Add generate_key function

README.md

@@ -14,11 +14,10 @@ gleam add casper@1
 
 ```gleam
 import casper
-import gleam/crypto
 
 pub fn main() -> Nil {
   // Generate a 32 byte encryption key
-  let key = crypto.strong_random_bytes(32)
+  let key = casper.generate_key()
 
   // This will fail if the key isn't the right size, i.e. 32 bytes
   let assert Ok(encrypted) = casper.encrypt(<<"casper">>, key)

src/casper.gleam

@@ -2,6 +2,11 @@
 //// libraries. The "with" variants allow you to add additional authenticated
 //// data AAD which is required for encryption and decryption.
 
+/// Generate 32 random bytes for use in the ChaCha20-Poly1305 cipher.
+@external(erlang, "casper_ffi", "generate_key")
+@external(javascript, "./casper_ffi.mjs", "generate_key")
+pub fn generate_key() -> BitArray
+
 @external(erlang, "casper_ffi", "encrypt_internal")
 @external(javascript, "./casper_ffi.mjs", "encrypt_internal")
 fn encrypt_internal(input: BitArray, key: BitArray) -> BitArray

src/casper_ffi.erl

@@ -1,12 +1,16 @@
 -module(casper_ffi).
 
 -export([
+    generate_key/0,
     encrypt_internal/2,
     decrypt_internal/2,
     encrypt_with_internal/3,
     decrypt_with_internal/3
 ]).
 
+generate_key() ->
+    crypto:strong_rand_bytes(32).
+
 encrypt_internal(Value, Key) ->
     Iv = crypto:strong_rand_bytes(12),
     {Encrypted, Tag} = crypto:crypto_one_time_aead(

src/casper_ffi.mjs

@@ -5,7 +5,11 @@ import * as crypto from "node:crypto";
 function strongRandomBytes(n) {
   return crypto.randomBytes(n);
 }
-
+
+export function generate_key() {
+  return new BitArray(crypto.randomBytes(32));
+}
+
 export function encrypt_internal(input, key) {
   const iv = strongRandomBytes(12);
   const cipher = crypto.createCipheriv('chacha20-poly1305', key.rawBuffer, iv);

test/casper_test.gleam

@@ -9,7 +9,7 @@ pub fn main() -> Nil {
 
 pub fn basic_roundtrip_no_associated_data_test() {
   let input = <<"casper test">>
-  let key = crypto.strong_random_bytes(32)
+  let key = casper.generate_key()
 
   let encrypted =
     casper.encrypt(input, key)
@@ -26,7 +26,7 @@ pub fn basic_roundtrip_no_associated_data_test() {
 pub fn basic_roundtrip_with_associated_data_test() {
   let input = <<"casper test">>
   let associated = <<"casper associated">>
-  let key = crypto.strong_random_bytes(32)
+  let key = casper.generate_key()
 
   let encrypted =
     casper.encrypt_with(input, associated, key)
@@ -43,7 +43,7 @@ pub fn basic_roundtrip_with_associated_data_test() {
 pub fn fails_when_decrypt_associated_data_differs_test() {
   let input = <<"casper test">>
   let associated = <<"casper associated">>
-  let key = crypto.strong_random_bytes(32)
+  let key = casper.generate_key()
 
   let encrypted =
     casper.encrypt_with(input, associated, key)