net.i2p.crypto

Class HKDF

java.lang.Object

net.i2p.crypto.HKDF

public final class HKDF
extends Object

HMAC-based Key Derivation Function (HKDF) implementation using HMAC-SHA256. This class implements the HKDF algorithm as specified in RFC 5869 for deriving cryptographic keys from input key material. It provides secure key expansion functionality essential for I2P's cryptographic operations including session key generation and key derivation.

Features and capabilities:

• HMAC-SHA256 based derivation for cryptographic security
• Support for one or two output keys with optional info parameter
• Thread-safe operation with no internal state
• Fixed 32-byte output size for consistency across I2P
• Reusable instances for performance optimization

See Also:

RFC 5869 - HKDF

Constructor Summary

Constructors

Constructor and Description
HKDF(I2PAppContext context)

Method Summary

Modifier and Type	Method and Description
void	calculate(byte[] key, byte[] data, byte[] out) One output, no info.
void	calculate(byte[] key, byte[] data, byte[] out, byte[] out2, int off2) Two outputs, no info.
void	calculate(byte[] key, byte[] data, String info, byte[] out) One output with info.
void	calculate(byte[] key, byte[] data, String info, byte[] out, byte[] out2, int off2) Two outputs with info.

Methods inherited from class java.lang.Object

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

Constructor Detail

HKDF

public HKDF(I2PAppContext context)

Parameters:

context - the app context

Method Detail

calculate

public void calculate(byte[] key,
                      byte[] data,
                      byte[] out)

One output, no info.

Parameters:

key - first 32 bytes used as the key

data - the input data

out - must be exactly 32 bytes

calculate

public void calculate(byte[] key,
                      byte[] data,
                      byte[] out,
                      byte[] out2,
                      int off2)

Two outputs, no info.

Parameters:

key - first 32 bytes used as the key

out - 32 bytes will be copied to here

out2 - 32 bytes will be copied to here, may be the same as out

off2 - offset for copy to out2

calculate

public void calculate(byte[] key,
                      byte[] data,
                      String info,
                      byte[] out)

One output with info.

Parameters:

key - first 32 bytes used as the key

data - the input data

info - non-null ASCII, "" if none

out - must be exactly 32 bytes

calculate

public void calculate(byte[] key,
                      byte[] data,
                      String info,
                      byte[] out,
                      byte[] out2,
                      int off2)

Two outputs with info.

Parameters:

key - first 32 bytes used as the key

info - non-null ASCII, "" if none

out - 32 bytes will be copied to here

out2 - 32 bytes will be copied to here, may be the same as out

off2 - offset for copy to out2