RFR: 8311170: Simplify and modernize equals and hashCode in security area [v3]

[Daniel Jeliński]

On Tue, 4 Jul 2023 16:27:05 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> Please review this PR to use modern APIs and language features to simplify `equals` and `hashCode` in security area.
>> 
>> I understand that security area is sensitive and a non-expert, such as myself, should tread carefully; so below are my notes to assist the review.
>> 
>> * Unlike `hashCode`, non-secure `equals` implementations are typically short-circuit. But because of "timing attacks", we seem to have specialized implementations, such as `java.security.MessageDigest.isEqual(byte[], byte[])` and a more general `sun.security.util.ByteArrays.isEqual(byte[], int, int, byte[], int, int)`. So while reviewing this PR, take an opportunity to audit the affected `equals` implementations: perhaps some of them need to become secure, not modern. I have no domain knowledge to tell those cases apart, I only note that those cases exist.
>> 
>> * This PR sacrifices compatibility for pragmatism: it changes some `hashCode` implementations to produce different values than before to allow more utilization of methods from `Objects` and `Arrays`. To my mind, those changes are **benign**. If you disagree, I'd be happy to discuss that and/or retract the concerning part of the change.
>> 
>> * BitArray could be a topic of its own, but I'll do my best to be concise.
>> 
>>     * Truth to be told, BitArray's `equals` and `hashCode` are not used anywhere in source, and `equals` is only used in one test. For that reason, I refrained from reimplementing internals of `BitArray` using more general `java.util.BitSet`: too much effort and risk for almost nothing.
>>     * Speaking of `BitSet`-powered `BitArray`. Such an implementation is not for the faint of heart: there's too much impedance mismatch between data structures that those classes use to store bits. That said, for the sake of testing that it is possible and that I understand the `BitArray` correctly, I actually implemented it using `BitSet`. While that implementation is **NOT** part of this PR, you can have a look at it [here](https://cr.openjdk.org/~prappo/8311170/BitArray.java).
>> 
>> * One suggestion to consider is to change this somewhat arcane piece in java.security.UnresolvedPermission.equals:
>> 
>>           // check certs
>>           if (this.certs == null && that.certs != null ||
>>               this.certs != null && that.certs == null ||
>>               this.certs != null &&
>>                  this.certs.length != that.certs.length) {
>>               return false;
>>           }
>>   
>>           int i,j;
>>           boolea...
>
> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add even more cases and tidy up

src/java.base/share/classes/java/security/spec/ECFieldF2m.java line 235:

> 233:     public int hashCode() {
> 234:         int value = m << 5;
> 235:         // consider simplifying using Objects.hashCode(rp) after JDK-8015417

Could you explain this comment? Why does it apply here, and not to other methods like CodeSigner.hashCode?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14738#discussion_r1253038416