/**
* 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 org.syncany.util;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
/**
* <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>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>
*
* @see <a href="https://code.google.com/p/bitcoinj/source/browse/lib/src/com/google/bitcoin/core/Base58.java?r=216deb2d35d1a128a7f617b91f2ca35438aae546">Original source of this class</a>
* @author Mike Hearn
*/
public class Base58 {
public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
private static final int[] INDEXES = new int[128];
private static final MessageDigest digest;
static {
try {
digest = MessageDigest.getInstance("SHA-256");
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e); // Can't happen.
}
}
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) {
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 IllegalArgumentException("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);
}
/**
* @see #doubleDigest(byte[], int, int)
*/
public static byte[] doubleDigest(byte[] input) {
return doubleDigest(input, 0, input.length);
}
/**
* Calculates the SHA-256 hash of the given byte range, and then hashes the resulting hash again. This is
* standard procedure in Bitcoin. The resulting hash is in big endian form.
*/
public static byte[] doubleDigest(byte[] input, int offset, int length) {
synchronized (digest) {
digest.reset();
digest.update(input, offset, length);
byte[] first = digest.digest();
return digest.digest(first);
}
}
//
// 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;
}
}