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Diffstat (limited to 'app/src/main/java/com/wireguard/crypto/Key.java')
| -rw-r--r-- | app/src/main/java/com/wireguard/crypto/Key.java | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/app/src/main/java/com/wireguard/crypto/Key.java b/app/src/main/java/com/wireguard/crypto/Key.java new file mode 100644 index 00000000..85146794 --- /dev/null +++ b/app/src/main/java/com/wireguard/crypto/Key.java @@ -0,0 +1,255 @@ +/* + * 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; + } + } +} |