This code demonstrates that several ECDH secp384 and ECDH secp521 scenarios that passed on Windows 8.1 now fail on Windows 10 for no obvious reasons. See the Windows 10 program output below for details.

Prerequisite

You need to run \Certs\InstallTestCerts.bat to install the certificates. RemoveTestCerts.bat cleans them up. You don't need to create the PFX file but if you want, CreateTestCerts.bat will do so; git revert to get the original .pfx files again.

Running the sample code snippet

After doing the above, open the solution in visual studio and hit Run. For those without Visual Studio, the /bin/debug/ folder has also been pushed into git.

Program results

For those not having access to Visual Studio, here is the output (the certificates and code is available on GitHub)

Windows 10 output (version NT 10.0.10240.0)

'Test ECC Alice secp521r1 SS' <=> 'Test ECC Bob secp521r1 SS'
> FAILURE < ECDH Keys are different!
SymKey12 = 22-46-6B-15-0F-9B-65-B0-D6-7D-AA-0E-C5-8A-7F-F3-18-1F-5F-62-88-26-90-67-DC-99-1B-98-73-3B-58-FF
SymKey21 = FD-C3-24-27-4C-4C-56-01-62-1E-B2-AE-B1-F6-68-64-61-72-EB-2E-6D-F4-30-21-F1-8A-73-C6-85-38-25-FA
------------------------------
'Test ECC Alice secp384r1 SS' <=> 'Test ECC Bob secp384r1 SS'
> FAILURE < ECDH Keys are different!
SymKey12 = F3-55-B0-72-49-DA-A5-6B-D7-3E-B7-F5-87-E7-4B-D1-20-A1-6E-67-EE-FF-C2-A9-12-E4-B0-20-46-F7-A5-FA
SymKey21 = 8C-63-5E-21-AC-BB-C1-AB-17-73-E2-E9-4D-95-20-07-6A-60-69-B1-E6-3B-18-EA-B6-56-FF-38-9F-F8-46-2F
------------------------------
'Test ECC Alice secp256r1 SS' <=> 'Test ECC Bob secp256r1 SS'
Success, ECDH Keys agree
------------------------------
'Alice secp521 test cert' <=> 'Bob secp521 test cert'
> FAILURE < ECDH Keys are different!
SymKey12 = B3-90-1C-1B-B0-66-BB-D8-A2-46-37-A9-E4-84-1F-FE-B8-ED-14-17-A8-D8-0C-EB-20-A0-98-5F-3A-85-73-3D
SymKey21 = 44-62-AD-3F-DA-D4-7E-17-49-05-C4-22-93-DD-36-B7-0D-28-47-93-E5-D4-63-03-00-BC-F8-99-DF-BA-A3-92
------------------------------
'Alice secp384 test cert' <=> 'Bob secp384 test cert'
Success, ECDH Keys agree
------------------------------
'Alice secp256 test cert' <=> 'Bob secp256 test cert'
Success, ECDH Keys agree
------------------------------
Press any key to exit ...

Windows 8 output (version NT 6.3.9600.0)

'Test ECC Alice secp521r1 SS' <=> 'Test ECC Bob secp521r1 SS'
Success, ECDH Keys agree
------------------------------
'Test ECC Alice secp384r1 SS' <=> 'Test ECC Bob secp384r1 SS'
Success, ECDH Keys agree
------------------------------
'Test ECC Alice secp256r1 SS' <=> 'Test ECC Bob secp256r1 SS'
Success, ECDH Keys agree
------------------------------
'Alice secp521 test cert' <=> 'Bob secp521 test cert'
Success, ECDH Keys agree
------------------------------
'Alice secp384 test cert' <=> 'Bob secp384 test cert'
Success, ECDH Keys agree
------------------------------
'Alice secp256 test cert' <=> 'Bob secp256 test cert'
Success, ECDH Keys agree
------------------------------
Press any key to exit ...	

Other info

This code also supports the question at http://security.stackexchange.com/questions/95631/is-sec-p-384-and-p-521-broken-in-windows-10