可能重复：
是否可以解密 md5 哈希？
是否可以从 Java 中的 MD5 获取字符串？
首先将一个字符串转换为 MD5 校验和，是否可以将此 MD5 校验和恢复为原始文本？
我假设您使用 MessageDigest，非常感谢任何帮助，甚至是其他 java 库。
还想指出这个应用程序是否不可能：https ://play.google.com/store/apps/details?id=com.fab.md5&hl=en
我什至使用另一个应用程序将一些文本转换为 MD5 校验和，并使用此校验和来查看应用程序是否能够将其转换回文本并且确实如此。
不，那是不可能的，因为
MD5 及其散列函数家族的目标是
认为你可以得到任何字符串的 MD5，甚至很长。并且 MD5 只有 16 个字节长（如果你用 hexa 编写它以更容易地存储或分发它，则为 32 个字节）。如果你能扭转它们，你就会有一个神奇的压缩方案。
话虽这么说，由于世界上使用的短字符串（密码......）并不多，您可以从字典（称为“暴力攻击”）甚至谷歌搜索您的 MD5 来测试它们。如果这个词很常见并且没有加盐，那么您就有合理的机会成功...
这不可能是散列的全部意义所在。但是，您可以通过所有可能性（以每个可能的顺序使用所有可能的数字字符）并对它们进行散列并检查冲突来进行暴力破解。
有关散列和 MD5 等的更多信息，请参见：http ://en.wikipedia.org/wiki/MD5、http : //en.wikipedia.org/wiki/Hash_function、http : //en.wikipedia.org/wiki/ Cryptographic_hash_function和http://onin.com/hhh/hhhexpl.html
我自己创建了自己的应用程序来执行此操作，它的开源您可以查看链接： http: //sourceforge.net/projects/jpassrecovery/，当然还有源代码。这是易于访问的源代码，它在评论中有一个基本的实现：
Bruter.java：
import java.util.ArrayList;
public class Bruter {
public ArrayList<String> characters = new ArrayList<>();
public boolean found = false;
public int maxLength;
public int minLength;
public int count;
long starttime, endtime;
public int minutes, seconds, hours, days;
public char[] specialCharacters = {'~', '`', '!', '@', '#', '$', '%', '^',
'&', '*', '(', ')', '_', '-', '+', '=', '{', '}', '[', ']', '|', '\\',
';', ':', '\'', '"', '<', '.', ',', '>', '/', '?', ' '};
public boolean done = false;
public boolean paused = false;
public boolean isFound() {
return found;
}
public void setPaused(boolean paused) {
this.paused = paused;
}
public boolean isPaused() {
return paused;
}
public void setFound(boolean found) {
this.found = found;
}
public synchronized void setEndtime(long endtime) {
this.endtime = endtime;
}
public int getCounter() {
return count;
}
public long getRemainder() {
return getNumberOfPossibilities() - count;
}
public long getNumberOfPossibilities() {
long possibilities = 0;
for (int i = minLength; i <= maxLength; i++) {
possibilities += (long) Math.pow(characters.size(), i);
}
return possibilities;
}
public void addExtendedSet() {
for (char c = (char) 0; c <= (char) 31; c++) {
characters.add(String.valueOf(c));
}
}
public void addStandardCharacterSet() {
for (char c = (char) 32; c <= (char) 127; c++) {
characters.add(String.valueOf(c));
}
}
public void addLowerCaseLetters() {
for (char c = 'a'; c <= 'z'; c++) {
characters.add(String.valueOf(c));
}
}
public void addDigits() {
for (int c = 0; c <= 9; c++) {
characters.add(String.valueOf(c));
}
}
public void addUpperCaseLetters() {
for (char c = 'A'; c <= 'Z'; c++) {
characters.add(String.valueOf(c));
}
}
public void addSpecialCharacters() {
for (char c : specialCharacters) {
characters.add(String.valueOf(c));
}
}
public void setMaxLength(int i) {
maxLength = i;
}
public void setMinLength(int i) {
minLength = i;
}
public int getPerSecond() {
int i;
try {
i = (int) (getCounter() / calculateTimeDifference());
} catch (Exception ex) {
return 0;
}
return i;
}
public String calculateTimeElapsed() {
long timeTaken = calculateTimeDifference();
seconds = (int) timeTaken;
if (seconds > 60) {
minutes = (int) (seconds / 60);
if (minutes * 60 > seconds) {
minutes = minutes - 1;
}
if (minutes > 60) {
hours = (int) minutes / 60;
if (hours * 60 > minutes) {
hours = hours - 1;
}
}
if (hours > 24) {
days = (int) hours / 24;
if (days * 24 > hours) {
days = days - 1;
}
}
seconds -= (minutes * 60);
minutes -= (hours * 60);
hours -= (days * 24);
days -= (hours * 24);
}
return "Time elapsed: " + days + "days " + hours + "h " + minutes + "min " + seconds + "s";
}
private long calculateTimeDifference() {
long timeTaken = (long) ((endtime - starttime) * (1 * Math.pow(10, -9)));
return timeTaken;
}
public boolean excludeChars(String s) {
char[] arrayChars = s.toCharArray();
for (int i = 0; i < arrayChars.length; i++) {
characters.remove(arrayChars[i] + "");
}
if (characters.size() < maxLength) {
return false;
} else {
return true;
}
}
public int getMaxLength() {
return maxLength;
}
public int getMinLength() {
return minLength;
}
public void setIsDone(Boolean b) {
done = b;
}
public boolean isDone() {
return done;
}
}
HashBruter.java：
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.Adler32;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
import javax.swing.JOptionPane;
public class HashBruter extends Bruter {
/*
* public static void main(String[] args) {
*
* final HashBruter hb = new HashBruter();
*
* hb.setMaxLength(5); hb.setMinLength(1);
*
* hb.addSpecialCharacters(); hb.addUpperCaseLetters();
* hb.addLowerCaseLetters(); hb.addDigits();
*
* hb.setType("sha-512");
*
* hb.setHash("282154720ABD4FA76AD7CD5F8806AA8A19AEFB6D10042B0D57A311B86087DE4DE3186A92019D6EE51035106EE088DC6007BEB7BE46994D1463999968FBE9760E");
*
* Thread thread = new Thread(new Runnable() {
*
* @Override public void run() { hb.tryBruteForce(); } });
*
* thread.start();
*
* while (!hb.isFound()) { System.out.println("Hash: " +
* hb.getGeneratedHash()); System.out.println("Number of Possibilities: " +
* hb.getNumberOfPossibilities()); System.out.println("Checked hashes: " +
* hb.getCounter()); System.out.println("Estimated hashes left: " +
* hb.getRemainder()); }
*
* System.out.println("Found " + hb.getType() + " hash collision: " +
* hb.getGeneratedHash() + " password is: " + hb.getPassword());
*
* }
*/
public String hash, generatedHash, password;
public String type;
public String getType() {
return type;
}
public String getPassword() {
return password;
}
public void setHash(String p) {
hash = p;
}
public void setType(String digestType) {
type = digestType;
}
public String getGeneratedHash() {
return generatedHash;
}
public void tryBruteForce() {
starttime = System.nanoTime();
for (int size = minLength; size <= maxLength; size++) {
if (found == true || done == true) {
break;
} else {
while (paused) {
try {
Thread.sleep(500);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
}
generateAllPossibleCombinations("", size);
}
}
done = true;
}
private void generateAllPossibleCombinations(String baseString, int length) {
while (paused) {
try {
Thread.sleep(500);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
}
if (found == false || done == false) {
if (baseString.length() == length) {
if(type.equalsIgnoreCase("crc32")) {
generatedHash = generateCRC32(baseString);
} else if(type.equalsIgnoreCase("adler32")) {
generatedHash = generateAdler32(baseString);
} else if(type.equalsIgnoreCase("crc16")) {
generatedHash=generateCRC16(baseString);
} else if(type.equalsIgnoreCase("crc64")) {
generatedHash=generateCRC64(baseString.getBytes());
}
else {
generatedHash = generateHash(baseString.toCharArray());
}
password = baseString;
if (hash.equals(generatedHash)) {
password = baseString;
found = true;
done = true;
}
count++;
} else if (baseString.length() < length) {
for (int n = 0; n < characters.size(); n++) {
generateAllPossibleCombinations(baseString + characters.get(n), length);
}
}
}
}
private String generateHash(char[] passwordChar) {
MessageDigest md = null;
try {
md = MessageDigest.getInstance(type);
} catch (NoSuchAlgorithmException e1) {
JOptionPane.showMessageDialog(null, "No such algorithm for hashes exists", "Error", JOptionPane.ERROR_MESSAGE);
}
String passwordString = new String(passwordChar);
byte[] passwordByte = passwordString.getBytes();
md.update(passwordByte, 0, passwordByte.length);
byte[] encodedPassword = md.digest();
String encodedPasswordInString = toHexString(encodedPassword);
return encodedPasswordInString;
}
private void byte2hex(byte b, StringBuffer buf) {
char[] hexChars = {'0', '1', '2', '3', '4', '5', '6', '7', '8',
'9', 'A', 'B', 'C', 'D', 'E', 'F'};
int high = ((b & 0xf0) >> 4);
int low = (b & 0x0f);
buf.append(hexChars[high]);
buf.append(hexChars[low]);
}
private String toHexString(byte[] block) {
StringBuffer buf = new StringBuffer();
int len = block.length;
for (int i = 0; i < len; i++) {
byte2hex(block[i], buf);
}
return buf.toString();
}
private String generateCRC32(String baseString) {
//Convert string to bytes
byte bytes[] = baseString.getBytes();
Checksum checksum = new CRC32();
/*
* To compute the CRC32 checksum for byte array, use
*
* void update(bytes[] b, int start, int length)
* method of CRC32 class.
*/
checksum.update(bytes,0,bytes.length);
/*
* Get the generated checksum using
* getValue method of CRC32 class.
*/
return String.valueOf(checksum.getValue());
}
private String generateAdler32(String baseString) {
//Convert string to bytes
byte bytes[] = baseString.getBytes();
Checksum checksum = new Adler32();
/*
* To compute the CRC32 checksum for byte array, use
*
* void update(bytes[] b, int start, int length)
* method of CRC32 class.
*/
checksum.update(bytes,0,bytes.length);
/*
* Get the generated checksum using
* getValue method of CRC32 class.
*/
return String.valueOf(checksum.getValue());
}
/*************************************************************************
* Compilation: javac CRC16.java
* Execution: java CRC16 s
*
* Reads in a string s as a command-line argument, and prints out
* its 16-bit Cyclic Redundancy Check (CRC16). Uses a lookup table.
*
* Reference: http://www.gelato.unsw.edu.au/lxr/source/lib/crc16.c
*
* % java CRC16 123456789
* CRC16 = bb3d
*
* Uses irreducible polynomial: 1 + x^2 + x^15 + x^16
*
*
*************************************************************************/
private String generateCRC16(String baseString) {
int[] table = {
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040,
};
byte[] bytes = baseString.getBytes();
int crc = 0x0000;
for (byte b : bytes) {
crc = (crc >>> 8) ^ table[(crc ^ b) & 0xff];
}
return Integer.toHexString(crc);
}
/*******************************************************************************
* Copyright (c) 2009, 2012 Mountainminds GmbH & Co. KG and Contributors
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Marc R. Hoffmann - initial API and implementation
*
*******************************************************************************/
/**
* CRC64 checksum calculator based on the polynom specified in ISO 3309. The
* implementation is based on the following publications:
*
* <ul>
* <li>http://en.wikipedia.org/wiki/Cyclic_redundancy_check</li>
* <li>http://www.geocities.com/SiliconValley/Pines/8659/crc.htm</li>
* </ul>
*/
private static final long POLY64REV = 0xd800000000000000L;
private static final long[] LOOKUPTABLE;
static {
LOOKUPTABLE = new long[0x100];
for (int i = 0; i < 0x100; i++) {
long v = i;
for (int j = 0; j < 8; j++) {
if ((v & 1) == 1) {
v = (v >>> 1) ^ POLY64REV;
} else {
v = (v >>> 1);
}
}
LOOKUPTABLE[i] = v;
}
}
/**
* Calculates the CRC64 checksum for the given data array.
*
* @param data
* data to calculate checksum for
* @return checksum value
*/
public static String generateCRC64(final byte[] data) {
long sum = 0;
for (int i = 0; i < data.length; i++) {
final int lookupidx = ((int) sum ^ data[i]) & 0xff;
sum = (sum >>> 8) ^ LOOKUPTABLE[lookupidx];
}
return String.valueOf(sum);
}
}
你会像这样使用它：
final HashBruter hb = new HashBruter();
hb.setMaxLength(5); hb.setMinLength(1);
hb.addSpecialCharacters(); hb.addUpperCaseLetters();
hb.addLowerCaseLetters(); hb.addDigits();
hb.setType("sha-512");
hb.setHash("282154720ABD4FA76AD7CD5F8806AA8A19AEFB6D10042B0D57A311B86087DE4DE3186A92019D6EE51035106EE088DC6007BEB7BE46994D1463999968FBE9760E");
Thread thread = new Thread(new Runnable() {
@Override public void run() { hb.tryBruteForce(); } });
thread.start();
while (!hb.isFound()) { System.out.println("Hash: " +
hb.getGeneratedHash()); System.out.println("Number of Possibilities: " +
hb.getNumberOfPossibilities()); System.out.println("Checked hashes: " +
hb.getCounter()); System.out.println("Estimated hashes left: " +
hb.getRemainder()); }
System.out.println("Found " + hb.getType() + " hash collision: " +
hb.getGeneratedHash() + " password is: " + hb.getPassword());