Create xchacha20NonceLength constant

packages/crypto/src/index.ts

@@ -9,6 +9,7 @@ export {
   Xchacha20poly1305IetfKey,
   Xchacha20poly1305IetfMessage,
   Xchacha20poly1305IetfNonce,
+  xchacha20NonceLength,
   Argon2id,
   Argon2idOptions,
   Ed25519,

packages/crypto/src/libsodium.ts

@@ -91,6 +91,13 @@ export class Ed25519 {
   }
 }
 
+/**
+ * Nonce length in bytes for all flavours of XChaCha20.
+ *
+ * @see https://libsodium.gitbook.io/doc/advanced/stream_ciphers/xchacha20#notes
+ */
+export const xchacha20NonceLength = 24;
+
 export class Xchacha20poly1305Ietf {
   public static async encrypt(
     message: Xchacha20poly1305IetfMessage,