, izmantojot doto vienkāršā teksta paroli. Un pārbauda tos, izmantojot vērtību, ko atgriež verifyUserPassword()
- Klasē PassBasedEnc, Ir definētas 4 metodes. Pirmā metode ir getSaltvalue() kas ģenerē vērtību, izmantojot nejauši klase no util iepakojums. Tad hash () ir definēts, kam ir baitu masīva atgriešanas veids. The generētSecurePassword() izmanto vienkārša teksta paroli un sāls vērtību ar hash () metodi. Visbeidzot, abas paroles tiek saskaņotas, izmantojot verifyUserPassword() metodi.
Haša uzlaušanas paņēmieni
Jaucējvērtība ir pakļauta dažāda veida uzbrucēju uzbrukumiem. Daži no tiem ir minēti tālāk,
Lai izvairītos no šāda veida uzbrukumiem, ieejas frāzē jāizmanto alfabētu, ciparu un simbolu kombinācija. Vēl viens veids ir iestatīt fiksētu nederīgu mēģinājumu skaitu un pēc tam lūgt cilvēka verifikāciju, piemēram, captcha.