DeriveECDHX25519 does X25519 ECDH using fromPrivKey and toPubKey.

LengthPrefix array with a bigEndian uint32 value of array's length.

Nonce makes a nonce using blake2b, to match the format expected by libsodium.

PublicEd25519toCurve25519 takes an Ed25519 public key and provides the corresponding Curve25519 public key This function wraps PublicKeyToCurve25519 from Adam Langley's ed25519 repo: https://github.com/agl/ed25519 now moved to https://github.com/teserakt-io/golang-ed25519.

SecretEd25519toCurve25519 converts a secret key from Ed25519 to curve25519 format This function wraps PrivateKeyToCurve25519 from Adam Langley's ed25519 repo: https://github.com/agl/ed25519 now moved to https://github.com/teserakt-io/golang-ed25519.

Curve25519KeySize number of bytes in a Curve25519 public or private key.

NonceSize size of a nonce used by Box encryption (Xchacha20Poly1305).