diff --git a/tool/cms_bench.dart b/tool/cms_bench.dart
new file mode 100644
index 0000000..5a0eacf
--- /dev/null
+++ b/tool/cms_bench.dart
@@ -0,0 +1,120 @@
+// Times the CMS reader of datekeys-dart, stage 5a, on the VM and compiled
+// to JavaScript: the verification of one ECDSA signature on each curve and
+// of one RSA signature of each size and scheme, the reading of a
+// certificate, and a whole signature and a whole token read and checked. It
+// reads no file: the cases are those of test/vectors/cms_vectors.g.dart.
+//
+//   dart run tool/cms_bench.dart
+//
+//   dart compile js -O2 -o cms_bench.js tool/cms_bench.dart
+//   node cms_bench.js
+//
+// ignore_for_file: avoid_print
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:datekeys/src/bytes.dart';
+import 'package:datekeys/src/cms.dart';
+import 'package:datekeys/src/ecdsa.dart';
+import 'package:datekeys/src/nist_curves.dart';
+import 'package:datekeys/src/rsa.dart';
+
+import '../test/vectors/cms_vectors.g.dart';
+
+typedef Json = Map<String, Object?>;
+
+List<Json> _cases(String json, String section) =>
+    ((jsonDecode(json) as Json)[section]! as List).cast<Json>();
+
+Json _named(String json, String section, String name) =>
+    _cases(json, section).firstWhere((c) => c['name'] == name);
+
+Uint8List _hex(Object? v) => fromHex(v! as String);
+
+/// The mean time of [f] in milliseconds, over at least [minRuns] runs and
+/// about [budgetMs] milliseconds, after one run to warm up.
+double time(void Function() f, {int minRuns = 3, int budgetMs = 2000}) {
+  f();
+  final sw = Stopwatch()..start();
+  var runs = 0;
+  while (runs < minRuns || sw.elapsedMilliseconds < budgetMs) {
+    f();
+    runs++;
+  }
+  return sw.elapsedMicroseconds / 1000 / runs;
+}
+
+String ms(double v) => '${v.toStringAsFixed(v < 10 ? 2 : 0)} ms';
+
+void main() {
+  final curves = {'P-256': p256, 'P-384': p384, 'P-521': p521};
+  final keys = _cases(cmsEcdsaJson, 'keys');
+  for (final (curve, hash) in const [
+    ('P-256', 'SHA-256'),
+    ('P-384', 'SHA-384'),
+    ('P-521', 'SHA-512'),
+  ]) {
+    final c = _cases(cmsEcdsaJson, 'verify').firstWhere(
+      (c) => (c['name']! as String).startsWith('$curve, valid over $hash, '),
+    );
+    final k = keys[c['key']! as int];
+    final point = decodeUncompressed(curves[curve]!, _hex(k['point']))!;
+    final h = _hex(c['hash']);
+    final sig = _hex(c['sig']);
+    if (!verifyEcdsaAsn1(point, h, sig)) throw StateError('not valid');
+    print(
+      'ECDSA $curve, $hash, one verification: '
+      '${ms(time(() => verifyEcdsaAsn1(point, h, sig)))}',
+    );
+  }
+
+  final rsaKeys = _cases(cmsRsaJson, 'keys');
+  for (final c in _cases(cmsRsaJson, 'valid')) {
+    final k = rsaKeys[c['key']! as int];
+    if (k['e'] != 65537) continue;
+    final key = RsaPublicKey(
+      BigInt.parse(k['n']! as String, radix: 16),
+      k['e']! as int,
+    );
+    final digest = _hex(c['digest']);
+    final sig = _hex(c['sig']);
+    bool verify() => c['scheme'] == 'pss'
+        ? verifyPss(key, Sha2.sha256, digest, sig)
+        : verifyPkcs1v15(key, Sha2.sha256, digest, sig);
+    if (!verify()) throw StateError('not valid');
+    print('RSA ${c['name']}, one verification: ${ms(time(verify))}');
+  }
+
+  for (final name in const ['field by field', 'rsa']) {
+    final der = _hex(_named(cmsCertsJson, 'bases', name)['der']);
+    print(
+      'parseCert, the certificate "$name" (${der.length} bytes): '
+      '${ms(time(() => parseCert(der).holder))}',
+    );
+  }
+
+  final message = _hex((jsonDecode(cmsMutationsJson) as Json)['message']);
+  for (final name in const ['sealed', 'co-signature']) {
+    final der = _hex(_named(cmsMutationsJson, 'signature_bases', name)['der']);
+    void check() {
+      for (final s in parseSignature(der).signers) {
+        if (s.check(message) != CmsResult.valid) throw StateError('invalid');
+      }
+    }
+
+    print(
+      'parseSignature and check, "$name" (${der.length} bytes): '
+      '${ms(time(check))}',
+    );
+  }
+  final subject = _hex((jsonDecode(cmsMutationsJson) as Json)['subject']);
+  final token = _hex(_named(cmsMutationsJson, 'token_bases', 'ecdsa')['der']);
+  void checkToken() {
+    if (!parseToken(token).check(subject)) throw StateError('invalid');
+  }
+
+  print(
+    'parseToken and check, ECDSA P-256 (${token.length} bytes): '
+    '${ms(time(checkToken))}',
+  );
+}