Package com.amdelamar.jotp.type

Class HOTP

java.lang.Object

com.amdelamar.jotp.type.HOTP

All Implemented Interfaces:

OTPInterface

public class HOTP
extends java.lang.Object
implements OTPInterface

Hmac based OTP class implements OTPInterface

Since:

1.0.0

See Also:

https://tools.ietf.org/html/rfc4226

Constructor Summary

Constructors

Constructor	Description
HOTP()

Method Summary

Modifier and Type	Method	Description
protected static int	checksum(long num, int digits)	Calculates the checksum using the credit card algorithm.
java.lang.String	create(java.lang.String secret, java.lang.String base, int digits)	Create a one-time-password with the given key, base, and digits.
protected static java.lang.String	generateHotp(byte[] secret, long movingFactor, int digits, boolean addChecksum, int truncationOffset, java.lang.String crypto)	This method generates an OTP value for the given set of parameters.
java.lang.String	getLabel()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HOTP

public HOTP()

Method Detail

getLabel

public java.lang.String getLabel()

Specified by:

getLabel in interface OTPInterface

create

public java.lang.String create(java.lang.String secret,
                               java.lang.String base,
                               int digits)
                        throws java.security.InvalidKeyException,
                               java.security.NoSuchAlgorithmException

Create a one-time-password with the given key, base, and digits.

Specified by:

create in interface OTPInterface

Parameters:

secret - The secret. Shhhhhh!

base - The offset. (HOTP is a counter incremented by each use)

digits - The length of the code (Commonly '6')

Returns:

code

Throws:

java.security.NoSuchAlgorithmException - when HMAC is not available on this jvm

java.security.InvalidKeyException - when secret is invalid

See Also:

https://tools.ietf.org/html/rfc4226

checksum

protected static int checksum(long num,
                              int digits)

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.

Parameters:

num - the number to calculate the checksum for

digits - number of significant places in the number

Returns:

the checksum of num

generateHotp

protected static java.lang.String generateHotp(byte[] secret,
                                               long movingFactor,
                                               int digits,
                                               boolean addChecksum,
                                               int truncationOffset,
                                               java.lang.String crypto)
                                        throws java.security.NoSuchAlgorithmException,
                                               java.security.InvalidKeyException

This method generates an OTP value for the given set of parameters.

Parameters:

secret - Shhhhh.

movingFactor - the counter, time, or other value

digits - length of the code

addChecksum - a flag that indicates if the checksum digit should be appened to the OTP

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.

crypto - the crypto function to use

Returns:

An OTP code.

Throws:

java.security.NoSuchAlgorithmException - if hmac sha1 is not available

java.security.InvalidKeyException - if given key is inappropriate for this mac