Add dependency on libsodium

pubspec.lock

@@ -218,6 +218,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.0"
+  ffi:
+    dependency: transitive
+    description:
+      name: ffi
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.1.3"
   file:
     dependency: transitive
     description:
@@ -279,6 +286,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "3.3.3"
+  flutter_sodium:
+    dependency: "direct main"
+    description:
+      name: flutter_sodium
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.1.4"
   flutter_svg:
     dependency: "direct main"
     description:

pubspec.yaml

@@ -66,6 +66,7 @@ dependencies:
   crisp: ^0.1.3
   uuid: 2.2.2
   steel_crypt: ^2.2.2+1
+  flutter_sodium: ^0.1.4
 
 dev_dependencies:
   flutter_test: