diff --git a/src/matrix/e2ee/ssss/common.js b/src/matrix/e2ee/ssss/common.js
new file mode 100644
index 00000000..6aab70d2
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+++ b/src/matrix/e2ee/ssss/common.js
@@ -0,0 +1,88 @@
+/*
+Copyright 2020 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.
+*/
+
+export class KeyDescription {
+    constructor(id, keyAccountData) {
+        this._id = id;
+        this._keyAccountData = keyAccountData;
+    }
+
+    get id() {
+        return this._id;
+    }
+
+    get passphraseParams() {
+        return this._keyAccountData?.content?.passphrase;
+    }
+
+    get algorithm() {
+        return this._keyAccountData?.content?.algorithm;
+    }
+}
+
+export class Key {
+    constructor(keyDescription, binaryKey) {
+        this._keyDescription = keyDescription;
+        this._binaryKey = binaryKey;
+    }
+
+    get id() {
+        return this._keyDescription.id;
+    }
+
+    get binaryKey() {
+        return this._binaryKey;
+    }
+
+    get algorithm() {
+        return this._keyDescription.algorithm;
+    }
+}
+
+export async function readDefaultKeyDescription(storage) {
+    const txn = await storage.readTxn([
+        storage.storeNames.accountData
+    ]);
+    const defaultKeyEvent = await txn.accountData.get("m.secret_storage.default_key");
+    const id = defaultKeyEvent?.content?.key;
+    if (!id) {
+        return;
+    }
+    const keyAccountData = await txn.accountData.get(`m.secret_storage.key.${id}`);
+    return new KeyDescription(id, keyAccountData);
+}
+
+export async function writeKey(storage, key) {
+    const txn = await storage.readWriteTxn([
+        storage.storeNames.session
+    ]);
+    try {
+        txn.session.set("ssssKey", {id: key.id, binaryKey: key.binaryKey});
+    } catch (err) {
+        txn.abort();
+        throw err;
+    }
+    await txn.complete();
+}
+
+export async function readKey(txn) {
+    const key = await txn.session.get("ssssKey");
+    if (!key) {
+        return;
+    }
+    const keyAccountData = await txn.accountData.get(`m.secret_storage.key.${key.id}`);
+    return new Key(new KeyDescription(key.id, keyAccountData), key.binaryKey);
+}