From 2.x.x

If you're on Lazysodium version 2 and you want to upgrade to version 3, then there are a few things that have been added which you need to note.

Key.java added

All cryptoSecretBoxKeygen functions now return a Key. A Key holds a bunch of bytes that represent maybe a master key, or a subkey, or any type of key. The reason why Lazysodium chose to use this was mainly because users of the library were getting confused as to what to put into functions like:

secretBoxLazy.cryptoSecretBoxEasy(String message, byte[] nonce, String key);

As you can see, the above function takes in a String key but does it take a hexadecimal key or a normal plain key? Users may want to input their own keys, or they may want to generate a key using cryptoSecretBoxKeygen. In the former scenario, the user may input something like "a_key_that_is_32_bytes" but the latter may generate something like "12ABEDAED21". The above function is actually expecting a hexadecimal string, so a user inputting "a_key_that_is_32_bytes" would generate something incorrect.

TL:DR

So as a result of number 1 above, we replaced the String key with an object Key. To create a Key object, you now are required to understand what the string is. You should choose one of the following:

// Choose this if the key is a hexadecimal string.
Key.fromHexString("12ABEDAED21");
​
// Choose this if the key is a plain string.
Key.fromPlainString("a_key_that_is_32_bytes");
​
// Choose this if the key in byte format
Key.fromBytes(bytes);