RFR: 8368841: X25519 implementation differs from the specification in RFC 7748

[Shawn M Emery]

On Tue, 17 Feb 2026 01:52:57 GMT, Ben Perez <bperez at openjdk.org> wrote:

> Our implementation of X25519 does not zero the MSB of the `u` coordinate as required by RFC 7748. Currently the test `jdk/sun/security/ec/xec/TestXDH.java` zeroes the bit manually while parsing test vectors, which is likely why this went uncaught.

LGTM.
nit: copyright update

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Marked as reviewed by smemery at github.com (no known OpenJDK username).

PR Review: https://git.openjdk.org/jdk/pull/29750#pullrequestreview-3815255772