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June 8, 2014 14:58
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Base58 编码
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/** | |
* Copyright 2011 Google Inc. | |
* | |
* Licensed under the Apache License, Version 2.0 (the "License"); | |
* you may not use this file except in compliance with the License. | |
* You may obtain a copy of the License at | |
* | |
* http://www.apache.org/licenses/LICENSE-2.0 | |
* | |
* Unless required by applicable law or agreed to in writing, software | |
* distributed under the License is distributed on an "AS IS" BASIS, | |
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
* See the License for the specific language governing permissions and | |
* limitations under the License. | |
*/ | |
package com.google.bitcoin.core; | |
import java.io.UnsupportedEncodingException; | |
import java.math.BigInteger; | |
import java.util.Arrays; | |
/** | |
* <p>Base58 is a way to encode Bitcoin addresses as numbers and letters. Note that this is not the same base58 as used by | |
* Flickr, which you may see reference to around the internet.</p> | |
* | |
* <p>You may instead wish to work with {@link VersionedChecksummedBytes}, which adds support for testing the prefix | |
* and suffix bytes commonly found in addresses.</p> | |
* | |
* <p>Satoshi says: why base-58 instead of standard base-64 encoding?<p> | |
* | |
* <ul> | |
* <li>Don't want 0OIl characters that look the same in some fonts and | |
* could be used to create visually identical looking account numbers.</li> | |
* <li>A string with non-alphanumeric characters is not as easily accepted as an account number.</li> | |
* <li>E-mail usually won't line-break if there's no punctuation to break at.</li> | |
* <li>Doubleclicking selects the whole number as one word if it's all alphanumeric.</li> | |
* </ul> | |
*/ | |
public class Base58 { | |
public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray(); | |
private static final int[] INDEXES = new int[128]; | |
static { | |
for (int i = 0; i < INDEXES.length; i++) { | |
INDEXES[i] = -1; | |
} | |
for (int i = 0; i < ALPHABET.length; i++) { | |
INDEXES[ALPHABET[i]] = i; | |
} | |
} | |
/** Encodes the given bytes in base58. No checksum is appended. */ | |
public static String encode(byte[] input) { | |
if (input.length == 0) { | |
return ""; | |
} | |
input = copyOfRange(input, 0, input.length); | |
// Count leading zeroes. | |
int zeroCount = 0; | |
while (zeroCount < input.length && input[zeroCount] == 0) { | |
++zeroCount; | |
} | |
// The actual encoding. | |
byte[] temp = new byte[input.length * 2]; | |
int j = temp.length; | |
int startAt = zeroCount; | |
while (startAt < input.length) { | |
byte mod = divmod58(input, startAt); | |
if (input[startAt] == 0) { | |
++startAt; | |
} | |
temp[--j] = (byte) ALPHABET[mod]; | |
} | |
// Strip extra '1' if there are some after decoding. | |
while (j < temp.length && temp[j] == ALPHABET[0]) { | |
++j; | |
} | |
// Add as many leading '1' as there were leading zeros. | |
while (--zeroCount >= 0) { | |
temp[--j] = (byte) ALPHABET[0]; | |
} | |
byte[] output = copyOfRange(temp, j, temp.length); | |
try { | |
return new String(output, "US-ASCII"); | |
} catch (UnsupportedEncodingException e) { | |
throw new RuntimeException(e); // Cannot happen. | |
} | |
} | |
public static byte[] decode(String input) throws AddressFormatException { | |
if (input.length() == 0) { | |
return new byte[0]; | |
} | |
byte[] input58 = new byte[input.length()]; | |
// Transform the String to a base58 byte sequence | |
for (int i = 0; i < input.length(); ++i) { | |
char c = input.charAt(i); | |
int digit58 = -1; | |
if (c >= 0 && c < 128) { | |
digit58 = INDEXES[c]; | |
} | |
if (digit58 < 0) { | |
throw new AddressFormatException("Illegal character " + c + " at " + i); | |
} | |
input58[i] = (byte) digit58; | |
} | |
// Count leading zeroes | |
int zeroCount = 0; | |
while (zeroCount < input58.length && input58[zeroCount] == 0) { | |
++zeroCount; | |
} | |
// The encoding | |
byte[] temp = new byte[input.length()]; | |
int j = temp.length; | |
int startAt = zeroCount; | |
while (startAt < input58.length) { | |
byte mod = divmod256(input58, startAt); | |
if (input58[startAt] == 0) { | |
++startAt; | |
} | |
temp[--j] = mod; | |
} | |
// Do no add extra leading zeroes, move j to first non null byte. | |
while (j < temp.length && temp[j] == 0) { | |
++j; | |
} | |
return copyOfRange(temp, j - zeroCount, temp.length); | |
} | |
public static BigInteger decodeToBigInteger(String input) throws AddressFormatException { | |
return new BigInteger(1, decode(input)); | |
} | |
/** | |
* Uses the checksum in the last 4 bytes of the decoded data to verify the rest are correct. The checksum is | |
* removed from the returned data. | |
* | |
* @throws AddressFormatException if the input is not base 58 or the checksum does not validate. | |
*/ | |
public static byte[] decodeChecked(String input) throws AddressFormatException { | |
byte tmp [] = decode(input); | |
if (tmp.length < 4) | |
throw new AddressFormatException("Input too short"); | |
byte[] bytes = copyOfRange(tmp, 0, tmp.length - 4); | |
byte[] checksum = copyOfRange(tmp, tmp.length - 4, tmp.length); | |
tmp = Utils.doubleDigest(bytes); | |
byte[] hash = copyOfRange(tmp, 0, 4); | |
if (!Arrays.equals(checksum, hash)) | |
throw new AddressFormatException("Checksum does not validate"); | |
return bytes; | |
} | |
// | |
// number -> number / 58, returns number % 58 | |
// | |
private static byte divmod58(byte[] number, int startAt) { | |
int remainder = 0; | |
for (int i = startAt; i < number.length; i++) { | |
int digit256 = (int) number[i] & 0xFF; | |
int temp = remainder * 256 + digit256; | |
number[i] = (byte) (temp / 58); | |
remainder = temp % 58; | |
} | |
return (byte) remainder; | |
} | |
// | |
// number -> number / 256, returns number % 256 | |
// | |
private static byte divmod256(byte[] number58, int startAt) { | |
int remainder = 0; | |
for (int i = startAt; i < number58.length; i++) { | |
int digit58 = (int) number58[i] & 0xFF; | |
int temp = remainder * 58 + digit58; | |
number58[i] = (byte) (temp / 256); | |
remainder = temp % 256; | |
} | |
return (byte) remainder; | |
} | |
private static byte[] copyOfRange(byte[] source, int from, int to) { | |
byte[] range = new byte[to - from]; | |
System.arraycopy(source, from, range, 0, range.length); | |
return range; | |
} | |
} |
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