This change adds the equivalents of crypto_sign, crypto_sign_open and crypto_sign_keypair in TweetNaCl and libsodium using the Ed25519 system. The original NaCl codebase does not contain functions with identical semantics but its documentation stated the intent of using Ed25519 in future releases. Fixes golang/go#24350 Change-Id: I4c3c86b4875f2f718ad9299c2274b4ad9e11fbeb Reviewed-on: https://go-review.googlesource.com/100578 Run-TryBot: Adam Langley <agl@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Adam Langley <agl@golang.org>