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/*
* Copyright © 2017-2018 WireGuard LLC. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0
*/
package com.wireguard.crypto;
import java.util.Arrays;
/**
* Represents a WireGuard public or private key. This class uses specialized constant-time base64
* and hexadecimal codec implementations that resist side-channel attacks.
* <p>
* Instances of this class are immutable.
*/
@SuppressWarnings("MagicNumber")
public final class Key {
private final byte[] key;
/**
* Constructs an object encapsulating the supplied key.
*
* @param key an array of bytes containing a binary key. Callers of this constructor are
* responsible for ensuring that the array is of the correct length.
*/
private Key(final byte[] key) {
// Defensively copy to ensure immutability.
this.key = Arrays.copyOf(key, key.length);
}
/**
* Decodes a single 4-character base64 chunk to an integer in constant time.
*
* @param src an array of at least 4 characters in base64 format
* @param srcOffset the offset of the beginning of the chunk in {@code src}
* @return the decoded 3-byte integer, or some arbitrary integer value if the input was not
* valid base64
*/
private static int decodeBase64(final char[] src, final int srcOffset) {
int val = 0;
for (int i = 0; i < 4; ++i) {
final char c = src[i + srcOffset];
val |= (-1
+ ((((('A' - 1) - c) & (c - ('Z' + 1))) >>> 8) & (c - 64))
+ ((((('a' - 1) - c) & (c - ('z' + 1))) >>> 8) & (c - 70))
+ ((((('0' - 1) - c) & (c - ('9' + 1))) >>> 8) & (c + 5))
+ ((((('+' - 1) - c) & (c - ('+' + 1))) >>> 8) & 63)
+ ((((('/' - 1) - c) & (c - ('/' + 1))) >>> 8) & 64)
) << (18 - 6 * i);
}
return val;
}
/**
* Encodes a single 4-character base64 chunk from 3 consecutive bytes in constant time.
*
* @param src an array of at least 3 bytes
* @param srcOffset the offset of the beginning of the chunk in {@code src}
* @param dest an array of at least 4 characters
* @param destOffset the offset of the beginning of the chunk in {@code dest}
*/
private static void encodeBase64(final byte[] src, final int srcOffset,
final char[] dest, final int destOffset) {
final byte[] input = {
(byte) ((src[srcOffset] >>> 2) & 63),
(byte) ((src[srcOffset] << 4 | ((src[1 + srcOffset] & 0xff) >>> 4)) & 63),
(byte) ((src[1 + srcOffset] << 2 | ((src[2 + srcOffset] & 0xff) >>> 6)) & 63),
(byte) ((src[2 + srcOffset]) & 63),
};
for (int i = 0; i < 4; ++i) {
dest[i + destOffset] = (char) (input[i] + 'A'
+ (((25 - input[i]) >>> 8) & 6)
- (((51 - input[i]) >>> 8) & 75)
- (((61 - input[i]) >>> 8) & 15)
+ (((62 - input[i]) >>> 8) & 3));
}
}
/**
* Decodes a WireGuard public or private key from its base64 string representation. This
* function throws a {@link KeyFormatException} if the source string is not well-formed.
*
* @param str the base64 string representation of a WireGuard key
* @return the decoded key encapsulated in an immutable container
*/
public static Key fromBase64(final String str) {
final char[] input = str.toCharArray();
if (input.length != Format.BASE64.length || input[Format.BASE64.length - 1] != '=')
throw new KeyFormatException(Format.BASE64);
final byte[] key = new byte[Format.BINARY.length];
int i;
int ret = 0;
for (i = 0; i < key.length / 3; ++i) {
final int val = decodeBase64(input, i * 4);
ret |= val >>> 31;
key[i * 3] = (byte) ((val >>> 16) & 0xff);
key[i * 3 + 1] = (byte) ((val >>> 8) & 0xff);
key[i * 3 + 2] = (byte) (val & 0xff);
}
final char[] endSegment = {
input[i * 4],
input[i * 4 + 1],
input[i * 4 + 2],
'A',
};
final int val = decodeBase64(endSegment, 0);
ret |= (val >>> 31) | (val & 0xff);
key[i * 3] = (byte) ((val >>> 16) & 0xff);
key[i * 3 + 1] = (byte) ((val >>> 8) & 0xff);
if (ret != 0)
throw new KeyFormatException(Format.BASE64);
return new Key(key);
}
/**
* Wraps a WireGuard public or private key in an immutable container. This function throws a
* {@link KeyFormatException} if the source data is not the correct length.
*
* @param bytes an array of bytes containing a WireGuard key in binary format
* @return the key encapsulated in an immutable container
*/
public static Key fromBytes(final byte[] bytes) {
if (bytes.length != Format.BINARY.length)
throw new KeyFormatException(Format.BINARY);
return new Key(bytes);
}
/**
* Decodes a WireGuard public or private key from its hexadecimal string representation. This
* function throws a {@link KeyFormatException} if the source string is not well-formed.
*
* @param str the hexadecimal string representation of a WireGuard key
* @return the decoded key encapsulated in an immutable container
*/
public static Key fromHex(final String str) {
final char[] input = str.toCharArray();
if (input.length != Format.HEX.length)
throw new KeyFormatException(Format.HEX);
final byte[] key = new byte[Format.BINARY.length];
int ret = 0;
for (int i = 0; i < key.length; ++i) {
int c;
int cNum;
int cNum0;
int cAlpha;
int cAlpha0;
int cVal;
final int cAcc;
c = input[i * 2];
cNum = c ^ 48;
cNum0 = ((cNum - 10) >>> 8) & 0xff;
cAlpha = (c & ~32) - 55;
cAlpha0 = (((cAlpha - 10) ^ (cAlpha - 16)) >>> 8) & 0xff;
ret |= ((cNum0 | cAlpha0) - 1) >>> 8;
cVal = (cNum0 & cNum) | (cAlpha0 & cAlpha);
cAcc = cVal * 16;
c = input[i * 2 + 1];
cNum = c ^ 48;
cNum0 = ((cNum - 10) >>> 8) & 0xff;
cAlpha = (c & ~32) - 55;
cAlpha0 = (((cAlpha - 10) ^ (cAlpha - 16)) >>> 8) & 0xff;
ret |= ((cNum0 | cAlpha0) - 1) >>> 8;
cVal = (cNum0 & cNum) | (cAlpha0 & cAlpha);
key[i] = (byte) (cAcc | cVal);
}
if (ret != 0)
throw new KeyFormatException(Format.HEX);
return new Key(key);
}
/**
* Returns the key as an array of bytes.
*
* @return an array of bytes containing the raw binary key
*/
public byte[] getBytes() {
// Defensively copy to ensure immutability.
return Arrays.copyOf(key, key.length);
}
/**
* Encodes the key to base64.
*
* @return a string containing the encoded key
*/
public String toBase64() {
final char[] output = new char[Format.BASE64.length];
int i;
for (i = 0; i < key.length / 3; ++i)
encodeBase64(key, i * 3, output, i * 4);
final byte[] endSegment = {
key[i * 3],
key[i * 3 + 1],
0,
};
encodeBase64(endSegment, 0, output, i * 4);
output[Format.BASE64.length - 1] = '=';
return new String(output);
}
/**
* Encodes the key to hexadecimal ASCII characters.
*
* @return a string containing the encoded key
*/
public String toHex() {
final char[] output = new char[Format.HEX.length];
for (int i = 0; i < key.length; ++i) {
output[i * 2] = (char) (87 + (key[i] >> 4 & 0xf)
+ ((((key[i] >> 4 & 0xf) - 10) >> 8) & ~38));
output[i * 2 + 1] = (char) (87 + (key[i] & 0xf)
+ ((((key[i] & 0xf) - 10) >> 8) & ~38));
}
return new String(output);
}
/**
* The supported formats for encoding a WireGuard key.
*/
public enum Format {
BASE64(44),
BINARY(32),
HEX(64);
private final int length;
Format(final int length) {
this.length = length;
}
public int getLength() {
return length;
}
}
/**
* An exception thrown when attempting to parse an invalid key (too short, too long, or byte
* data inappropriate for the format). The format being parsed can be accessed with the
* {@link #getFormat} method.
*/
public static final class KeyFormatException extends RuntimeException {
private final Format format;
private KeyFormatException(final Format format) {
this.format = format;
}
public Format getFormat() {
return format;
}
}
}
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