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<div class="moz-cite-prefix">Hi Michael,</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I don't know anything about
bureaucrats, I am an engineer. You may need to consult someone
else on bureaucrats. <br>
</div>
<p>I apologize for my apparent deficiencies in this area, but would
you mind explaining how Cipher.wrap() is either supposed to take a
public key and create an encapsulation based on it and return a
secret key implicitly in one clean move, or why it even makes
sense to do so. The method was never conceived as providing the
functionality for what a KEM actually does, and when I did the
initial PKCS11 implementation at Eracom in the late 90's and the
team at Sun added the wrap/unwrap functions to support it, this is
definitely not was intended either - it was for explicit key
wrapping based on the key that was passed to Cipher.init().</p>
<p>On BC's part, we've already implemented RFC 5990/SP 800-56B in
Java and the experience has, at best, been awkward. The new
algorithms have moved awkward to inappropriate. With the new
algorithms, there's no longer only one case of this, it's not an
outlier, there should be a general way of supporting KEMs in the
API that doesn't involve over engineering KeyGenerator and Cipher.<br>
</p>
<p>I work with a team that has had to implement all of them and had
to make them fit into the JCA. We have done so. Like John, I am
simply relaying our experience. In about 18 months these
algorithms are going to become mandatory, what all of us think is
irrelevant. We, for our part, already have a solution, but we both
realize it's not "the solution" - we recognize that the JVM is
uniquely positioned to provide leadership on this and provide a
universal way of doing it.<br>
</p>
<p>Of course, if it's felt that these algorithms should be ignored,
it's not my place to revolt, although I do feel obliged to argue.
I will simply try and do the best by my users, as I have no doubt
will John. Both of us have simply offered our comments in good
faith and to alert the community that things have changed and that
with these new algorithms there is room for a new approach. The
ambiguity about how these algorithms can be implemented and the
excessive need to fallback on propritary classes for them does
suggest that there are some additions to the JCA which would help.
I appreciate to understand this statement does involve actually
understanding what these algorithms do and may require some
additional reading. <br>
</p>
<p>As I said, I'm an engineer, my users will be able to use these
algorithms properly, my team will ensure that, as I have no doubt
will John's. What John and myself, apparently mistakenly, care
about is that our users should also be able to use these
algorithms portably.</p>
<p>Are you saying portability is no longer a consideration?<br>
</p>
<p>Regards,</p>
<p>David<br>
</p>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">On 21/8/22 02:23, Michael StJohns
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:783df5b7-e30f-08e7-dbc3-e3d95f427c18@comcast.net">
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<div class="moz-cite-prefix">Hi David/John -</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I would submit that you're trying too
hard to make your life simple! :-)</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Cipher.wrap/unwrap are the correct
methods.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">For example: <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Cipher kem = Cipher.getInstance
("ECIES/GCM-128-64/KDF-SP800-108-COUNTER-SHA256");</div>
<div class="moz-cite-prefix">kem.init (Cipher.WRAP_MODE, pubkey);</div>
<div class="moz-cite-prefix">byte[] opaqueEncapsulatedKey =
kem.wrap (someOtherKey);</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">The "opaqueEncapsulatedKey" would
contain the data needed by the unwrap function - specifically a)
the ecies ephemeral public key, b) the fact that the derived key
is a GCM key of length 128 and that the GCM tag is 64 bytes
long, c) the KDF, d) (optional) any mixins other than defaults
required by the KDF - which would be passed in a parameter blob
during init. Cipher would NOT return the underlying generated
secret used to wrap the key. Just the public part of the key
pair used to do the ECDH operation against the passed in public
key. In the RSA case, the wrapped encrypting secret would be
an opaque data blob and would be part of the data passed to the
unwrap function.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">If you want a key generated for other
purposes, then the right thing is using a KDF and a Key
agreement function in tandem. Strangely the KDF appears in the
javacard API for 3.1, but not in the JCE/JDK API.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">"What's the difference between a
bureaucrat and an engineer? A bureaucrat takes small solvable
pieces and combines them into one insoluble mass."</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">In this case, Java provides a number
of flexible primitives that can be combined as needed. In this
case, the underlying Cipher implementation would wrap key
agreement and kdf and cipher (GCM) instances. It should return
UnsupportedOperationException for all operations execept
wrap/unwrap and the appropriate init methods.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Later, Mike<br>
</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">On 8/19/2022 6:38 PM, David Hook
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:d511fabf-74dd-ec49-b686-a90eca14861a@cryptoworkshop.com">
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<div class="moz-cite-prefix">Hi Mike,</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">KEMs can be used for key wrapping -
we've actually implemented support for this too. But they are
not actually key wrapping ciphers.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Here's a simple example of using
Kyber for key wrapping in BC:</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">
<pre style="background-color:#ffffff;color:#080808;font-family:'JetBrains Mono',monospace;font-size:11.3pt;"><span style="color:#000000;">SecretKey key </span>= <span style="color:#0033b3;">new </span>SecretKeySpec(<span style="color:#000000;">keyBytes</span>, <span style="color:#067d17;">"AES"</span>);
<span style="color:#000000;">w1</span>.init(<span style="color:#000000;">Cipher</span>.<span style="color:#871094;font-style:italic;">WRAP_MODE</span>, kp.getPublic(), <span style="color:#0033b3;">new </span>KEMParameterSpec(<span style="color:#067d17;">"AES-KWP"</span>));
<span style="color:#0033b3;">byte</span>[] <span style="color:#000000;">data </span>= <span style="color:#000000;">w1</span>.wrap(<span style="color:#000000;">key</span>);
<span style="color:#000000;">Cipher w2 </span>= <span style="color:#000000;">Cipher</span>.<span style="font-style:italic;">getInstance</span>(algorithm, <span style="color:#067d17;">"BCPQC"</span>);
<span style="color:#000000;">w2</span>.init(<span style="color:#000000;">Cipher</span>.<span style="color:#871094;font-style:italic;">UNWRAP_MODE</span>, kp.getPrivate(), <span style="color:#0033b3;">new </span>KEMParameterSpec(<span style="color:#067d17;">"AES-KWP"</span>));
<span style="color:#000000;">Key k </span>= <span style="color:#000000;">w2</span>.unwrap(<span style="color:#000000;">data</span>, <span style="color:#067d17;">"AES"</span>, <span style="color:#000000;">Cipher</span>.<span style="color:#871094;font-style:italic;">SECRET_KEY</span>);
The behavior in this case is in line with what is given in RFC 5990 for the RSA KEM. How it works is by using the key generated
by the KEM to create an AES-KWP key, which is then used to wrap keyBytes. The shortcoming is it means you have to generate the
secret key separately.
This is the problem though - a KEM can actually be used to generate a secret key for other purposes. For example, where
someone is trying to implement a hybrid KAS scheme. But there is currently no mechanism in the Java APIs for being able to
take advantage of this directly, hence our use of the KeyGenerator class and other people's attempts to make use of the KeyAgreement
class. The Cipher.wrap() returns a byte[] - to be used with a KEM for secret generation it would also have to return the
generated secret (I would probably also argue that passing a public key to wrap in order to generate an encapsulation of a
generated encrypted secret was not the correct use of the API either, but the fact remains a byte[] is not really going to cut it).
If you have any further questions, please feel free to ask. For what it is worth, I have been developing providers for the JCE/JCA since
the late 90's and am actually one of the people responsible for the introduction of the existing wrap/unwrap API in the Cipher class.
Thanks,
David
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<div class="moz-cite-prefix">On 20/8/22 07:53, Mike StJohns
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:814F78E4-9932-427B-8B65-1AFE5F9D32E2@comcast.net">
<pre class="moz-quote-pre" wrap="">Hi This implemented as part of Javax.crypto.Cipher. See the Java doc for the wrap and unwrap methods.
Mike
Sent from my iPad
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">On Aug 19, 2022, at 12:56, John Gray <a class="moz-txt-link-rfc2396E" href="mailto:John.Gray@entrust.com" moz-do-not-send="true"><John.Gray@entrust.com></a> wrote:
We are starting to make use of the new PQ algorithms adopted by NIST for prototyping and development of standards. In particular we are working on a composite KEM standard:
See: <a class="moz-txt-link-freetext" href="https://datatracker.ietf.org/doc/draft-ounsworth-pq-composite-kem/" moz-do-not-send="true">https://datatracker.ietf.org/doc/draft-ounsworth-pq-composite-kem/</a>
However, there is no KEM interface in the JCA (which make sense because these are new algorithms, although RSA-KEM has been out since 2010).
I can add one into our toolkit (and I think David may have already added on into BC), but I assume at some point there will be an official one added in Java and likely it won't be identical to what we do even if it is very close, which would cause backwards compatibility pain... Perhaps we could collaborate on extending the JCA to support KEM? Essentially it requires methods.
ss, ct := encapsulate(PublicKey)
ss := decapsulate(PrivateKey, ct)
-ss is a shared secret (could come back as a Java SecretKey if you wanted as it would usually be used to derive something like an AES afterwards)
-ct is a Cipher Text (a byte array would make sense)
-Public and Private Keys would use the regular public and private key interface.
-An object holding the ss and ct from the encapsulate() method could be returned, with accessor methods to get the ss and ct. It could be called 'EncapsulatedKEMData' for example.
Likely you would want a new type of KEM crypto object (like you have for Signature, MessageDigest, Cipher, Mac, SecureRandom, KeyAgreement.. etc). Calling it KEM would seem to make sense. 😊 It could also use similar calling patterns and have a KEM.initKEM(keypair.getPublic()) or KEM.initKEM(keypair.getPrivate()), and then you would just call KEM.encapsulate() or KEM.decapsulate(ct).
Then algorithms could be registered in providers as usual:
put("KEM.Kyber","com.blah.Kyber")
put("KEM.compositeKEM","com.entrust.toolkit.crypto.kem.compositeKEM")
Then the above methods (encapsulate and decapsulate) could be defined in that new object type. Then we would be able to make use of it and not have to worry about incompatibility issues down the road...
Cheers,
John Gray
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