Interface HKDFParameterSpec

All Superinterfaces:: AlgorithmParameterSpec

All Known Implementing Classes:: HKDFParameterSpec.Expand, HKDFParameterSpec.Extract, HKDFParameterSpec.ExtractThenExpand

public interface HKDFParameterSpec extends AlgorithmParameterSpec

Parameters for the combined Extract, Expand, or Extract-then-Expand operations of the HMAC-based Key Derivation Function (HKDF). The HKDF function is defined in RFC 5869.

In the Extract and Extract-then-Expand cases, users may call the addIKM and/or addSalt methods repeatedly (and chain these calls). This provides for use-cases where a portion of the input keying material (IKM) resides in a non-extractable SecretKey and the whole IKM cannot be provided as a single object. The same feature is available for salts.

The above feature is particularly useful for "labeled" HKDF Extract used in TLS 1.3 and HPKE, where the IKM consists of concatenated components, which may include both byte arrays and (possibly non-extractable) secret keys.

Examples:

 // this usage depicts the initialization of an HKDF-Extract AlgorithmParameterSpec
 AlgorithmParameterSpec derivationSpec =
             HKDFParameterSpec.ofExtract()
                              .addIKM(label)
                              .addIKM(ikm)
                              .addSalt(salt).extractOnly();

 // this usage depicts the initialization of an HKDF-Expand AlgorithmParameterSpec
 AlgorithmParameterSpec derivationSpec =
             HKDFParameterSpec.expandOnly(prk, info, 32);

 // this usage depicts the initialization of an HKDF-ExtractExpand AlgorithmParameterSpec
 AlgorithmParameterSpec derivationSpec =
             HKDFParameterSpec.ofExtract()
                              .addIKM(ikm)
                              .addSalt(salt).thenExpand(info, 32);

Since:

External Specifications

See Also:

Nested Class Summary

Modifier and Type	Interface	Description
`static final class`	`HKDFParameterSpec.Builder`	This `Builder` builds `Extract` and `ExtractThenExpand` objects.
`static final class`	`HKDFParameterSpec.Expand`	Defines the input parameters of an Expand operation as defined in RFC 5869.
`static final class`	`HKDFParameterSpec.Extract`	Defines the input parameters of an Extract operation as defined in RFC 5869.
`static final class`	`HKDFParameterSpec.ExtractThenExpand`	Defines the input parameters of an Extract-then-Expand operation as defined in RFC 5869.

Method Summary

Modifier and Type	Method	Description
`static HKDFParameterSpec.Expand`	`expandOnly(SecretKey prk, byte[] info, int length)`	Creates an `Expand` object.
`static HKDFParameterSpec.Builder`	`ofExtract()`	Returns a `Builder` for building `Extract` and `ExtractThenExpand` objects.

Method Details

ofExtract

static HKDFParameterSpec.Builder ofExtract()

Returns a Builder for building Extract and ExtractThenExpand objects.

Returns:: a new Builder

expandOnly

static HKDFParameterSpec.Expand expandOnly(SecretKey prk, byte[] info, int length)

Creates an Expand object.

Implementation Note:: HKDF implementations will enforce that the length is not greater than 255 * HMAC length. Implementations will also enforce that the prk argument is at least as many bytes as the HMAC length. Implementations will also enforce that a {code null} info value is treated as zero-length byte array.
Parameters:: prk - the pseudorandom key (PRK); must not be null; info - the optional context and application specific information (may be null); the byte array is cloned to prevent subsequent modification; length - the length of the output keying material (must be greater than 0)
Returns:: an Expand object
Throws:: NullPointerException - if the prk argument is null; IllegalArgumentException - if length is not greater than 0

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https://docs.oracle.com/en/java/javase/25/docs/api/java.base/javax/crypto/spec/HKDFParameterSpec.html