Class Hkdf

java.lang.Object

org.conscrypt.Hkdf

public final class Hkdf
extends Object

Hkdf - perform HKDF key derivation operations per RFC 5869.

Instances should be instantiated using the standard JCA name for the required HMAC.

Each invocation of expand or extract uses a new Mac instance and so instances of Hkdf are thread-safe.

Field Summary

Fields

Modifier and Type	Field	Description
private final String	hmacName
private final int	macLength

Constructor Summary

Constructors

Constructor	Description
Hkdf(String hmacName)	Creates an Hkdf instance which will use hmacName as the name for the underlying HMAC algorithm, which will be located using normal JCA precedence rules.

Method Summary

Modifier and Type	Method	Description
byte[]	expand(byte[] prk, byte[] info, int length)	Performs an HKDF expand operation as specified in RFC 5869.
byte[]	extract(byte[] salt, byte[] ikm)	Performs an HKDF extract operation as specified in RFC 5869.
private Mac	getMac(byte[] key)
int	getMacLength()

Methods inherited from class Object

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

Field Details

hmacName

private final String hmacName

macLength

private final int macLength

Constructor Details

Hkdf

public Hkdf(String hmacName)
     throws NoSuchAlgorithmException

Creates an Hkdf instance which will use hmacName as the name for the underlying HMAC algorithm, which will be located using normal JCA precedence rules.

Parameters:

hmacName - the name of the HMAC algorithm to use

Throws:

NoSuchAlgorithmException - if hmacName is not a valid HMAC name

Method Details

getMacLength

public int getMacLength()

extract

public byte[] extract(byte[] salt,
 byte[] ikm)
               throws InvalidKeyException,
NoSuchAlgorithmException

Performs an HKDF extract operation as specified in RFC 5869.

Parameters:

salt - the salt to use

ikm - initial keying material

Returns:

a pseudorandom key suitable for use in expand operations

Throws:

InvalidKeyException - if the salt is not suitable for use as an HMAC key

NoSuchAlgorithmException - if the Mac algorithm is no longer available

expand

public byte[] expand(byte[] prk,
 byte[] info,
 int length)
              throws InvalidKeyException,
NoSuchAlgorithmException

Performs an HKDF expand operation as specified in RFC 5869.

Parameters:

prk - a pseudorandom key of at least HashLen octets, usually the output from the extract step. Where HashLen is the key size of the underlying Mac

info - optional context and application specific information, can be zero length

length - length of output keying material in bytes (invalid input: '<'= 255*HashLen)

Returns:

output of keying material of length bytes

Throws:

InvalidKeyException - if prk is not suitable for use as an HMAC key

IllegalArgumentException - if length is out of the allowed range

NoSuchAlgorithmException - if the Mac algorithm is no longer available

getMac

private Mac getMac(byte[] key)
            throws InvalidKeyException,
NoSuchAlgorithmException

Throws:

InvalidKeyException

NoSuchAlgorithmException