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HOTP.java
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HOTP.java
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/*
* OneTimePasswordAlgorithm.java
* OATH Initiative,
* HOTP one-time password algorithm
*
*/
/* Copyright (C) 2004, OATH. All rights reserved.
*
* License to copy and use this software is granted provided that it
* is identified as the "OATH HOTP Algorithm" in all material
* mentioning or referencing this software or this function.
*
* License is also granted to make and use derivative works provided
* that such works are identified as
* "derived from OATH HOTP algorithm"
* in all material mentioning or referencing the derived work.
*
* OATH (Open AuTHentication) and its members make no
* representations concerning either the merchantability of this
* software or the suitability of this software for any particular
* purpose.
*
* It is provided "as is" without express or implied warranty
* of any kind and OATH AND ITS MEMBERS EXPRESSaLY DISCLAIMS
* ANY WARRANTY OR LIABILITY OF ANY KIND relating to this software.
*
* These notices must be retained in any copies of any part of this
* documentation and/or software.
*/
//package org.openauthentication.otp;
import java.io.IOException;
import java.io.File;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.lang.reflect.UndeclaredThrowableException;
import java.security.GeneralSecurityException;
import java.security.NoSuchAlgorithmException;
import java.security.InvalidKeyException;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
/**
* This class contains static methods that are used to calculate the
* One-Time Password (OTP) using
* JCE to provide the HMAC-SHA-1.
*
* @author Loren Hart
* @version 1.0
*/
public class OneTimePasswordAlgorithm {
private OneTimePasswordAlgorithm() {
}
// These are used to calculate the check-sum digits.
// 0 1 2 3 4 5 6 7 8 9
private static final int[] doubleDigits = { 0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
/**
* Calculates the checksum using the credit card algorithm.
* This algorithm has the advantage that it detects any single
* mistyped digit and any single transposition of
* adjacent digits.
*
* @param num the number to calculate the checksum for
* @param digits number of significant places in the number
*
* @return the checksum of num
*/
public static int calcChecksum(long num, int digits) {
boolean doubleDigit = true;
int total = 0;
while (0 < digits--) {
int digit = (int) (num % 10);
num /= 10;
if (doubleDigit) {
digit = doubleDigits[digit];
}
total += digit;
doubleDigit = !doubleDigit;
}
int result = total % 10;
if (result > 0) {
result = 10 - result;
}
return result;
}
/**
* This method uses the JCE to provide the HMAC-SHA-1
* M’Raihi, et al. Informational [Page 28]
* RFC 4226 HOTP Algorithm December 2005
* algorithm.
* HMAC computes a Hashed Message Authentication Code and
* in this case SHA1 is the hash algorithm used.
*
* @param keyBytes the bytes to use for the HMAC-SHA-1 key
* @param text the message or text to be authenticated.
*
* @throws NoSuchAlgorithmException if no provider makes
* either HmacSHA1 or HMAC-SHA-1
* digest algorithms available.
* @throws InvalidKeyException
* The secret provided was not a valid
* HMAC-SHA-1 key.
*
*/
public static byte[] hmac_sha1(byte[] keyBytes, byte[] text)
throws NoSuchAlgorithmException, InvalidKeyException {
// try {
Mac hmacSha1;
try {
hmacSha1 = Mac.getInstance("HmacSHA1");
} catch (NoSuchAlgorithmException nsae) {
hmacSha1 = Mac.getInstance("HMAC-SHA-1");
}
SecretKeySpec macKey = new SecretKeySpec(keyBytes, "RAW");
hmacSha1.init(macKey);
return hmacSha1.doFinal(text);
// } catch (GeneralSecurityException gse) {
// throw new UndeclaredThrowableException(gse);
// }
}
private static final int[] DIGITS_POWER
// 0 1 2 3 4 5 6 7 8
= { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000 };
/**
* This method generates an OTP value for the given
* set of parameters.
*
* @param secret the shared secret
* @param movingFactor the counter, time, or other value that
* changes on a per use basis.
* @param codeDigits the number of digits in the OTP, not
* including the checksum, if any.
* @param addChecksum a flag that indicates if a checksum digit
* M’Raihi, et al. Informational [Page 29]
* RFC 4226 HOTP Algorithm December 2005
* should be appended to the OTP.
* @param truncationOffset the offset into the MAC result to
* begin truncation. If this value is out of
* the range of 0 ... 15, then dynamic
* truncation will be used.
* Dynamic truncation is when the last 4
* bits of the last byte of the MAC are
* used to determine the start offset.
* @throws NoSuchAlgorithmException if no provider makes
* either HmacSHA1 or HMAC-SHA-1
* digest algorithms available.
* @throws InvalidKeyException
* The secret provided was not
* a valid HMAC-SHA-1 key.
*
* @return A numeric String in base 10 that includes
* {@link codeDigits} digits plus the optional checksum
* digit if requested.
*/
static public String generateOTP(byte[] secret,
long movingFactor,
int codeDigits,
boolean addChecksum,
int truncationOffset)
throws NoSuchAlgorithmException, InvalidKeyException {
// put movingFactor value into text byte array
String result = null;
int digits = addChecksum ? (codeDigits + 1) : codeDigits;
byte[] text = new byte[8];
for (int i = text.length - 1; i >= 0; i--) {
text[i] = (byte) (movingFactor & 0xff);
movingFactor >>= 8;
}
// compute hmac hash
byte[] hash = hmac_sha1(secret, text);
// put selected bytes into result int
int offset = hash[hash.length - 1] & 0xf;
if ((0 <= truncationOffset) &&
(truncationOffset < (hash.length - 4))) {
offset = truncationOffset;
}
int binary = ((hash[offset] & 0x7f) << 24)
| ((hash[offset + 1] & 0xff) << 16)
| ((hash[offset + 2] & 0xff) << 8)
| (hash[offset + 3] & 0xff);
int otp = binary % DIGITS_POWER[codeDigits];
if (addChecksum) {
otp = (otp * 10) + calcChecksum(otp, codeDigits);
}
result = Integer.toString(otp);
while (result.length() < digits) {
result = "0" + result;
}
return result;
}
}