diff --git a/analysis_options.yaml b/analysis_options.yaml
index fff9bb4..f7c7e75 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1,14 +1,9 @@
-analyzer:
-  strong-mode: true
-
 linter:
   rules:
     - camel_case_types
     - empty_constructor_bodies
     - always_declare_return_types
-    - camel_case_types
     - constant_identifier_names
-    - empty_constructor_bodies
     - implementation_imports
     - library_names
     - library_prefixes
@@ -18,7 +13,6 @@ linter:
     - package_prefixed_library_names
     - prefer_is_not_empty
     - slash_for_doc_comments
-    - super_goes_last
     - type_annotate_public_apis
     - type_init_formals
     - unnecessary_getters_setters
@@ -34,14 +28,12 @@ linter:
     - iterable_contains_unrelated_type
     - list_remove_unrelated_type
     - test_types_in_equals
-    - throw_in_finally
     - valid_regexps
     - annotate_overrides
     - avoid_init_to_null
     - avoid_return_types_on_setters
     - await_only_futures
     - empty_catches
-    - prefer_is_not_empty
     - sort_constructors_first
     - sort_unnamed_constructors_first
     - unawaited_futures
diff --git a/lib/pbkdf2.dart b/lib/pbkdf2.dart
index 24e40ca..1e45694 100644
--- a/lib/pbkdf2.dart
+++ b/lib/pbkdf2.dart
@@ -13,18 +13,18 @@ class PBKDF2 {
   /// Creates instance capable of generating a key.
   ///
   /// [hashAlgorithm] defaults to [sha256].
-  PBKDF2({Hash hashAlgorithm}) {
+  PBKDF2({Hash? hashAlgorithm}) {
     this.hashAlgorithm = hashAlgorithm ?? sha256;
   }
 
-  Hash get hashAlgorithm => _hashAlgorithm;
-  set hashAlgorithm(Hash algorithm) {
+  Hash? get hashAlgorithm => _hashAlgorithm;
+  set hashAlgorithm(Hash? algorithm) {
     _hashAlgorithm = algorithm;
-    _blockSize = _hashAlgorithm.convert([1, 2, 3]).bytes.length;
+    _blockSize = _hashAlgorithm!.convert([1, 2, 3]).bytes.length;
   }
 
-  Hash _hashAlgorithm;
-  int _blockSize;
+  Hash? _hashAlgorithm;
+  late int _blockSize;
 
   /// Hashes a [password] with a given [salt].
   ///
@@ -40,7 +40,7 @@ class PBKDF2 {
     }
 
     var numberOfBlocks = (keyLength / _blockSize).ceil();
-    var hmac = new Hmac(hashAlgorithm, utf8.encode(password));
+    var hmac = new Hmac(hashAlgorithm!, utf8.encode(password));
     var key = new ByteData(keyLength);
     var offset = 0;
 
@@ -90,7 +90,7 @@ class PBKDF2Exception implements Exception {
 
 class _XORDigestSink extends Sink<Digest> {
   _XORDigestSink(ByteData inputBuffer, Hmac hmac) {
-    lastDigest = hmac.convert(inputBuffer.buffer.asUint8List()).bytes;
+    lastDigest = hmac.convert(inputBuffer.buffer.asUint8List()).bytes as Uint8List;
     bytes = new ByteData(lastDigest.length)
       ..buffer.asUint8List().setRange(0, lastDigest.length, lastDigest);
   }
@@ -109,12 +109,12 @@ class _XORDigestSink extends Sink<Digest> {
     return hashSink.bytes.buffer.asUint8List();
   }
 
-  ByteData bytes;
-  Uint8List lastDigest;
+  late ByteData bytes;
+  late Uint8List lastDigest;
 
   @override
   void add(Digest digest) {
-    lastDigest = digest.bytes;
+    lastDigest = digest.bytes as Uint8List;
     for (var i = 0; i < digest.bytes.length; i++) {
       bytes.setUint8(i, bytes.getUint8(i) ^ lastDigest[i]);
     }
diff --git a/pubspec.yaml b/pubspec.yaml
index ba6692e..b523b31 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,10 +5,10 @@ homepage: https://github.com/stablekernel/dart-password-hash
 description: PBKDF2 password hashing utility
 
 environment:
-  sdk: ">=2.0.0 <3.0.0"
+  sdk: '>=2.12.0-133.7.beta <3.0.0'
 
 dependencies:
-  crypto: ^2.0.0
+  crypto: ^3.0.0
 
 dev_dependencies:
   test: ^1.3.0