## net.i2p.crypto
Class HMACGenerator

    java.lang.Object
      net.i2p.crypto.HMACGenerator

Direct Known Subclasses:
  HMAC256Generator

    public class HMACGenerator

extends Object

Calculate the HMAC-MD5-128 of a key+message. All the good stuff occurs in `I2PHMac` and `MD5Digest`. Keys are always 32 bytes. This is used only by UDP. Use deprecated outside the router, this may move to router.jar. NOTE THIS IS NOT COMPATIBLE with javax.crypto.Mac.getInstance("HmacMD5") as we tell I2PHMac that the digest length is 32 bytes, so it generates a different result. Quote jrandom: "The HMAC is hardcoded to use SHA256 digest size for backwards compatability. next time we have a backwards incompatible change, we should update this." Does this mean he intended it to be compatible with MD5? See also 2005-07-05 status notes.

Field Summary
`protected LinkedBlockingQueue<I2PHMac>` `_available` set of available HMAC instances for calculate

Constructor Summary
`HMACGenerator(I2PAppContext context)`

Method Summary
`protected I2PHMac` `acquire()`
`Hash` `calculate(SessionKey key, byte[] data)` Deprecated. unused
`void` `calculate(SessionKey key, byte[] data, int offset, int length, byte[] target, int targetOffset)` Calculate the HMAC of the data with the given 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 java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### _available

    protected final LinkedBlockingQueue<I2PHMac> _available

  set of available HMAC instances for calculate

Constructor Detail

### HMACGenerator

    public HMACGenerator(I2PAppContext context)

Parameters:
  `context` - unused

Method Detail

### calculate

    public Hash calculate(SessionKey key,
                          byte[] data)

  Deprecated. unused

  Calculate the HMAC of the data with the given key

  Returns:
    the first 16 bytes contain the HMAC, the last 16 bytes are zero

### 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

### 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.

  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

### acquire

    protected I2PHMac acquire()