/*******************************************************************************
* Copyright (c) 2006, 2012 IBM Corporation and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.osgi.internal.signedcontent;
public class Base64 {
private static final byte equalSign = (byte) '=';
static char digits[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', //
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', //
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', //
'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'};
/**
* This method decodes the byte array in base 64 encoding into a char array
* Base 64 encoding has to be according to the specification given by the
* RFC 1521 (5.2).
*
* @param data the encoded byte array
* @return the decoded byte array
*/
public static byte[] decode(byte[] data) {
if (data.length == 0)
return data;
int lastRealDataIndex = data.length - 1;
while (data[lastRealDataIndex] == equalSign)
lastRealDataIndex--;
// original data digit is 8 bits long, but base64 digit is 6 bits long
int padBytes = data.length - 1 - lastRealDataIndex;
int byteLength = data.length * 6 / 8 - padBytes;
byte[] result = new byte[byteLength];
// Each 4 bytes of input (encoded) we end up with 3 bytes of output
int dataIndex = 0;
int resultIndex = 0;
int allBits = 0;
// how many result chunks we can process before getting to pad bytes
int resultChunks = (lastRealDataIndex + 1) / 4;
for (int i = 0; i < resultChunks; i++) {
allBits = 0;
// Loop 4 times gathering input bits (4 * 6 = 24)
for (int j = 0; j < 4; j++)
allBits = (allBits << 6) | decodeDigit(data[dataIndex++]);
// Loop 3 times generating output bits (3 * 8 = 24)
for (int j = resultIndex + 2; j >= resultIndex; j--) {
result[j] = (byte) (allBits & 0xff); // Bottom 8 bits
allBits = allBits >>> 8;
}
resultIndex += 3; // processed 3 result bytes
}
// Now we do the extra bytes in case the original (non-encoded) data
// was not multiple of 3 bytes
switch (padBytes) {
case 1 :
// 1 pad byte means 3 (4-1) extra Base64 bytes of input, 18
// bits, of which only 16 are meaningful
// Or: 2 bytes of result data
allBits = 0;
// Loop 3 times gathering input bits
for (int j = 0; j < 3; j++)
allBits = (allBits << 6) | decodeDigit(data[dataIndex++]);
// NOTE - The code below ends up being equivalent to allBits =
// allBits>>>2
// But we code it in a non-optimized way for clarity
// The 4th, missing 6 bits are all 0
allBits = allBits << 6;
// The 3rd, missing 8 bits are all 0
allBits = allBits >>> 8;
// Loop 2 times generating output bits
for (int j = resultIndex + 1; j >= resultIndex; j--) {
result[j] = (byte) (allBits & 0xff); // Bottom 8
// bits
allBits = allBits >>> 8;
}
break;
case 2 :
// 2 pad bytes mean 2 (4-2) extra Base64 bytes of input, 12 bits
// of data, of which only 8 are meaningful
// Or: 1 byte of result data
allBits = 0;
// Loop 2 times gathering input bits
for (int j = 0; j < 2; j++)
allBits = (allBits << 6) | decodeDigit(data[dataIndex++]);
// NOTE - The code below ends up being equivalent to allBits =
// allBits>>>4
// But we code it in a non-optimized way for clarity
// The 3rd and 4th, missing 6 bits are all 0
allBits = allBits << 6;
allBits = allBits << 6;
// The 3rd and 4th, missing 8 bits are all 0
allBits = allBits >>> 8;
allBits = allBits >>> 8;
result[resultIndex] = (byte) (allBits & 0xff); // Bottom
// 8
// bits
break;
}
return result;
}
/**
* This method converts a Base 64 digit to its numeric value.
*
* @param data digit (character) to convert
* @return value for the digit
*/
static int decodeDigit(byte data) {
char charData = (char) data;
if (charData <= 'Z' && charData >= 'A')
return charData - 'A';
if (charData <= 'z' && charData >= 'a')
return charData - 'a' + 26;
if (charData <= '9' && charData >= '0')
return charData - '0' + 52;
switch (charData) {
case '+' :
return 62;
case '/' :
return 63;
default :
throw new IllegalArgumentException("Invalid char to decode: " + data); //$NON-NLS-1$
}
}
/**
* This method encodes the byte array into a char array in base 64 according
* to the specification given by the RFC 1521 (5.2).
*
* @param data the encoded char array
* @return the byte array that needs to be encoded
*/
public static byte[] encode(byte[] data) {
int sourceChunks = data.length / 3;
int len = ((data.length + 2) / 3) * 4;
byte[] result = new byte[len];
int extraBytes = data.length - (sourceChunks * 3);
// Each 4 bytes of input (encoded) we end up with 3 bytes of output
int dataIndex = 0;
int resultIndex = 0;
int allBits = 0;
for (int i = 0; i < sourceChunks; i++) {
allBits = 0;
// Loop 3 times gathering input bits (3 * 8 = 24)
for (int j = 0; j < 3; j++)
allBits = (allBits << 8) | (data[dataIndex++] & 0xff);
// Loop 4 times generating output bits (4 * 6 = 24)
for (int j = resultIndex + 3; j >= resultIndex; j--) {
result[j] = (byte) digits[(allBits & 0x3f)]; // Bottom
// 6
// bits
allBits = allBits >>> 6;
}
resultIndex += 4; // processed 4 result bytes
}
// Now we do the extra bytes in case the original (non-encoded) data
// is not multiple of 4 bytes
switch (extraBytes) {
case 1 :
allBits = data[dataIndex++]; // actual byte
allBits = allBits << 8; // 8 bits of zeroes
allBits = allBits << 8; // 8 bits of zeroes
// Loop 4 times generating output bits (4 * 6 = 24)
for (int j = resultIndex + 3; j >= resultIndex; j--) {
result[j] = (byte) digits[(allBits & 0x3f)]; // Bottom
// 6
// bits
allBits = allBits >>> 6;
}
// 2 pad tags
result[result.length - 1] = (byte) '=';
result[result.length - 2] = (byte) '=';
break;
case 2 :
allBits = data[dataIndex++]; // actual byte
allBits = (allBits << 8) | (data[dataIndex++] & 0xff); // actual
// byte
allBits = allBits << 8; // 8 bits of zeroes
// Loop 4 times generating output bits (4 * 6 = 24)
for (int j = resultIndex + 3; j >= resultIndex; j--) {
result[j] = (byte) digits[(allBits & 0x3f)]; // Bottom
// 6
// bits
allBits = allBits >>> 6;
}
// 1 pad tag
result[result.length - 1] = (byte) '=';
break;
}
return result;
}
}
