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/*
* Copyright © 2014-2019 The Android Password Store Authors. All Rights Reserved.
* SPDX-License-Identifier: GPL-3.0-only
*/
package com.zeapo.pwdstore.utils;
import java.math.BigInteger;
import java.nio.ByteBuffer;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Base32;
import timber.log.Timber;
public class Otp {
private static final Base32 BASE_32 = new Base32();
private Otp() {}
public static String calculateCode(
String secret, long counter, String algorithm, String digits) {
String[] steam = {
"2", "3", "4", "5", "6", "7", "8", "9", "B", "C", "D", "F", "G", "H", "J", "K", "M",
"N", "P", "Q", "R", "T", "V", "W", "X", "Y"
};
String ALGORITHM = "Hmac" + algorithm.toUpperCase();
SecretKeySpec signingKey = new SecretKeySpec(BASE_32.decode(secret), ALGORITHM);
Mac mac;
try {
mac = Mac.getInstance(ALGORITHM);
mac.init(signingKey);
} catch (NoSuchAlgorithmException e) {
Timber.tag("TOTP").e(e, "%s unavailable - should never happen", ALGORITHM);
return null;
} catch (InvalidKeyException e) {
Timber.tag("TOTP").e(e, "Key is malformed");
return null;
}
byte[] digest = mac.doFinal(ByteBuffer.allocate(8).putLong(counter).array());
int offset = digest[digest.length - 1] & 0xf;
byte[] code = Arrays.copyOfRange(digest, offset, offset + 4);
code[0] = (byte) (0x7f & code[0]);
String strCode = new BigInteger(code).toString();
if (digits.equals("s")) {
StringBuilder output = new StringBuilder();
int bigInt = new BigInteger(code).intValue();
for (int i = 0; i != 5; i++) {
output.append(steam[bigInt % 26]);
bigInt /= 26;
}
return output.toString();
} else return strCode.substring(strCode.length() - Integer.parseInt(digits));
}
}
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