net.i2p.crypto

Class HMAC256Generator

java.lang.Object

net.i2p.crypto.HMACGenerator

net.i2p.crypto.HMAC256Generator

public final class HMAC256Generator
extends HMACGenerator

HMAC-SHA256 message authentication code generator for I2P cryptographic operations. This class provides HMAC-SHA256 calculation using the standard JCA Mac interface, ensuring compatibility with javax.crypto.Mac.getInstance("HmacSHA256"). It offers both one-shot calculation and streaming operations for different use cases.

Key features:

• HMAC-SHA256 algorithm implementation for message authentication
• Thread-safe operation with Mac instance pooling
• Optimized for both small and large data processing
• Integration with I2P's session key management

Compatibility Note: As of 0.9.12, this class uses the standard javax.crypto.Mac implementation for improved security and compatibility.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
(package private) static class	HMAC256Generator.HMACKey Performance-optimized SecretKey implementation for HMAC operations.

Constructor Summary

Constructors

Constructor and Description
HMAC256Generator(I2PAppContext context)

Method Summary

Modifier and Type	Method and Description
(package private) Mac	acquire() Package private for HKDF.
void	calculate(byte[] key, byte[] data, int offset, int length, byte[] target, int targetOffset) Calculate the HMAC of the data with the given key.
void	calculate(SessionKey key, byte[] data, int offset, int length, byte[] target, int targetOffset) Calculate the HMAC of the data with the given key.
(package private) void	release(Mac mac) Mac will be reset and initialized with a zero key.
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 net.i2p.crypto.HMACGenerator

acquireTmp, releaseTmp

Methods inherited from class java.lang.Object

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

Constructor Detail

HMAC256Generator

public HMAC256Generator(I2PAppContext context)

Parameters:

context - unused

Method Detail

acquire

Mac acquire()

Package private for HKDF.

Returns:

cached or Mac.getInstance("HmacSHA256")

calculate

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

Calculate the HMAC of the data with the given key. Outputs 32 bytes to target starting at targetOffset.

Parameters:

key - first 32 bytes used as the key

Throws:

UnsupportedOperationException - if the JVM does not support it

IllegalArgumentException - for bad key or target too small

calculate

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

Calculate the HMAC of the data with the given key. Outputs 32 bytes to target starting at targetOffset.

Specified by:

calculate in class HMACGenerator

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:

UnsupportedOperationException - if the JVM does not support it

IllegalArgumentException - for bad key or target too small

release

void release(Mac mac)

Mac will be reset and initialized with a zero key. Package private for HKDF.

verify

public 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.

Specified by:

verify in class HMACGenerator

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, use 32 for HMAC256