Hi,
We would like to discuss a limitation in the current configuration
capabilities for security providers and possible solutions that we are
exploring (†).
As you know, current configuration capabilities in java.security allow
users to install security providers, decide their priority in a list
(security.provider.<n> properties) and even circumvent this priority for
specific algorithms (jdk.security.provider.preferred property). However,
there is no granularity in terms of what service types and algorithms
are enabled once a security provider is installed: it's an all or
nothing scheme. It is worth noting that security providers can bring
with them a diverse range of service types. As an example, the SUN
security provider comes with the following service types: SecureRandom,
Signature, KeyPairGenerator, AlgorithmParameterGenerator,
AlgorithmParameters, KeyFactory, MessageDigest, CertificateFactory,
KeyStore, CertStore, Policy, Configuration, CertPathBuilder and
CertPathValidator [1].
In some cases, the user may need to enforce that all cryptographic
primitives come from a specific security provider. This could happen,
for example, when operating in a FIPS-compliant environment or under
strict security policies. To better illustrate, let's say that the user
requires that all cryptographic operations are performed in a Hardware
Security Module (HSM). On the OpenJDK side, this means that the
implementation for Cipher, Signature, Mac and other cryptographic
services must be the one in the SunPKCS11 security provider. Let's also
suppose that other non-cryptographic services such as those for
certificates validation and TLS are required, and their implementation
is in the SUN and SunJSSE security providers respectively. Setting
SunPKCS11 at the highest priority of the list is not a strong guarantee
to ensure that all cryptographic operations come from it: it's possible
that an algorithm for Signature is not implemented in SunPKCS11 or in
its underlying token but in the SUN security provider. Disabling the SUN
security provider wouldn't be an option in this case because we need its
certificates validation service.
This problem goes beyond OpenJDK default security providers. Even if we
come up with a new layout for service types, algorithms and providers
—putting backward compatibility issues aside—, there is always the
possibility that a 3rd party security provider does not follow any
services grouping convention. It might also be the case that we need to
disable a specific algorithm only —i.e. for cryptographic policy
reasons— and TLS or JAR signing properties fall short.
In our view, it would be beneficial to add more configuration
flexibility and control to the existing API in which any security
provider can be plugged in, in the form of deciding which service types
and algorithms are enabled for each installed provider.
There are 2 alternatives that we are exploring to tackle this problem.
Alternative #1
===========================
Introduce a new security property to decide which service types and
algorithms are enabled for each security provider. The default value for
this property would be empty, which keeps this feature disabled and all
services from installed security providers available.
As for the new property's syntax and semantics, we've been considering
an allow-list along the lines of:
jdk.security.provider.enabled = security-provider-1 { service-type-1 :
alg-1, ... ; ... } , ...
Note: we need a formal syntax specification, this is for illustration only.
As part of the syntax we are considering the use of wildcards (*) to
match multiple security providers, service types and algorithms, and
minus signs (-) to remove service types. When a service type is removed,
the action applies to all algorithms and any attempt to specify them
explicitly would be an error. The minus sign cannot be used at the
algorithm level. We are also thinking that in case of a partial or total
contradiction between conditions, the right-most value applies on top of
the others. If a security provider, service type or algorithm does not
exist, we can simply write a debug warning and ignore it. As for the
name of the algorithms, we can also include Ciphers transformations.
Example:
jdk.security.provider.enabled = * { -Cipher }, SunJCE { Cipher :
AES/GCM/NoPadding, DES ; Signature }, SUN { * ; -Signature }
This would be interpreted as:
* Irrespective of the provider (*), Cipher services should be removed
(-). This rule would be superfluous in this case because the property
itself is an allow-list and there is nothing to the left that enables
Cipher service types for any provider.
* From the SunJCE security provider, Cipher services with
AES/GCM/NoPadding and DES transformations are allowed, and Signature
services with any algorithm are allowed. Notice that there is a shortcut
here: the algorithm list that follows the service name, "': alg-1, ..."
is optional. When omitted all the service's algorithms are enabled.
* From the SUN security provider, every service type is allowed except
Signature (recall that a minus sign can only apply to a service,
removing all associated algorithms).
It's not the goal of this proposal to invalidate property values that
lead to inconsistent internal states, such as "the Cipher service of
SunJCE depends on AlgorithmParameters from SUN". This is because the
combinations for a check are virtually infinite: there can be 3rd party
security providers with their own semantics and dependencies. In the
same way, we cannot determine at start time any application
dependencies. It's up to the user to analyze all types of dependencies
before setting a value.
Alternative #2
===========================
Introduce a boolean security property to turn the value of the existing
jdk.security.provider.preferred property into the only combinations of
algorithm, service and provider that are allowed:
jdk.security.provider.preferredOnly = true
The default value for the new property would be "false", keeping the
current "preferred" behavior in which all algorithms and services from
installed security providers are available.
Contrary to Alternative #1, the user has to explicitly list the
algorithms and cannot rely on wildcards to express wide categories such
as "all Cipher algorithms from SunJCE" or "all algorithms from SunJCE".
The use of minus signs to remove service types or algorithms wouldn't be
available either.
In order to mitigate the burden on users we can consider extending
jdk.security.provider.preferred syntax as long as we keep
backward-compatibility and stay within the boundaries of a "preferred"
semantics. For example, we can accept a value of
"jdk.security.provider.preferred=SunJCE" to mean that any service and
any algorithm from SunJCE is either preferred or allowed, depending on
the value of jdk.security.provider.preferredOnly. This case would be a
service type and algorithm wildcard. We can also define an
algorithms-only wildcard, such as Cipher.*:SunJCE.
Alternative #2 has the advantage of reusing most or all of the existing
syntax. However, it's worth noticing that it implies an overloaded
semantic that can turn confusing or inconvenient in some cases. As an
example, a user that relies on the prioritized security providers list
for most of the algorithms and has only a few preferred exceptions,
would need to express preferences by extension upon turning on this
feature. Alternative #1 keeps preferences and availability as two
separate concepts, in a more clear way.
Thanks,
Martin.-
--
[1] -
https://docs.oracle.com/en/java/javase/17/security/oracle-providers.html#GUID-3A80CC46-91E1-4E47-AC51-CB7B782CEA7D
(†) - Thanks to @fferrari for his contributions to this proposal.
