Make PrecomputedValues public

[BrettMayson]

I need access to these values in order to store a custom private key format, this is preventing me from switching away from openssl

[tarcieri]

Is there a particular reason why you want to store these values instead of computing them on-the-fly?

The trend in RSA private key format design has been to store fewer precomputed values rather than more. Modern key formats store only d and can compute everything else from that and the public key.

Also: are you actually using multiprime RSA? (re: crt_values)

[BrettMayson]

I need to store a custom format that I have no control over, which requires these values to be stored

[tarcieri]

Do you actually need to support multiprime RSA?

It would probably be worth keeping that out of the public API, especially as it currently has an odd definition owing to PKCS#1 also needing the CRT coefficient for two primes, so the current vector stores "additional CRT coefficients" beyond that one IIUC.

[newpavlov]

I don't think we should make the fields public. If you only need to read pre-computed values, then a bunch of getters should do the job. If you need to restore the values from serialized data, then we would need to think about validation.

[BrettMayson]

Also: are you actually using multiprime RSA? (re: crt_values)

No, just dp, dq and qinv

I can modify this PR to have getters for those 3 values in a few days

[tarcieri]

In that case it sounds like you should just add read-only getter methods for those three