Class KDF

java.lang.Object

javax.crypto.KDF

public final class KDF extends Object

This class provides the functionality of a Key Derivation Function (KDF), which is a cryptographic algorithm for deriving additional keys from input keying material (IKM) and (optionally) other data.

KDF objects are instantiated with the getInstance family of methods.

The class has two derive methods, deriveKey and deriveData. The deriveKey method accepts an algorithm name and returns a SecretKey object with the specified algorithm. The deriveData method returns a byte array of raw data.

API Usage Example:

    KDF kdfHkdf = KDF.getInstance("HKDF-SHA256");

    AlgorithmParameterSpec derivationSpec =
             HKDFParameterSpec.ofExtract()
                              .addIKM(ikm)
                              .addSalt(salt).thenExpand(info, 32);

    SecretKey sKey = kdfHkdf.deriveKey("AES", derivationSpec);

Concurrent Access

Unless otherwise documented by an implementation, the methods defined in this class are not thread-safe. Multiple threads that need to access a single object concurrently should synchronize amongst themselves and provide the necessary locking. Multiple threads each manipulating separate objects need not synchronize.

Delayed Provider Selection

If a provider is not specified when calling one of the getInstance methods, the implementation delays the selection of the provider until the deriveKey or deriveData method is called. This is called delayed provider selection. The primary reason this is done is to ensure that the selected provider can handle the key material that is passed to those methods - for example, the key material may reside on a hardware device that only a specific KDF provider can utilize. The


 getInstance

method returns a KDF object as long as there exists at least one registered security provider that implements the algorithm and supports the optional parameters. The delayed provider selection process traverses the list of registered security providers, starting with the most preferred Provider. The first provider that supports the specified algorithm, optional parameters, and key material is selected.

If the getProviderName or getParameters method is called before the deriveKey or deriveData methods, the first provider supporting the KDF algorithm and optional KDFParameters is chosen. This provider may not support the key material that is subsequently passed to the deriveKey or deriveData methods. Therefore, it is recommended not to call the getProviderName or getParameters methods until after a key derivation operation. Once a provider is selected, it cannot be changed.

Since:

See Also:

Method Summary

Modifier and Type	Method	Description
`byte[]`	`deriveData(AlgorithmParameterSpec derivationSpec)`	Derives a key, returns raw data as a byte array.
`SecretKey`	`deriveKey(String alg, AlgorithmParameterSpec derivationSpec)`	Derives a key, returned as a `SecretKey` object.
`String`	`getAlgorithm()`	Returns the algorithm name of this `KDF` object.
`static KDF`	`getInstance(String algorithm)`	Returns a `KDF` object that implements the specified algorithm.
`static KDF`	`getInstance(String algorithm, String provider)`	Returns a `KDF` object that implements the specified algorithm from the specified security provider.
`static KDF`	`getInstance(String algorithm, Provider provider)`	Returns a `KDF` object that implements the specified algorithm from the specified security provider.
`static KDF`	`getInstance(String algorithm, KDFParameters kdfParameters)`	Returns a `KDF` object that implements the specified algorithm and is initialized with the specified parameters.
`static KDF`	`getInstance(String algorithm, KDFParameters kdfParameters, String provider)`	Returns a `KDF` object that implements the specified algorithm from the specified provider and is initialized with the specified parameters.
`static KDF`	`getInstance(String algorithm, KDFParameters kdfParameters, Provider provider)`	Returns a `KDF` object that implements the specified algorithm from the specified provider and is initialized with the specified parameters.
`KDFParameters`	`getParameters()`	Returns the `KDFParameters` used with this `KDF` object.
`String`	`getProviderName()`	Returns the name of the provider.

Methods declared in class Object

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

Method Details

getAlgorithm

public String getAlgorithm()

Returns the algorithm name of this KDF object.

Returns:: the algorithm name of this KDF object

getProviderName

public String getProviderName()

Returns the name of the provider.

Returns:

the name of the provider

See Also:

getParameters

public KDFParameters getParameters()

Returns the KDFParameters used with this KDF object.

The returned parameters may be the same that were used to initialize this KDF object, or may contain additional default or random parameter values used by the underlying KDF algorithm. If the required parameters were not supplied and can be generated by the KDF object, the generated parameters are returned; otherwise null is returned.

Returns:

the parameters used with this KDF object, or null

See Also:

getInstance

public static KDF getInstance(String algorithm) throws NoSuchAlgorithmException

Returns a KDF object that implements the specified algorithm.

Implementation Note:

The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().

Parameters:

algorithm - the key derivation algorithm to use. See the KDF section in the Java Security Standard Algorithm Names Specification for information about standard KDF algorithm names.

Returns:

a KDF object

Throws:

NoSuchAlgorithmException - if no Provider supports a KDF implementation for the specified algorithm

NullPointerException - if algorithm is null

External Specifications

See Also:

getInstance

public static KDF getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException

Returns a KDF object that implements the specified algorithm from the specified security provider. The specified provider must be registered in the security provider list.

Parameters:

algorithm - the key derivation algorithm to use. See the KDF section in the Java Security Standard Algorithm Names Specification for information about standard KDF algorithm names.

provider - the provider to use for this key derivation

Returns:

a KDF object

Throws:

NoSuchAlgorithmException - if the specified provider does not support the specified KDF algorithm

NoSuchProviderException - if the specified provider is not registered in the security provider list

NullPointerException - if algorithm or provider is null

External Specifications

getInstance

public static KDF getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException

Returns a KDF object that implements the specified algorithm from the specified security provider.

Parameters:

algorithm - the key derivation algorithm to use. See the KDF section in the Java Security Standard Algorithm Names Specification for information about standard KDF algorithm names.

provider - the provider to use for this key derivation

Returns:

a KDF object

Throws:

NoSuchAlgorithmException - if the specified provider does not support the specified KDF algorithm

NullPointerException - if algorithm or provider is null

External Specifications

getInstance

public static KDF getInstance(String algorithm, KDFParameters kdfParameters) throws NoSuchAlgorithmException, InvalidAlgorithmParameterException

Returns a KDF object that implements the specified algorithm and is initialized with the specified parameters.

Implementation Note:

Parameters:

algorithm - the key derivation algorithm to use. See the KDF section in the Java Security Standard Algorithm Names Specification for information about standard KDF algorithm names.

kdfParameters - the KDFParameters used to configure the derivation algorithm or null if no parameters are provided

Returns:

a KDF object

Throws:

NoSuchAlgorithmException - if no Provider supports a KDF implementation for the specified algorithm

InvalidAlgorithmParameterException - if at least one Provider supports a KDF implementation for the specified algorithm but none of them support the specified parameters

NullPointerException - if algorithm is null

External Specifications

See Also:

getInstance

public static KDF getInstance(String algorithm, KDFParameters kdfParameters, String provider) throws NoSuchAlgorithmException, NoSuchProviderException, InvalidAlgorithmParameterException

Returns a KDF object that implements the specified algorithm from the specified provider and is initialized with the specified parameters. The specified provider must be registered in the security provider list.

Parameters:

algorithm - the key derivation algorithm to use. See the KDF section in the Java Security Standard Algorithm Names Specification for information about standard KDF algorithm names.

kdfParameters - the KDFParameters used to configure the derivation algorithm or null if no parameters are provided

provider - the provider to use for this key derivation

Returns:

a KDF object

Throws:

NoSuchAlgorithmException - if the specified provider does not support the specified KDF algorithm

NoSuchProviderException - if the specified provider is not registered in the security provider list

InvalidAlgorithmParameterException - if the specified provider supports the specified KDF algorithm but does not support the specified parameters

NullPointerException - if algorithm or provider is null

External Specifications

getInstance

public static KDF getInstance(String algorithm, KDFParameters kdfParameters, Provider provider) throws NoSuchAlgorithmException, InvalidAlgorithmParameterException

Returns a KDF object that implements the specified algorithm from the specified provider and is initialized with the specified parameters.

Parameters:

algorithm - the key derivation algorithm to use. See the KDF section in the Java Security Standard Algorithm Names Specification for information about standard KDF algorithm names.

kdfParameters - the KDFParameters used to configure the derivation algorithm or null if no parameters are provided

provider - the provider to use for this key derivation

Returns:

a KDF object

Throws:

NoSuchAlgorithmException - if the specified provider does not support the specified KDF algorithm

InvalidAlgorithmParameterException - if the specified provider supports the specified KDF algorithm but does not support the specified parameters

NullPointerException - if algorithm or provider is null

External Specifications

deriveKey

public SecretKey deriveKey(String alg, AlgorithmParameterSpec derivationSpec) throws InvalidAlgorithmParameterException, NoSuchAlgorithmException

Derives a key, returned as a SecretKey object.

Parameters:

alg - the algorithm of the resultant SecretKey object. See the SecretKey Algorithms section in the Java Security Standard Algorithm Names Specification for information about standard secret key algorithm names.

derivationSpec - the object describing the inputs to the derivation function

Returns:

the derived key

Throws:

InvalidAlgorithmParameterException - if the information contained within the derivationSpec is invalid or if the combination of alg and the derivationSpec results in something invalid

NoSuchAlgorithmException - if alg is empty or invalid

NullPointerException - if alg or derivationSpec is null

External Specifications

See Also:

deriveData

public byte[] deriveData(AlgorithmParameterSpec derivationSpec) throws InvalidAlgorithmParameterException

Derives a key, returns raw data as a byte array.

Parameters:

derivationSpec - the object describing the inputs to the derivation function

Returns:

the derived key in its raw bytes

Throws:

InvalidAlgorithmParameterException - if the information contained within the derivationSpec is invalid

UnsupportedOperationException - if the derived keying material is not extractable

NullPointerException - if derivationSpec is null

See Also:

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