NaCl: add default parameter for optional random generated sk

[anonimal]

This is useful for implementations who can't afford to clobber the
existing sk buffer or who are limited by their existing interface
(e.g., they must re-use the privkey).

This is needed for monero-project/kovri#909.

@noloader I know, altering the interface is heresy. I welcome your feedback.

[anonimal]

ping @noloader

[noloader]

@anonimal,

Sorry about the late reply here.

We added a new functions called crypto_sign_sk2pk. It should accomplish what you need without changing the API. Doxygen docs at crypto_sign_sk2pk(). The important part is:

crypto_sign_sk2pk() creates an ed25519 public key from an existing 32-byte secret key. The function does not backfill the tail bytes of the secret key with the calculated public key.

That means the check-in differs from the pull request by not back-filling the public key into the tail of the secret key. If you want the public key concatenated with the secret key then perform a memcpy after crypto_sign_sk2pk(). It also means your sk buffer must be at least 64-bytes in size (which I was not clear if it was the case).

Also see Commit d8946df8eb34 and Kovri | PR 909.

[anonimal]

Thank you so much @noloader !

Very important note: this is not for the Java I2P library as noted in Doxygen. This is entirely a Kovri request, and kovri has no java I2P interoperability (as in, we don't use their libraries in any way). They also do not use crypto++ in any way. We are also not associated with their project in any way outside of the open specifications that they provide.

Should I open a pull request?

[anonimal]

Sorry, we're nearing a release so my stress level is to the max and I overlooked what you meant.

no java I2P interoperability

We are interoperable, but I think it's important to note that this is a specification requirement and not a library one because A) we may continue to use this function if/when we don't use I2P (or choose not to interop with Java I2P) and B) because the function itself is a cool tool which, IMHO, can also be applied elsewhere.