rust backup restore support (#3709)

* Refactor key backup recovery to prepare for rust

* rust backup restore support

* Move export out of old crypto to api with re-export

* extract base64 utility

* add tests for base64 util

* more efficient regex

* fix typo

spec/unit/crypto/base64.spec.ts

@@ -0,0 +1,52 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { TextEncoder, TextDecoder } from "util";
+
+import { decodeBase64, encodeBase64, encodeUnpaddedBase64 } from "../../../src/common-crypto/base64";
+
+describe("Crypto Base64 encoding", () => {
+    it("Should decode properly encoded data", async () => {
+        const toEncode = "encoding hello world";
+        const encoded = encodeBase64(new TextEncoder().encode(toEncode));
+        const decoded = new TextDecoder().decode(decodeBase64(encoded));
+
+        expect(decoded).toStrictEqual(toEncode);
+    });
+
+    it("Encode unpadded should not have padding", async () => {
+        const toEncode = "encoding hello world";
+        const data = new TextEncoder().encode(toEncode);
+
+        const paddedEncoded = encodeBase64(data);
+        const unpaddedEncoded = encodeUnpaddedBase64(data);
+
+        expect(paddedEncoded).not.toEqual(unpaddedEncoded);
+
+        const padding = paddedEncoded.charAt(paddedEncoded.length - 1);
+        expect(padding).toStrictEqual("=");
+    });
+
+    it("Decode should be indifferent to padding", async () => {
+        const withPadding = "ZW5jb2RpbmcgaGVsbG8gd29ybGQ=";
+        const withoutPadding = "ZW5jb2RpbmcgaGVsbG8gd29ybGQ";
+
+        const decodedPad = decodeBase64(withPadding);
+        const decodedNoPad = decodeBase64(withoutPadding);
+
+        expect(decodedPad).toStrictEqual(decodedNoPad);
+    });
+});