jrihtarsic commented on code in PR #298:
URL: https://github.com/apache/ws-wss4j/pull/298#discussion_r1531940269
##########
ws-security-dom/src/main/java/org/apache/wss4j/dom/message/WSSecEncryptedKey.java:
##########
@@ -561,6 +581,56 @@ private KeyAgreementParameters
buildKeyAgreementParameter(PublicKey recipientPub
return dhSpec;
}
+ /**
+ * Method builds the KeyDerivationParameters for keyDerivationMethod and
default values. The default values for
+ * the key derivation method are:
+ * <ul>
+ * <li>ConcatKDF
+ * <ul>
+ * <li> DigestAlgorithm:
"http://www.w3.org/2001/04/xmlenc#sha256";</li>
+ * <li> AlgorithmID: "0000"</li>
+ * <li> PartyUInfo: ""</li>
+ * <li> PartyVInfo: ""</li>
+ * <li> SuppPubInfo: null</li>
+ * <li> SuppPrivInfo: null</li>
+ * </ul>
+ * <li>HKDF: SHA-256
+ * <ul>
+ * <li> PRF: http://www.w3.org/2001/04/xmldsig-more#hmac-sha256 </li>
+ * <li> Salt: random 256 bit value</li>
+ * <li> Info: null</li>
+ * </ul>
+ * </li>
+ * </ul>
+ *
+ * @param keyBitLength the length of the derived key in bits
+ * @return KeyDerivationParameters the {@link KeyDerivationParameters} for
generating the
+ * key for encrypting transport key and generating XML elements.
+ * @throws WSSecurityException if the KeyDerivationParameters cannot be
created
+ */
+ private KeyDerivationParameters buildKeyDerivationParameters(int
keyBitLength) throws WSSecurityException {
+
+ switch (keyDerivationMethod) {
+ case WSS4JConstants.KEYDERIVATION_CONCATKDF:
+ return
XMLCipherUtil.constructConcatKeyDerivationParameter(keyBitLength,
WSConstants.SHA256,
+ "0000", "", "", null, null);
+ case WSS4JConstants.KEYDERIVATION_HKDF:
+ // use semi random value for salt.
+ // rfc5869: Yet, even a salt value of less quality (shorter in
+ // size or with limited entropy) may still make a significant
+ // contribution to the security of the output keying material
+ byte[] semiRandom = new byte[keyBitLength / 8];
+ new Random().nextBytes(semiRandom);
Review Comment:
Sure.
As you can see from rfc5869:
[3.1](https://datatracker.ietf.org/doc/html/rfc5869#section-3.1). To Salt or
not to Salt
> Yet, even a salt value of less quality (shorter in
> size or with limited entropy) may still make a significant
> contribution to the security of the output keying material.
In this case (for the HKDF), the salt is public, and it doesn't matter if
it's made from high or limited entropy, but it makes a difference as long as
it's there.
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