Add SHA-512 support

[fghanmi]

Currently only SHA-256 is supported. But, some clients are heavily dependent on SHA-512.
This issue is to track the implementation of SHA-512 support in tough.

[sumukhballal]

Thank you for opening this issue! @jpculp is taking a look at your PR. Meanwhile we will take a look at this with our security team and get back to you after completing the process.