diff --git a/libraries/deno-commons-mod.ts b/libraries/deno-commons-mod.ts
index 125053f..d54a660 100644
--- a/libraries/deno-commons-mod.ts
+++ b/libraries/deno-commons-mod.ts
@@ -9,6 +9,7 @@ import {spawn, SpawnOptionsWithoutStdio} from "node:child_process";
 import {createWriteStream, mkdir, readFile, readFileSync, rm, stat, writeFile,} from "node:fs";
 import {pipeline} from "node:stream";
 import {promisify} from "node:util";
+import {getRandomValues} from "node:crypto";
 
 // reference: https://docs.deno.com/examples/hex_base64_encoding/
 // import { decodeBase64, encodeBase64 } from "jsr:@std/encoding/base64";
@@ -996,6 +997,104 @@ export function encodeBase64Url(
     );
 }
 
+export function random(length: number): ArrayBufferLike {
+    const buffer = new Uint8Array(length);
+    getRandomValues(buffer);
+    return buffer;
+}
+
+let __masterEncryptionKey1 = null;
+let __masterEncryptionKey2 = null;
+async function __getMasterEncryptionKey1(): Promise<string> {
+    if (!__masterEncryptionKey1) {
+        const service = "deno-commons-mode";
+        const user = "master-encryption-key-1";
+        __masterEncryptionKey1 = await getKeyRingPassword(service, user);
+        if (!__masterEncryptionKey1) {
+            __masterEncryptionKey1 = encodeBase64(random(1024));
+            await setKeyRingPassword(service, user, __masterEncryptionKey1);
+        }
+    }
+    return __masterEncryptionKey1;
+}
+
+async function __getMasterEncryptionKey2(): Promise<string> {
+    if (!__masterEncryptionKey2) {
+        const filename = "~/.deno-common-mod-master-encryption-key-2";
+        __masterEncryptionKey2 = await readFileToString(filename);
+        if (!__masterEncryptionKey2) {
+            __masterEncryptionKey2 = encodeBase64(random(4096));
+            await writeStringToFile(filename, __masterEncryptionKey2);
+        }
+    }
+    return __masterEncryptionKey2;
+}
+
+let __masterEncryptionKey = null;
+async function __getMasterEncryptionKey(): Promise<CryptoKey> {
+    if (!__masterEncryptionKey) {
+        const key1 = await __getMasterEncryptionKey1();
+        const key2 = await __getMasterEncryptionKey2();
+        __masterEncryptionKey = await sha256OfString(
+            "master-encryption-key-prefix:" + key1 + ":" + key2,
+        );
+    }
+    return await crypto.subtle.importKey(
+        "raw",
+        __masterEncryptionKey,
+        "AES-GCM",
+        false,
+        ["encrypt", "decrypt"],
+    );
+}
+
+export async function encryptDefault(
+    plaintext: string | BufferSource,
+): Promise<ArrayBuffer> {
+    const input = typeof plaintext === "string"
+        ? new TextEncoder().encode(plaintext)
+        : plaintext;
+    const key = await __getMasterEncryptionKey();
+    const nonce = await random(12);
+    const ciphertext = await crypto.subtle.encrypt(
+        { name: "AES-GCM", iv: nonce },
+        key,
+        input,
+    );
+    const blob = new Blob([nonce, ciphertext]);
+    return await blob.arrayBuffer();
+}
+
+export async function encryptDefaultAsBase64(
+    plaintext: string | BufferSource,
+): Promise<ArrayBuffer> {
+    return encodeBase64(await encryptDefault(plaintext));
+}
+
+export async function decryptDefault(
+    ciphertext: string | BufferSource,
+): Promise<ArrayBuffer> {
+    const input = typeof ciphertext === "string"
+        ? decodeBase64(ciphertext)
+        : ciphertext;
+    const key = await __getMasterEncryptionKey();
+    const nonce = input.slice(0, 12);
+    const ciphertextWithTag = input.slice(12);
+    const plaintext = await crypto.subtle.decrypt(
+        { name: "AES-GCM", iv: nonce },
+        key,
+        ciphertextWithTag,
+    );
+    return plaintext;
+}
+
+export async function decryptDefaultAsString(
+    ciphertext: string | BufferSource,
+): Promise<string> {
+    const plaintext = await decryptDefault(ciphertext);
+    return new TextDecoder().decode(plaintext);
+}
+
 export async function getKeyRingPassword(
     service: string,
     user: string,
@@ -1012,7 +1111,7 @@ export async function getKeyRingPassword(
             return null;
         }
         throw new Error(
-            `keyring.rs -g failed, code: ${code}, stdout: ${stdoutString}, stderr: ${stderrString}`,
+            `keyring.rs -g failed, code: ${processOutput.code}, stdout: ${stdoutString}, stderr: ${stderrString}`,
         );
     }
     const result = JSON.parse(stdoutString) as {
@@ -1035,7 +1134,7 @@ export async function setKeyRingPassword(
     const stderrString = processOutput.getStderrAsStringThenTrim();
     if (processOutput.code != 0) {
         throw new Error(
-            `keyring.rs -s failed, code: ${code}, stdout: ${stdoutString}, stderr: ${stderrString}`,
+            `keyring.rs -s failed, code: ${processOutput.code}, stdout: ${stdoutString}, stderr: ${stderrString}`,
         );
     }
     return;