com.eatthepath.otp

Class HmacOneTimePasswordGenerator

java.lang.Object

com.eatthepath.otp.HmacOneTimePasswordGenerator

Direct Known Subclasses:

TimeBasedOneTimePasswordGenerator

public class HmacOneTimePasswordGenerator
extends Object

Generates HMAC-based one-time passwords (HOTP) as specified in RFC 4226.

HmacOneTimePasswordGenerator instances are thread-safe and may be shared and re-used across multiple threads.

Author:

Jon Chambers

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_PASSWORD_LENGTH The default length, in decimal digits, for one-time passwords.
static String	HOTP_HMAC_ALGORITHM The HMAC algorithm specified by the HOTP standard.

Constructor Summary

Constructors

Constructor and Description
HmacOneTimePasswordGenerator() Creates a new HMAC-based one-time password (HOTP) generator using a default password length (6 digits).
HmacOneTimePasswordGenerator(int passwordLength) Creates a new HMAC-based one-time password (HOTP) generator using the given password length.

Method Summary

Modifier and Type	Method and Description
int	generateOneTimePassword(Key key, long counter) Generates a one-time password using the given key and counter value.
String	getAlgorithm() Returns the name of the HMAC algorithm used by this generator.
int	getPasswordLength() Returns the length, in decimal digits, of passwords produced by this generator.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_PASSWORD_LENGTH

public static final int DEFAULT_PASSWORD_LENGTH

The default length, in decimal digits, for one-time passwords.

See Also:

Constant Field Values

HOTP_HMAC_ALGORITHM

public static final String HOTP_HMAC_ALGORITHM

The HMAC algorithm specified by the HOTP standard.

See Also:

Constant Field Values

Constructor Detail

HmacOneTimePasswordGenerator

public HmacOneTimePasswordGenerator()
                             throws NoSuchAlgorithmException

Creates a new HMAC-based one-time password (HOTP) generator using a default password length (6 digits).

Throws:

NoSuchAlgorithmException - if the underlying JRE doesn't support the "HmacSHA1" algorithm, which should never happen except in cases of serious misconfiguration

HmacOneTimePasswordGenerator

public HmacOneTimePasswordGenerator(int passwordLength)
                             throws NoSuchAlgorithmException

Creates a new HMAC-based one-time password (HOTP) generator using the given password length.

Parameters:

passwordLength - the length, in decimal digits, of the one-time passwords to be generated; must be between 6 and 8, inclusive

Throws:

NoSuchAlgorithmException - if the underlying JRE doesn't support the "HmacSHA1" algorithm, which should never happen except in cases of serious misconfiguration

Method Detail

generateOneTimePassword

public int generateOneTimePassword(Key key,
                                   long counter)
                            throws InvalidKeyException

Generates a one-time password using the given key and counter value.

Parameters:

key - a secret key to be used to generate the password

counter - the counter value to be used to generate the password

Returns:

an integer representation of a one-time password; callers will need to format the password for display on their own

Throws:

InvalidKeyException - if the given key is inappropriate for initializing the Mac for this generator

getPasswordLength

public int getPasswordLength()

Returns the length, in decimal digits, of passwords produced by this generator.

Returns:

the length, in decimal digits, of passwords produced by this generator

getAlgorithm

public String getAlgorithm()

Returns the name of the HMAC algorithm used by this generator.

Returns:

the name of the HMAC algorithm used by this generator