net.i2p.crypto

Class HMACGenerator

java.lang.Object

net.i2p.crypto.HMACGenerator

Direct Known Subclasses:

HMAC256Generator

public abstract class HMACGenerator
extends Object

Abstract base class for HMAC (Hash-based Message Authentication Code) operations. This class provides the foundation for HMAC algorithm implementations used throughout I2P for message authentication and integrity verification. It defines the standard interface for calculating and verifying HMAC values with various hash algorithms.

Key operations include:

• HMAC calculation with given key and message data
• Inline MAC verification for performance optimization
• Support for different hash algorithms (SHA-1, SHA-256)
• Integration with I2P's session key management

Implementation Note: As of 0.9.42, this class serves as an abstract base. See net.i2p.router.transport.udp.SSUHMACGenerator for SSU-specific HMAC implementation and SHA256Generator for Syndie-compatible HMAC operations.

Constructor Summary

Constructors

Constructor and Description
HMACGenerator()

Method Summary

Modifier and Type	Method and Description
protected byte[]	acquireTmp() 32 bytes from the byte array cache.
abstract void	calculate(SessionKey key, byte[] data, int offset, int length, byte[] target, int targetOffset) Calculate the HMAC of the data with the given key
protected void	releaseTmp(byte[] tmp)
abstract boolean	verify(SessionKey key, byte[] curData, int curOffset, int curLength, byte[] origMAC, int origMACOffset, int origMACLength) Verify the MAC inline, reducing some unnecessary memory churn.

Methods inherited from class java.lang.Object

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

Constructor Detail

HMACGenerator

public HMACGenerator()

Method Detail

acquireTmp

protected byte[] acquireTmp()

32 bytes from the byte array cache. Does NOT zero.

calculate

public abstract void calculate(SessionKey key,
                               byte[] data,
                               int offset,
                               int length,
                               byte[] target,
                               int targetOffset)

Calculate the HMAC of the data with the given key

Parameters:

key - the session key

data - the data to HMAC

offset - the starting offset in data

length - the length of data to HMAC

target - out parameter the first 16 bytes contain the HMAC, the last 16 bytes are zero

targetOffset - offset into target to put the hmac

Throws:

IllegalArgumentException - for bad key or target too small

releaseTmp

protected void releaseTmp(byte[] tmp)

verify

public abstract boolean verify(SessionKey key,
                               byte[] curData,
                               int curOffset,
                               int curLength,
                               byte[] origMAC,
                               int origMACOffset,
                               int origMACLength)

Verify the MAC inline, reducing some unnecessary memory churn.

Parameters:

key - session key to verify the MAC with

curData - MAC to verify

curOffset - index into curData to MAC

curLength - how much data in curData do we want to run the HMAC over

origMAC - what do we expect the MAC of curData to equal

origMACOffset - index into origMAC

origMACLength - how much of the MAC do we want to verify

Throws:

IllegalArgumentException - for bad key