Comment by Sjoerd

When doing symmetric encryption you usually need a nonce or IV, which is also sent to the other party along with the ciphertext and authentication tag. Why does the API for libsodium allow you to specify your own nonce and keeps it separate from the ciphertext? The function crypto_secretbox_easy includes the authentication tag in the ciphertext, but you still have to provide the nonce yourself and it is not included in the ciphertext. Wouldn't it be easier still if the nonce was generated within this function and also added to the ciphertext?