[8u] RFR: JDK-8258419: RSA cipher buffer cleanup

[Andrew Hughes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8258419
Webrev: https://cr.openjdk.java.net/~andrew/openjdk8/8258419/webrev.01/

This patch cleans up RSA temporary buffers after use and avoids
some unnecessary copying. Fix is backported to all Oracle releases
from 7 to 17.

Patch applies almost cleanly to 8u. Only rejects are the copyright
header changes to RSAPadding.java and RSACipher.java, as they were
already updated to 2020 by JDK-8230978.

Ok for 8u?

Thanks,
-- 
Andrew :)

Senior Free Java Software Engineer
OpenJDK Package Owner
Red Hat, Inc. (http://www.redhat.com)

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