On 8/17/2017 7:01 PM, Xuelei Fan wrote:
On 8/17/2017 11:35 AM, Michael StJohns wrote:
On 8/17/2017 1:28 PM, Xuelei Fan wrote:
This is the same for ANY current publicly known curve - different
providers may implement all some or none of them. So extending
this model for the curve25519 stuff isn't going to be any different
old provider and new provider wise than is currently the case. If
you want the new curves, you have to specify the new providers. If
the new and old providers don't implement the same curves, you may
need to deal with two different providers simultaneously - and
that's not something that just happens.
I see your points. Not-binding to a provider cause problems;
binding to a provider cause other problems. There are a few
complains on the problems, and impact the real world applications in
practice.
Basically, this is a failing of imagination when the various
getInstance() methods were defined. Now its possible to use
Security.getProvider(Map<String,String>) to good effect (but more
work) to find appropriate providers for appropriate signature/key
agreement algorithms and curves.
I'm not sure how this applies to the compatibility impact concern.
See more in the example bellow.
I don't think your concerns are valid. I may still be missing
something here - but would ask for a real-world example that
actually shows breakage.
I happened to have a real-world example. See
https://bugs.openjdk.java.net/browse/JDK-8064330
I'm not sure how this applies to the current question of whether or
not its possible to integrate new EC curves?
This is an interesting bug. At first it is requested to support
SHA224 in JSSE implementation. And, SHA224 is added as the supported
hash algorithm for TLS. However, because SunMSCAPI does not support
SHA224 signature, compatibility issues comes. So we removed SHA224
if the SunMSCAPI is presented. Later, one found the code is unusual
as SHA224 and the related signature algorithms are supported by the
underlying providers, look like no reason to limit the use of
SHA224. So, SHA224 is added back and then the compatibility issues
come back again. Then we removed SHA224 again if the SunMSCAPI is
presented. However, at the same time, another request is asking to
support SHA224 on Windows. The API design itself put me in a
either-or situation. I would try to avoid it if possible for new
design.
This appears to be an MSCAPI issue vice a JSSE issue.
MSCAPI is fine as it does not support SHA224. JSSE is then in a bad
position because it cannot support SHA224 in a general way even one of
the underlying provider supports SHA224 but another one not.
No - I don't think both are fine. MSCAPI could outsource algorithms it
doesn't have internally to another provider - for a very limited set of
classes (e.g. MessageDigest and Secure Random), but it would be smarter
if JSSE just tried to see of the provider it was already using for other
stuff had the available algorithm (e.g. using the long form of getInstance).
In the above case - MSCAPI should realize that it can't do a
SHA224with... signature and just throw the appropriate error. JSSE
should know which TLS suites MSCAPI can support. Or at least be able to
figure out which ones it supports by checking which JCA algorithms are
supported.
And the JCA specifically disclaims the guaranteed ability to use
cryptographic objects from one provider in another provider.
It's not the real problem. The real problem is that there is a
provider support the requested algorithms, why not use it? We can
say, the spec does not guarantee the behavior, but the application
still has a problem. We also can say, we have a design flaw, but the
question is still there.
There is no design flaw, there is only incorrect programming. Basically,
the only non-key related crypto algorithms in the providers are hashing
and random number generation. While its possible to use these across
providers (and you might want to), special casing things to do this
means (for example) that your FIPS approved signature mechanism might
end up using a non-fips summary (hash) mechanism.
Every other crypto mechanism has or involves keys. And there's no
guarantee that keys are valid across providers.
Secondary users like the JSSE probably need to stick to a single
provider for a given connection.
Stick to a single provider will open other windows for different
problems. JCE spec does not grant one provider could implement all
services.
An application that needs to use two different cryptographic algorithm
providers should be doing that explicitly and not having it happen under
the covers. For example, I was using the BC provider to deal with
elliptic curve stuff for a long while. That meant I was also using BC
to deal with certificates (because the Sun provider didn't understand
how to deal with the BC's ECKey implementation). It was kind of a
surprise at the time, but made me quite a bit more cautious about making
sure I didn't leave the selection of the provider up to Java if I was
doing anything remotely complicated.
Mostly a given provider has to implement all of the concrete classes
that support a given class of key material - key generation, signatures,
encryption etc. Given the internal representation of the concrete
classes can be anything I wouldn't expect a key generated by provider A
to work with provider B without some conversion taking place. In both
the RSA and EC key spaces, I can convert a key to a spec, then then back
to a key with minimal problems. The spec contains ALL of the
information I need to get a mathematically correct key out the back
side. Those keys (mostly the public ones) just work because under the
covers good providers are running alien keys through a KeyFactory to get
local keys they can use.
Treat these simply as new curves and let's move forward with very
minimal changes to the public API.
I would like to treat it as two things. One is to support new
curves for new forms. The other one is to support named curves
[1]. For the support of new forms, there are still significant
problems to solve. For the support of named curves (including the
current EC form), looks like we are in a not-that-bad situation
right now. Will the named curves solution impacts the support of
new curves APIs in the future? I don't see the impact yet. I may
missing something, but I see no reason to option out the named
curves support.
I'm not sure why you think this (the example in [1]) can't be done?
I gave the example elsewhere, but let me expand it with my comment
above (possibly faking the hash key names - sorry):
HashMap<String,String> neededAlgs = new HashMap<>();
neededAlgs.put("Signature.EdDSA", "");
neededAlgs.put("AlgorithmParameters.EC SupportedCurves",
"ed25519")
Provider[] p = Security.getProviders(neededAlgs);
if (p == null) throw new Exception ("Oops");
AlgorithmParameters parameters =
AlgorithmParameters.getInstance("EC", p[0]);
parameters.init(new ECGenParameterSpec("ed25519"));
ECParameterSpec ecParameters =
parameters.getParameterSpec(ECParameterSpec.class);
return KeyFactory.getInstance("EC",
p[0]).generatePublic(new ECPublicKeySpec(new ECPoint(x, y),
ecParameters));
Hm, good example!
But it is really too weight to use for general application development.
Umm.. right now about 90+% of the EC stuff focuses on one of the NIST
curves and pretty much all providers implement those. But - the set of
curves that SunEC supports is different than the set of curves that
BouncyCastle supports and I have to take that in consideration when
picking the curve and the provider for my application.
I can either know which provider has which curves up front (or assume
they all have the most common curves) and pick the right provider and
hard code it (and that will work mostly), or use something like the
above and just have it work going forward.
In the example, two crypto operations ("EC" AlgorithmParameters and
"EC" KeyFactory) are supported in the same provider. In practice,
two crypto operations may be supported in different providers.
Actually, in this specific case you COULD use different providers - but
they'd both have to understand what was in the ECParameterSpec in a
non-proprietary way. The first (AlgorithmParameter) provider would
generate an ECParameterSpec which the second provider (the KeyFactory
provider) would convert into a concrete public key (along with the other
data). Sort of the definition of the use of 'Spec classes.
In the above example, I know this works with the SunEC provider for the
AlgorithmParameter side - but I'm pretty sure it doesn't work for the
BouncyCastle side.
If you're talking more generally, NamedCurves should be a form of
ECParameterSpec so you can read the name from the key, but there's no
support for adding names to that spec. Maybe extend it? E.g.:
package java.security.spec;
public class NamedECParameterSpec extends ECParameterSpec {
private Collection<String> names;
private Collection<Oid> oids;
public NamedECParameterSpec (EllipticCurve curve, ECPoint g,
BigInteger n, int h, Collection<String> names, Collection<Oid> oids) {
super (curve, g, n, h);
if (names != null) {
this.names = new ArrayList<String>(names);
}
if (oids != null) {
this.oids = new ArrayList<Oid>(oids);
}
}
public Collection<String> getNames() {
if (names == null)
return (Collection<String>)Collections.EMPTY_LIST;
else
return Collections.unmodifiableList(names);
}
etc....
This makes it easier to get exactly what you want from a key.
Assuming the provider implements it.
I see your points. But my concerns are not really about it. Except
the confusing and possibility to map/convert Montgomery curve or
Edwards curve or other forms [3][4] to Weierstrass form, I did not see
how the new proposal solve the problems I described in the previous
mails [1][2].
If by [1] you mean "There is no public api for named curves" - I would
say that the above actually does provide part of that solution. There
are a number of times when I'm trying to convert a public key from Java
to a smart card where I need to know the curve. Being able to grab the
curve name directly from the ECKey->ECParameterSpec would be useful. If
you mean there is no lookup by name to get direct to an ECParameterSpec
- sure, but there are two work arounds. The one in [1] and the other
involving generating a key pair using ECGenParameterSpec with the curve
name and then grabbing the ECParameterSpec from it. The latter works
with all providers, but seems clumsy.
I actually think the above solves a bunch of what you want for [2].
((NamedECParameterSpec)pubKey.getParameterSpec()).getNames()
Your idea in section 4 of [2] makes me uncomfortable as it *really*
changes the model for parameter based keys (EC, DSA and the new stuff).
Would you move all of the old key and curves over to a new key type?
(E.g. the OKPKey stuff). Would you carry over all the backwards
compatibility stuff (e.g. the complete set of curve parameters needed
for the math) in those keys? If not would you require additional curves
to be accessible both the old and new ways?
The current stuff for Security.getProviders(Map<String,String> filters)
does what you want in section 4 - just in a few more lines.
Later, Mike
Xuelei
[1]:
http://mail.openjdk.java.net/pipermail/security-dev/2013-October/009105.html
[2]:
http://mail.openjdk.java.net/pipermail/security-dev/2017-August/016194.html
[3]: https://crypto.stanford.edu/pbc/notes/elliptic/explicit.html
[4]: http://mathworld.wolfram.com/EllipticCurve.html
