org.tomitribe.util.Base32 Maven / Gradle / Ivy
/*
* Taken with small modifications
*
* Copyright 2009 Google Inc. All Rights Reserved.
*
* 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.tomitribe.util;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Locale;
/**
* Encodes arbitrary byte arrays as case-insensitive base-32 strings.
*
* The implementation is slightly different than in RFC 4648. During encoding,
* padding is not added, and during decoding the last incomplete chunk is not
* taken into account. The result is that multiple strings decode to the same
* byte array, for example, string of sixteen 7s ("7...7") and seventeen 7s both
* decode to the same byte array.
*
* @author [email protected] (Steve Weis)
* @author Neal Gafter
*/
public class Base32 {
// singleton
private static final int SECRET_SIZE = 10;
private static final SecureRandom RANDOM = new SecureRandom();
private static final Base32 INSTANCE =
new Base32("ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"); // RFC 4648/3548
static Base32 getInstance() {
return INSTANCE;
}
// 32 alpha-numeric characters.
private String ALPHABET;
private char[] DIGITS;
private int MASK;
private int SHIFT;
private HashMap CHAR_MAP;
static final String SEPARATOR = "-";
protected Base32(String alphabet) {
this.ALPHABET = alphabet;
DIGITS = ALPHABET.toCharArray();
MASK = DIGITS.length - 1;
SHIFT = Integer.numberOfTrailingZeros(DIGITS.length);
CHAR_MAP = new HashMap();
for (int i = 0; i < DIGITS.length; i++) {
CHAR_MAP.put(DIGITS[i], i);
}
}
public static byte[] decode(String encoded) throws DecodingException {
return getInstance().decodeInternal(encoded);
}
protected byte[] decodeInternal(String encoded) throws DecodingException {
// Remove whitespace and separators
encoded = encoded.trim().replaceAll(SEPARATOR, "").replaceAll(" ", "");
// Remove padding. Note: the padding is used as hint to determine how many
// bits to decode from the last incomplete chunk (which is commented out
// below, so this may have been wrong to start with).
encoded = encoded.replaceFirst("[=]*$", "");
// Canonicalize to all upper case
encoded = encoded.toUpperCase(Locale.US);
if (encoded.length() == 0) {
return new byte[0];
}
int encodedLength = encoded.length();
int outLength = encodedLength * SHIFT / 8;
byte[] result = new byte[outLength];
int buffer = 0;
int next = 0;
int bitsLeft = 0;
for (char c : encoded.toCharArray()) {
if (!CHAR_MAP.containsKey(c)) {
throw new DecodingException("Illegal character: " + c);
}
buffer <<= SHIFT;
buffer |= CHAR_MAP.get(c) & MASK;
bitsLeft += SHIFT;
if (bitsLeft >= 8) {
result[next++] = (byte) (buffer >> (bitsLeft - 8));
bitsLeft -= 8;
}
}
// We'll ignore leftover bits for now.
//
// if (next != outLength || bitsLeft >= SHIFT) {
// throw new DecodingException("Bits left: " + bitsLeft);
// }
return result;
}
public static String encode(byte[] data) {
return getInstance().encodeInternal(data);
}
protected String encodeInternal(byte[] data) {
if (data.length == 0) {
return "";
}
// SHIFT is the number of bits per output character, so the length of the
// output is the length of the input multiplied by 8/SHIFT, rounded up.
if (data.length >= (1 << 28)) {
// The computation below will fail, so don't do it.
throw new IllegalArgumentException();
}
int outputLength = (data.length * 8 + SHIFT - 1) / SHIFT;
StringBuilder result = new StringBuilder(outputLength);
int buffer = data[0];
int next = 1;
int bitsLeft = 8;
while (bitsLeft > 0 || next < data.length) {
if (bitsLeft < SHIFT) {
if (next < data.length) {
buffer <<= 8;
buffer |= (data[next++] & 0xff);
bitsLeft += 8;
} else {
int pad = SHIFT - bitsLeft;
buffer <<= pad;
bitsLeft += pad;
}
}
int index = MASK & (buffer >> (bitsLeft - SHIFT));
bitsLeft -= SHIFT;
result.append(DIGITS[index]);
}
return result.toString();
}
public static class DecodingException extends Exception {
public DecodingException(String message) {
super(message);
}
}
public static String random() {
// Allocating the buffer
byte[] buffer = new byte[SECRET_SIZE];
// Filling the buffer with random numbers.
RANDOM.nextBytes(buffer);
// Getting the key and converting it to Base32
byte[] secretKey = Arrays.copyOf(buffer, SECRET_SIZE);
return encode(secretKey);
}
}