我正在编写一些代码来模拟比特币网络完成的工作量证明，当我突然变得好奇时生成块：你如何创建一个包含它自己的哈希值的数据？
为了好玩，我编写了一个程序，试图创建包含它自己的哈希值的数据。生成4个随机字节，然后在末尾添加随机数，并用CRC32对整个值进行散列。随机数增加，并且该过程重复，直到程序找到与原始4字节匹配的散列。 注意：随机数可以无限增加。
以下是大约1,980,000,000次尝试后的输出示例：
Found a match!
Data: 7a73a2d4ab833876
Original hash: 7a73a2d4 new hash: 7a73a2d4
这有可能吗？
package selfhash;
import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
/**
*
* @author dylan
*/
public class SelfHash {
static byte[] data;
static byte[] hash = new byte[4];
public static void main(String[] args) {
// TODO code application logic here
SecureRandom random = new SecureRandom();
random.nextBytes(hash);
data = new byte[hash.length + 1];
System.arraycopy(hash, 0, data, 0, hash.length);
long c = 0;
while (true) {
recalculateData();
byte[] dataHash = crc32AsByteArray(data);
if (c % 10000000 == 0) {
System.out.println("Calculated " + c + " hashes");
System.out.println("Data: " + byteArrayToHex(data));
System.out.println("Original hash: " + byteArrayToHex(hash) + " new hash: " + byteArrayToHex(dataHash));
}
if (Arrays.equals(hash, dataHash)) {
System.out.println("Found a match!");
System.out.println("Data: " + byteArrayToHex(data));
System.out.println("Original hash: " + byteArrayToHex(hash) + " new hash: " + byteArrayToHex(dataHash));
break;
}
c++;
}
}
public static void recalculateData() {
int position = hash.length;
while (true) {
int valueAtPosition = unsignedToBytes(data[position]);
if (valueAtPosition == 255) {
//increase size of data
if (position == data.length-1) {
byte[] newData = new byte[data.length + 1];
System.arraycopy(data, 0, newData, 0, data.length);
data = newData;
}
data[position] = (byte) (0);
position++;
} else {
data[position] = (byte) (valueAtPosition + 1);
break;
}
}
}
public static byte[] hexToByteArray(String hexString) {
int len = hexString.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
data[i / 2] = (byte) ((Character.digit(hexString.charAt(i), 16) << 4)
+ Character.digit(hexString.charAt(i + 1), 16));
}
return data;
}
private static final char[] BYTE2HEX = ("000102030405060708090A0B0C0D0E0F"
+ "101112131415161718191A1B1C1D1E1F"
+ "202122232425262728292A2B2C2D2E2F"
+ "303132333435363738393A3B3C3D3E3F"
+ "404142434445464748494A4B4C4D4E4F"
+ "505152535455565758595A5B5C5D5E5F"
+ "606162636465666768696A6B6C6D6E6F"
+ "707172737475767778797A7B7C7D7E7F"
+ "808182838485868788898A8B8C8D8E8F"
+ "909192939495969798999A9B9C9D9E9F"
+ "A0A1A2A3A4A5A6A7A8A9AAABACADAEAF"
+ "B0B1B2B3B4B5B6B7B8B9BABBBCBDBEBF"
+ "C0C1C2C3C4C5C6C7C8C9CACBCCCDCECF"
+ "D0D1D2D3D4D5D6D7D8D9DADBDCDDDEDF"
+ "E0E1E2E3E4E5E6E7E8E9EAEBECEDEEEF"
+ "F0F1F2F3F4F5F6F7F8F9FAFBFCFDFEFF").toLowerCase().toCharArray();
;
public static String byteArrayToHex(byte[] bytes) {
final int len = bytes.length;
final char[] chars = new char[len << 1];
int hexIndex;
int idx = 0;
int ofs = 0;
while (ofs < len) {
hexIndex = (bytes[ofs++] & 0xFF) << 1;
chars[idx++] = BYTE2HEX[hexIndex++];
chars[idx++] = BYTE2HEX[hexIndex];
}
return new String(chars);
}
public static String sha256AsHexString(byte[] bytes) {
try {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
return byteArrayToHex(digest.digest(bytes));
} catch (Exception e) {
throw new Error(e);
}
}
public static byte[] sha256AsByteArray(byte[] bytes) {
try {
MessageDigest digest = MessageDigest.getInstance("SHA-256");
return digest.digest(bytes);
} catch (Exception e) {
throw new Error(e);
}
}
public static byte[] crc32AsByteArray(byte[] bytes) {
Checksum checksum = new CRC32();
checksum.update(bytes, 0, bytes.length);
long value = checksum.getValue();
byte[] resultExcess = ByteBuffer.allocate(8).putLong(value).array();
byte[] result = new byte[4];
System.arraycopy(resultExcess, 4, result, 0, 4);
return result;
}
public static int unsignedToBytes(byte b) {
return b & 0xFF;
}
}