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## org.bouncycastle.crypto.generators
Class HKDFBytesGenerator

    java.lang.Object
      org.bouncycastle.crypto.generators.HKDFBytesGenerator

All Implemented Interfaces:
  DerivationFunction

public class HKDFBytesGenerator
extends java.lang.Object
implements DerivationFunction

HMAC-based Extract-and-Expand Key Derivation Function (HKDF) implemented according to IETF RFC 5869, May 2010 as specified by H. Krawczyk, IBM Research & P. Eronen, Nokia. It uses a HMac internally to compute de OKM (output keying material) and is likely to have better security properties than KDF's based on just a hash function.

Constructor Summary
`HKDFBytesGenerator(Digest hash)` Creates a HKDFBytesGenerator based on the given hash function.

Method Summary
`byte[]` | `extractPRK(byte[] salt, byte[] ikm)` Performs the extract part of the key derivation function.
`int` | `generateBytes(byte[] out, int outOff, int len)`
`Digest` | `getDigest()`
`void` | `init(DerivationParameters param)`

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

Constructor Detail

### HKDFBytesGenerator

    public HKDFBytesGenerator(Digest hash)

  Creates a HKDFBytesGenerator based on the given hash function.

Parameters:
  `hash` - the digest to be used as the source of generatedBytes bytes

Method Detail

### init

    public void init(DerivationParameters param)

  Specified by:
    `init` in interface `DerivationFunction`

### extractPRK

    public byte[] extractPRK(byte[] salt,
                             byte[] ikm)

  Performs the extract part of the key derivation function.

  Parameters:
    `salt` - the salt to use
    `ikm` - the input keying material
  Returns:
    the PRK as KeyParameter

### getDigest

    public Digest getDigest()

### generateBytes

    public int generateBytes(byte[] out,
                             int outOff,
                             int len)
                      throws DataLengthException,
                             java.lang.IllegalArgumentException

  Specified by:
    `generateBytes` in interface `DerivationFunction`
  Throws:
    `DataLengthException`
    `java.lang.IllegalArgumentException`

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