HMAC256Generator (Javadocs [I2P+ 2.13.0+]

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.

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)
Create a new HMAC256Generator.

Constructors
Constructor and Description
`HMAC256Generator(I2PAppContext context)` Create a new HMAC256Generator.

Method Summary

All Methods Instance Methods Concrete Methods
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)` Release a Mac back to the pool.
`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)
```
    Create a new HMAC256Generator.
    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
    data - the data to calculate the HMAC over
    offset - offset into data
    length - number of bytes to include
    target - output buffer
    targetOffset - offset into target
    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
    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)
```
    Release a Mac back to the pool. Mac will be reset and initialized with a zero key. Package private for HKDF.
    Parameters:
    mac - the Mac to release
  - 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
    Returns:
    true if the MAC matches

Class HMAC256Generator

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class net.i2p.crypto.HMACGenerator

Methods inherited from class java.lang.Object

Constructor Detail

HMAC256Generator

Method Detail

acquire

calculate

calculate

release

verify