Add testMaxPlaintextLength to check GCM plaintext limits

[SalusaSecondus]

This adds a test to ensure implementations enforce maximum plaintext lengths as defined by NIST SP 800-38D.

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[SalusaSecondus]

I signed it! (I'm covered by Amazon.com's corporate CLA.)

[googlebot]

CLAs look good, thanks!

[cryptosubtlety]

Thanks SalusaSecondus, this is one of few @slowtest tests that we haven't published yet and we'll publish them after the holidays.
FYI, I found this GCM bug in Bouncy Castle (CVE-2015-6644) and OpenJDK8 which lead to the following fixes:
BouncyCastle (https://android.googlesource.com/platform/external/bouncycastle/+/3e128c5fea3a0ca2d372aa09c4fd4bb0eadfbd3f%5E%21/#F0)
OpenJDK8 (http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/rev/0c3ed12cdaf5)

[SalusaSecondus]

So you're the person to thank. Thank you! I did check to ensure the libraries were patched before I made this test public.

I'm starting to think we may need a better way to coordinate to avoid duplicate work. I've a few more tests that I want to draft for AesGcm (and possibly AesEax) but don't know what will pass yet and don't want to write tests you've already spent time on.

[thaidn]

I'm starting to think we may need a better way to coordinate to avoid duplicate work. I've a few more tests that I want to draft for AesGcm (and possibly AesEax) but don't know what will pass yet and don't want to write tests you've already spent time on.

This is awesome :).

Could you please email wycheproof-users@? We can tell you right away what has been done.

[thaidn]

The test that Quan alluded to earlier has been released: https://github.com/google/wycheproof/blob/master/java/com/google/security/wycheproof/testcases/AesGcmTest.java#L452.

Please reopen this PR if you think that test is not quite the same as yours.

Thanks!