AbstractOTPGenerator

java.lang.Object

org.cryptacular.generator.AbstractOTPGenerator

Direct Known Subclasses:: HOTPGenerator, TOTPGenerator

public abstract class AbstractOTPGenerator extends Object

Abstract base class for HOTP and TOTP OTP generation schemes.

Field Summary

Fields

Modifier and Type

Field

Description

protected static final int

DEFAULT_NUMBER_OF_DIGITS

Default number of digits to generate.

private static final int[]

MODULUS

Array of modulus values indexed per number of digits in OTP output.

private final int

numberOfDigits

Number of digits in generated OTP.
Constructor Summary

Constructors

Constructor

Description

AbstractOTPGenerator()

Creates a new abstract OTP generator.

AbstractOTPGenerator(int numberOfDigits)

Creates a new abstract OTP generator.
Method Summary

Modifier and Type

Method

Description

protected int

generateInternal(byte[] key, long count)

Internal OTP generation method.

protected abstract org.bouncycastle.crypto.Digest

getDigest()

int

getNumberOfDigits()

private int

truncate(byte[] hmac)

Truncates HMAC output onto an unsigned (i.e.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details
- DEFAULT_NUMBER_OF_DIGITS
  
  protected static final int DEFAULT_NUMBER_OF_DIGITS
  
  Default number of digits to generate.
  See Also:
  
  Constant Field Values
- MODULUS
  
  private static final int[] MODULUS
  
  Array of modulus values indexed per number of digits in OTP output.
- numberOfDigits
  
  private final int numberOfDigits
  
  Number of digits in generated OTP.
Constructor Details
- AbstractOTPGenerator
  
  public AbstractOTPGenerator()
  
  Creates a new abstract OTP generator.
- AbstractOTPGenerator
  
  public AbstractOTPGenerator(int numberOfDigits)
  
  Creates a new abstract OTP generator.
  
  Parameters:
  
  numberOfDigits - Number of digits in generated OTP. MUST be in the range 6 - 9.
Method Details
- getNumberOfDigits
  
  public int getNumberOfDigits()
  
  Returns:
  
  Number of digits in generated OTP.
- generateInternal
  
  protected int generateInternal(byte[] key, long count)
  
  Internal OTP generation method.
  
  Parameters:
  
  key - Per-user key.
  
  count - Counter moving factor.
  
  Returns:
  
  Integer OTP.
- getDigest
  
  protected abstract org.bouncycastle.crypto.Digest getDigest()
  
  Returns:
  
  Digest algorithm used for HMAC operation.
- truncate
  
  private int truncate(byte[] hmac)
  
  Truncates HMAC output onto an unsigned (i.e. 31-bit) integer using the strategy discussed in RFC 4226, section 5.3.
  
  Parameters:
  
  hmac - HMAC output.
  
  Returns:
  
  Truncated output.