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Java 25: Key Derivation Function API (JEP 510) #124

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Java 25: Key Derivation Function API (JEP 510) #124

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56 changes: 56 additions & 0 deletions JavaReleases/src/test/java/pl/mperor/lab/java/Java25.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,14 @@
import org.junit.jupiter.api.Test;
import pl.mperor.lab.common.TestUtils;

import javax.crypto.KDF;
import javax.crypto.SecretKey;
import javax.crypto.spec.HKDFParameterSpec;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Path;
import java.security.GeneralSecurityException;
import java.util.Arrays;
import java.util.NoSuchElementException;

/// Java 25 (September 2025)
Expand Down Expand Up @@ -187,4 +193,54 @@ public void testCompactSourceFileRunsDirectlyViaSourceLauncher() throws IOExcept
output);
}

@Test
public void testHkdfExtractThenExpandDerivesSecretKeyOfRequestedLength() throws GeneralSecurityException {
var kdf = KDF.getInstance("HKDF-SHA256");
byte[] ikm = "shared secret".getBytes(StandardCharsets.UTF_8);
byte[] salt = "a salt value".getBytes(StandardCharsets.UTF_8);
byte[] info = "session key".getBytes(StandardCharsets.UTF_8);

var spec = HKDFParameterSpec.ofExtract().addIKM(ikm).addSalt(salt).thenExpand(info, 32);
SecretKey key = kdf.deriveKey("AES", spec);

Assertions.assertEquals("AES", key.getAlgorithm());
Assertions.assertEquals(32, key.getEncoded().length);
}

@Test
public void testSameInputsDeriveSameKeyDifferentInfoDerivesDifferentKey() throws GeneralSecurityException {
byte[] ikm = "shared secret".getBytes(StandardCharsets.UTF_8);
byte[] salt = "a salt value".getBytes(StandardCharsets.UTF_8);

byte[] keyA = deriveAesKeyBytes(ikm, salt, "session key".getBytes(StandardCharsets.UTF_8));
byte[] keyB = deriveAesKeyBytes(ikm, salt, "session key".getBytes(StandardCharsets.UTF_8));
byte[] keyC = deriveAesKeyBytes(ikm, salt, "other purpose".getBytes(StandardCharsets.UTF_8));

// HKDF is deterministic: identical ikm/salt/info always derive the same key material.
Assertions.assertArrayEquals(keyA, keyB);
// Changing only the context-binding `info` derives an unrelated key, even from the same secret.
Assertions.assertFalse(Arrays.equals(keyA, keyC));
}

private static byte[] deriveAesKeyBytes(byte[] ikm, byte[] salt, byte[] info) throws GeneralSecurityException {
var kdf = KDF.getInstance("HKDF-SHA256");
var spec = HKDFParameterSpec.ofExtract().addIKM(ikm).addSalt(salt).thenExpand(info, 32);
return kdf.deriveKey("AES", spec).getEncoded();
}

@Test
public void testDeriveDataReturnsSameRawBytesAsDeriveKey() throws GeneralSecurityException {
byte[] ikm = "shared secret".getBytes(StandardCharsets.UTF_8);
byte[] salt = "a salt value".getBytes(StandardCharsets.UTF_8);
byte[] info = "session key".getBytes(StandardCharsets.UTF_8);
var spec = HKDFParameterSpec.ofExtract().addIKM(ikm).addSalt(salt).thenExpand(info, 32);

// deriveKey() and deriveData() run the same derivation; deriveKey() only wraps the
// resulting bytes into a SecretKey for a named algorithm, deriveData() hands them back raw.
byte[] rawData = KDF.getInstance("HKDF-SHA256").deriveData(spec);
byte[] keyBytes = KDF.getInstance("HKDF-SHA256").deriveKey("AES", spec).getEncoded();

Assertions.assertArrayEquals(keyBytes, rawData);
}

}
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