Hi Michael,
I don't know anything about bureaucrats, I am an engineer. You may need
to consult someone else on bureaucrats.
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().
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.
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.
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.
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.
Are you saying portability is no longer a consideration?
Regards,
David
On 21/8/22 02:23, Michael StJohns wrote:
Hi David/John -
I would submit that you're trying too hard to make your life simple! :-)
Cipher.wrap/unwrap are the correct methods.
For example:
Cipher kem = Cipher.getInstance
("ECIES/GCM-128-64/KDF-SP800-108-COUNTER-SHA256");
kem.init (Cipher.WRAP_MODE, pubkey);
byte[] opaqueEncapsulatedKey = kem.wrap (someOtherKey);
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.
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.
"What's the difference between a bureaucrat and an engineer? A
bureaucrat takes small solvable pieces and combines them into one
insoluble mass."
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.
Later, Mike
On 8/19/2022 6:38 PM, David Hook wrote:
Hi Mike,
KEMs can be used for key wrapping - we've actually implemented
support for this too. But they are not actually key wrapping ciphers.
Here's a simple example of using Kyber for key wrapping in BC:
SecretKey key =new SecretKeySpec(keyBytes,"AES");
w1.init(Cipher.WRAP_MODE, kp.getPublic(),new KEMParameterSpec("AES-KWP"));
byte[]data =w1.wrap(key);
Cipher w2 =Cipher.getInstance(algorithm,"BCPQC");
w2.init(Cipher.UNWRAP_MODE, kp.getPrivate(),new KEMParameterSpec("AES-KWP"));
Key k =w2.unwrap(data,"AES",Cipher.SECRET_KEY);
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
On 20/8/22 07:53, Mike StJohns wrote:
Hi This implemented as part of Javax.crypto.Cipher. See the Java doc for the
wrap and unwrap methods.
Mike
Sent from my iPad
On Aug 19, 2022, at 12:56, John Gray<john.g...@entrust.com> 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:https://datatracker.ietf.org/doc/draft-ounsworth-pq-composite-kem/
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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