Mega Code Archive
Base32 encodingdecoding class
<![CDATA[
/* (PD) 2001 The Bitzi Corporation
* Please see http://bitzi.com/publicdomain for more info.
*
* Base32.java
*
* As modified by Jacob Davies:
*
* Copyright © 2010, Data Base Architects, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* * Neither the names of Kalinda Software, DBA Software, Data Base Architects,
* Itemscript nor the names
* of its contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
* SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*/
//package org.itemscript.core.util;
/**
* Base32 encoding/decoding class.
*
* @author Robert Kaye & Gordon Mohr
*/
public final class Base32 {
/* lookup table used to encode() groups of 5 bits of data */
private static final String base32Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
/* lookup table used to decode() characters in Base32 strings */
private static final byte[] base32Lookup = { 26, 27, 28, 29, 30, 31, -1,
-1, -1, -1, -1, -1, -1, -1, // 23456789:;<=>?
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, // @ABCDEFGHIJKLMNO
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, // PQRSTUVWXYZ[\]^_
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, // `abcdefghijklmno
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 // pqrstuvwxyz
};
/* Messsages for Illegal Parameter Exceptions in decode() */
private static final String errorCanonicalLength = "non canonical Base32 string length";
private static final String errorCanonicalEnd = "non canonical bits at end of Base32 string";
private static final String errorInvalidChar = "invalid character in Base32 string";
/**
* Decode a Base32 string into an array of binary bytes. May fail if the
* parameter is a non canonical Base32 string (the only other possible
* exception is that the returned array cannot be allocated in memory)
*/
static public byte[] decode(final String base32)
throws IllegalArgumentException {
// Note that the code below detects could detect non canonical
// Base32 length within the loop. However canonical Base32 length
// can be tested before entering the loop.
// A canonical Base32 length modulo 8 cannot be:
// 1 (aborts discarding 5 bits at STEP n=0 which produces no byte),
// 3 (aborts discarding 7 bits at STEP n=2 which produces no byte),
// 6 (aborts discarding 6 bits at STEP n=1 which produces no byte)
// So these tests could be avoided within the loop.
switch (base32.length() % 8) { // test the length of last subblock
case 1: // 5 bits in subblock: 0 useful bits but 5 discarded
case 3: // 15 bits in subblock: 8 useful bits but 7 discarded
case 6: // 30 bits in subblock: 24 useful bits but 6 discarded
throw new IllegalArgumentException(errorCanonicalLength);
}
byte[] bytes = new byte[base32.length() * 5 / 8];
int offset = 0, i = 0, lookup;
byte nextByte, digit;
// Also the code below does test that other discarded bits
// (1 to 4 bits at end) are effectively 0.
while (i < base32.length()) {
// Read the 1st char in a 8-chars subblock
// check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 0: leave 5 bits
nextByte = (byte) (digit << 3);
// Assert(i < base32.length) // tested before loop
// Read the 2nd char in a 8-chars subblock
// Check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 5: insert 3 bits, leave 2 bits
bytes[offset++] = (byte) (nextByte | (digit >> 2));
nextByte = (byte) ((digit & 3) << 6);
if (i >= base32.length()) {
if (nextByte != (byte) 0) {
throw new IllegalArgumentException(errorCanonicalEnd);
}
break; // discard the remaining 2 bits
}
// Read the 3rd char in a 8-chars subblock
// Check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 2: leave 7 bits
nextByte |= (byte) (digit << 1);
// Assert(i < base32.length) // tested before loop
// Read the 4th char in a 8-chars subblock
// Check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 7: insert 1 bit, leave 4 bits
bytes[offset++] = (byte) (nextByte | (digit >> 4));
nextByte = (byte) ((digit & 15) << 4);
if (i >= base32.length()) {
if (nextByte != (byte) 0) {
throw new IllegalArgumentException(errorCanonicalEnd);
}
break; // discard the remaining 4 bits
}
// Read the 5th char in a 8-chars subblock
// Assert that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 4: insert 4 bits, leave 1 bit
bytes[offset++] = (byte) (nextByte | (digit >> 1));
nextByte = (byte) ((digit & 1) << 7);
if (i >= base32.length()) {
if (nextByte != (byte) 0) {
throw new IllegalArgumentException(errorCanonicalEnd);
}
break; // discard the remaining 1 bit
}
// Read the 6th char in a 8-chars subblock
// Check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 1: leave 6 bits
nextByte |= (byte) (digit << 2);
// Assert(i < base32.length) // tested before loop
// Read the 7th char in a 8-chars subblock
// Check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 6: insert 2 bits, leave 3 bits
bytes[offset++] = (byte) (nextByte | (digit >> 3));
nextByte = (byte) ((digit & 7) << 5);
if (i >= base32.length()) {
if (nextByte != (byte) 0) {
throw new IllegalArgumentException(errorCanonicalEnd);
}
break; // discard the remaining 3 bits
}
// Read the 8th char in a 8-chars subblock
// Check that chars are not outside the lookup table and valid
lookup = base32.charAt(i++) - '2';
if (lookup < 0 || lookup >= base32Lookup.length) {
throw new IllegalArgumentException(errorInvalidChar);
}
digit = base32Lookup[lookup];
if (digit == -1) {
throw new IllegalArgumentException(errorInvalidChar);
}
// // STEP n = 3: insert 5 bits, leave 0 bit
bytes[offset++] = (byte) (nextByte | digit);
// // possible end of string here with no trailing bits
}
// On loop exit, discard trialing n bits.
return bytes;
}
/**
* Encode an array of binary bytes into a Base32 string. Should not fail
* (the only possible exception is that the returned string cannot be
* allocated in memory)
*/
static public String encode(final byte[] bytes) {
StringBuffer base32 = new StringBuffer((bytes.length * 8 + 4) / 5);
int currByte, digit, i = 0;
while (i < bytes.length) {
// INVARIANTS FOR EACH STEP n in [0..5[; digit in [0..31[;
// The remaining n bits are already aligned on top positions
// of the 5 least bits of digit, the other bits are 0.
// //// STEP n = 0; insert new 5 bits, leave 3 bits
currByte = bytes[i++] & 255;
base32.append(base32Chars.charAt(currByte >> 3));
digit = (currByte & 7) << 2;
if (i >= bytes.length) { // put the last 3 bits
base32.append(base32Chars.charAt(digit));
break;
}
// //// STEP n = 3: insert 2 new bits, then 5 bits, leave 1 bit
currByte = bytes[i++] & 255;
base32.append(base32Chars.charAt(digit | (currByte >> 6)));
base32.append(base32Chars.charAt((currByte >> 1) & 31));
digit = (currByte & 1) << 4;
if (i >= bytes.length) { // put the last 1 bit
base32.append(base32Chars.charAt(digit));
break;
}
// //// STEP n = 1: insert 4 new bits, leave 4 bit
currByte = bytes[i++] & 255;
base32.append(base32Chars.charAt(digit | (currByte >> 4)));
digit = (currByte & 15) << 1;
if (i >= bytes.length) { // put the last 4 bits
base32.append(base32Chars.charAt(digit));
break;
}
// //// STEP n = 4: insert 1 new bit, then 5 bits, leave 2 bits
currByte = bytes[i++] & 255;
base32.append(base32Chars.charAt(digit | (currByte >> 7)));
base32.append(base32Chars.charAt((currByte >> 2) & 31));
digit = (currByte & 3) << 3;
if (i >= bytes.length) { // put the last 2 bits
base32.append(base32Chars.charAt(digit));
break;
}
// /// STEP n = 2: insert 3 new bits, then 5 bits, leave 0 bit
currByte = bytes[i++] & 255;
base32.append(base32Chars.charAt(digit | (currByte >> 5)));
base32.append(base32Chars.charAt(currByte & 31));
// // This point is reached for bytes.length multiple of 5
}
return base32.toString();
}
}
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