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/*
* Copyright (C) 2019 The Android Open Source Project
*
* 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 android.content.integrity;
import static com.android.internal.util.Preconditions.checkArgument;
/**
* Utils class for simple operations used in integrity module.
*
* @hide
*/
public class IntegrityUtils {
private static final char[] HEX_CHARS = "0123456789ABCDEF".toCharArray();
/**
* Obtain the raw bytes from hex encoded string.
*
* @throws IllegalArgumentException if {@code hexDigest} is not a valid hex encoding of some
* bytes
*/
public static byte[] getBytesFromHexDigest(String hexDigest) {
checkArgument(
hexDigest.length() % 2 == 0,
"Invalid hex encoding %s: must have even length", hexDigest);
byte[] rawBytes = new byte[hexDigest.length() / 2];
for (int i = 0; i < rawBytes.length; i++) {
int upperNibble = hexDigest.charAt(2 * i);
int lowerNibble = hexDigest.charAt(2 * i + 1);
rawBytes[i] = (byte) ((hexToDec(upperNibble) << 4) | hexToDec(lowerNibble));
}
return rawBytes;
}
/** Obtain hex encoded string from raw bytes. */
public static String getHexDigest(byte[] rawBytes) {
char[] hexChars = new char[rawBytes.length * 2];
for (int i = 0; i < rawBytes.length; i++) {
int upperNibble = (rawBytes[i] >>> 4) & 0xF;
int lowerNibble = rawBytes[i] & 0xF;
hexChars[i * 2] = decToHex(upperNibble);
hexChars[i * 2 + 1] = decToHex(lowerNibble);
}
return new String(hexChars);
}
private static int hexToDec(int hexChar) {
if (hexChar >= '0' && hexChar <= '9') {
return hexChar - '0';
}
if (hexChar >= 'a' && hexChar <= 'f') {
return hexChar - 'a' + 10;
}
if (hexChar >= 'A' && hexChar <= 'F') {
return hexChar - 'A' + 10;
}
throw new IllegalArgumentException("Invalid hex char " + hexChar);
}
private static char decToHex(int dec) {
if (dec >= 0 && dec < HEX_CHARS.length) {
return HEX_CHARS[dec];
}
throw new IllegalArgumentException("Invalid dec value to be converted to hex digit " + dec);
}
}
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