我正在嘗試用 Java 編寫一個非常簡單的 merkle-tree 實現。我使用比特幣區塊鏈上第170 個區塊中的 txid 值作為參考，所以我可以看到正確的結果應該是什么。該區塊對應的txid如下：b1fea52486ce0c62bb442b530a3f0132b826c74e473d1f2c220bfa78111c5082f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16據我了解，比特幣的 merkle-tree 實現方式如下：將區塊中的交易拆分成對字節交換 txid連接 txid對連接的對進行雙重哈希需要注意的是：If there's no additional pairs of txids, concatenate the result of the first pair after double hashing with itself and repeat我寫的 swapEndianness 方法不是真正的“字節級”交換，而只是改變了字符串的順序，它看起來像這樣：public static String swapEndianness(String hash) { char[] hashAsCharArray = hash.toCharArray(); StringBuilder sb = new StringBuilder(); for (int i = hash.length() - 1; i > 0; i-=2) { sb.append(hashAsCharArray[i - 1]); sb.append(hashAsCharArray[i]); } return sb.toString(); }這兩個 txid 的默克爾根的預期結果是：7dac2c5666815c17a3b36427de37bb9d2e2c5ccec3f8633eb91a4205cb4c10ff然而，我最終得到的結果是：3b40cab1157838cc41b08e27641f65d245957ab07b3504d94bc2d355abaed06c我沒有得到我期望的結果是因為我在進行字節交換時作弊，因為我錯過了一個步驟，還是因為我的代碼有錯誤（或這些錯誤的某種組合）？任何幫助，將不勝感激！
1 回答
慕容3067478
TA貢獻1773條經驗 獲得超3個贊
您不了解 Java 中的 byte[] 是什么。您示例中的字符串是 byte[] 的“十六進制”表示形式。請參閱如何在 Java 中初始化字節數組？
public class MerkleTree {
static MessageDigest digest;
public static void main(String[] args) throws NoSuchAlgorithmException {
digest = MessageDigest.getInstance("SHA-256");
new MerkleTree().run();
}
private void run() {
// txid A
byte[] A = hexStringToByteArray("b1fea52486ce0c62bb442b530a3f0132b826c74e473d1f2c220bfa78111c5082");
System.out.println(Arrays.toString(A));
// txid A byte-swapped
byte[] A_little = swapEndianness(A);
System.out.println(Arrays.toString(A_little));
// txid B
byte[] B = hexStringToByteArray("f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16");
System.out.println(Arrays.toString(B));
// txid B byte-swapped
byte[] B_little = swapEndianness(B);
System.out.println(Arrays.toString(B_little));
// txid A + B concatenated
byte[] AB_little = Arrays.copyOf(A_little, A_little.length + B_little.length);
System.arraycopy(B_little, 0, AB_little, A_little.length, B_little.length);
System.out.println(Arrays.toString(AB_little));
// double hash of byte-swapped concatenated A+B
byte[] ABdoubleHash = SHA256(SHA256(AB_little));
System.out.println(Arrays.toString(ABdoubleHash));
// print result byte-swapped back to big-endian
byte[] result = swapEndianness(ABdoubleHash);
System.out.println(Arrays.toString(result));
System.out.println(getHex(result));
}
byte[] swapEndianness(byte[] hash) {
byte[] result = new byte[hash.length];
for (int i = 0; i < hash.length; i++) {
result[i] = hash[hash.length-i-1];
}
return result;
}
byte[] SHA256(byte[] obytes) {
return digest.digest(obytes);
}
byte[] hexStringToByteArray(String s) {
int len = s.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+ Character.digit(s.charAt(i+1), 16));
}
return data;
}
private static final String HEXES = "0123456789abcdef";
String getHex(byte[] raw) {
final StringBuilder hex = new StringBuilder(2 * raw.length);
for (final byte b : raw) {
hex.append(HEXES.charAt((b & 0xF0) >> 4)).append(HEXES.charAt((b & 0x0F)));
}
return hex.toString();
}
}
最后參考Java代碼將byte轉Hexadecimal
編輯：這在資源上會好一些，因為您經常想做很多這類事情。
// txid A byte-swapped
byte[] A = swapEndianness(
hexStringToByteArray("b1fea52486ce0c62bb442b530a3f0132b826c74e473d1f2c220bfa78111c5082")
);
// txid B byte-swapped
byte[] B = swapEndianness(
hexStringToByteArray("f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16")
);
// txid A + B concatenated
byte[] AB = Arrays.copyOf(A, A.length + B.length);
System.arraycopy(B, 0, AB, A.length, B.length);
// print result byte-swapped back to big-endian
String result = getHex(swapEndianness(SHA256(SHA256(AB))));
System.out.println(result);
}
byte[] swapEndianness(byte[] hash) {
for (int i = 0; i < hash.length/2; i++) {
byte t = hash[hash.length-i-1];
hash[hash.length-i-1] = hash[i];
hash[i] = t;
}
return hash;
}
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