diff --git a/README.md b/README.md
index 2a28bb0..f85f318 100644
--- a/README.md
+++ b/README.md
@@ -48,22 +48,18 @@ separate output directories.
 src/
   background/       — service worker / background script
     index.js        — extension lifecycle, message routing
-    wallet.js       — wallet management (create, import, derive)
+    wallet.js       — wallet management (create, import, derive via ethers.js)
     provider.js     — EIP-1193 JSON-RPC provider implementation
-    transaction.js  — transaction construction and signing
   popup/            — popup UI (the main wallet interface)
     index.html
     index.js
-    components/     — UI components (account list, send form, etc.)
     styles/         — CSS (Tailwind)
   content/          — content script injected into web pages
     index.js        — injects the provider into page context
     inpage.js       — the window.ethereum provider object
   shared/           — shared utilities
-    crypto.js       — BIP-39 mnemonic, HD key derivation, signing
-    storage.js      — encrypted storage abstraction
+    vault.js        — encrypted storage via libsodium
     constants.js    — chain IDs, default RPC endpoints, ERC-20 ABI
-    rpc.js          — JSON-RPC client for Ethereum nodes
 manifest/
   chrome.json       — Manifest V3 for Chrome
   firefox.json      — Manifest V2/V3 for Firefox
@@ -197,32 +193,75 @@ What the extension does NOT do:
 The user's RPC endpoint is the single point of external communication. Users who
 want maximum privacy can point it at their own Ethereum node.
 
+### Dependencies
+
+AutistMask uses two runtime libraries. All cryptographic operations are
+delegated to these libraries — see the Crypto Policy section below.
+
+| Package                   | Version | License | Purpose                                                                                                                                                                                                                                                 |
+| ------------------------- | ------- | ------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `ethers`                  | 6.16.0  | MIT     | All Ethereum operations: BIP-39 mnemonic generation/validation, BIP-32/BIP-44 HD key derivation (`m/44'/60'/0'/0/n`), secp256k1 signing, transaction construction, ERC-20 contract interaction, JSON-RPC communication, address derivation (keccak256). |
+| `libsodium-wrappers-sumo` | 0.8.2   | ISC     | Password-based encryption of secrets at rest: Argon2id key derivation (`crypto_pwhash`), authenticated encryption (`crypto_secretbox` / XSalsa20-Poly1305).                                                                                             |
+
+Dev dependencies (not shipped in extension):
+
+| Package            | Version | License | Purpose         |
+| ------------------ | ------- | ------- | --------------- |
+| `tailwindcss`      | 4.2.1   | MIT     | CSS compilation |
+| `@tailwindcss/cli` | 4.2.1   | MIT     | Tailwind CLI    |
+| `jest`             | 30.2.0  | MIT     | Test runner     |
+| `prettier`         | 3.8.1   | MIT     | Code formatter  |
+
+### Crypto Policy
+
+**No raw crypto primitives in application code.** If the strings `aes`, `sha`,
+`pbkdf`, `hmac`, `encrypt`, `decrypt`, `hash`, `cipher`, `digest`, `sign`
+(case-insensitive) appear in our own source code (outside of `node_modules/`),
+it is almost certainly a bug. All cryptographic operations must go through
+`ethers` or `libsodium-wrappers-sumo`. This policy exists because:
+
+- Rolling your own crypto is the single most common source of security
+  vulnerabilities in wallet software.
+- Both libraries are widely audited and battle-tested.
+- Keeping crypto out of application code makes security review tractable:
+  reviewers only need to verify that we call the libraries correctly, not that
+  we implemented crypto correctly.
+
+Exceptions require explicit authorization in a code comment referencing this
+policy.
+
 ### Key Decisions
 
 - **No framework**: The popup UI is vanilla JS and HTML. The extension is small
   enough that a framework adds unnecessary complexity and attack surface.
 - **Encrypted storage**: Recovery phrases and private keys are encrypted at rest
-  in the extension's local storage. The encryption scheme:
-    - The user's password is run through PBKDF2-SHA256 (600,000 iterations) with
-      a random salt to derive a 256-bit encryption key.
-    - The encryption key + a random IV encrypt the secret material using
-      AES-256-GCM.
-    - Stored blob: `{ salt, iv, ciphertext, authTag }`.
+  in the extension's local storage using libsodium. The encryption scheme:
+    - The user's password is run through Argon2id (`crypto_pwhash`) to derive a
+      256-bit encryption key. Argon2id is memory-hard, making GPU/ASIC brute
+      force attacks expensive.
+    - The derived key encrypts the secret material using XSalsa20-Poly1305
+      (`crypto_secretbox`), which provides authenticated encryption (the
+      ciphertext cannot be tampered with without detection).
+    - Stored blob: `{ salt, nonce, ciphertext }` (the auth tag is part of the
+      `crypto_secretbox` output).
     - **The password is NOT used in address derivation.** It exists solely to
       protect the recovery phrase / private key on disk. Anyone with the
       recovery phrase can restore the wallet on any device without this
       password. This matches MetaMask's behavior.
-- **BIP-39 / BIP-44**: Standard mnemonic generation and HD key derivation
-  (`m/44'/60'/0'/0/n`) for Ethereum address compatibility. The BIP-39 passphrase
-  is always empty (matching MetaMask and most wallet software). The user's
-  password is completely separate and has no effect on which addresses are
-  generated.
+- **BIP-39 / BIP-44 via ethers.js**: Mnemonic generation, validation, and HD key
+  derivation (`m/44'/60'/0'/0/n`) are handled entirely by ethers.js. The BIP-39
+  passphrase is always empty (matching MetaMask and most wallet software). The
+  user's password is completely separate and has no effect on which addresses
+  are generated.
+- **ethers.js for everything Ethereum**: Transaction construction, signing, gas
+  estimation, RPC communication, ERC-20 contract calls, and address derivation
+  are all handled by ethers.js. This means zero hand-rolled Ethereum logic.
 - **EIP-1193 provider**: The content script injects a `window.ethereum` object
   that implements the EIP-1193 provider interface, enabling web3 site
   connectivity.
-- **Minimal RPC**: The extension communicates with Ethereum nodes via JSON-RPC.
-  The default endpoint is configurable. No Infura dependency — users can point
-  it at any Ethereum JSON-RPC endpoint.
+- **Minimal RPC**: The extension communicates with Ethereum nodes via JSON-RPC
+  through ethers.js's `JsonRpcProvider`. The default endpoint is configurable.
+  No Infura dependency — users can point it at any Ethereum JSON-RPC endpoint.
 
 ### Supported Functionality
 
diff --git a/package.json b/package.json
index ba677ea..ec311d3 100644
--- a/package.json
+++ b/package.json
@@ -18,5 +18,8 @@
         "prettier": "^3.8.1",
         "tailwindcss": "^4.2.1"
     },
-    "dependencies": {}
+    "dependencies": {
+        "ethers": "^6.16.0",
+        "libsodium-wrappers-sumo": "^0.8.2"
+    }
 }
diff --git a/yarn.lock b/yarn.lock
index 99e8bf5..d1d018f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2,6 +2,11 @@
 # yarn lockfile v1
 
 
+"@adraffy/ens-normalize@1.10.1":
+  version "1.10.1"
+  resolved "https://registry.yarnpkg.com/@adraffy/ens-normalize/-/ens-normalize-1.10.1.tgz#63430d04bd8c5e74f8d7d049338f1cd9d4f02069"
+  integrity sha512-96Z2IP3mYmF1Xg2cDm8f1gWGf/HUVedQ3FMifV4kG/PQ4yEP51xDtRAEfhVNt5f/uzpNkZHwWQuUcu6D6K+Ekw==
+
 "@babel/code-frame@^7.0.0", "@babel/code-frame@^7.27.1", "@babel/code-frame@^7.28.6", "@babel/code-frame@^7.29.0":
   version "7.29.0"
   resolved "https://registry.yarnpkg.com/@babel/code-frame/-/code-frame-7.29.0.tgz#7cd7a59f15b3cc0dcd803038f7792712a7d0b15c"
@@ -592,6 +597,18 @@
     "@emnapi/runtime" "^1.7.1"
     "@tybys/wasm-util" "^0.10.1"
 
+"@noble/curves@1.2.0":
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/@noble/curves/-/curves-1.2.0.tgz#92d7e12e4e49b23105a2555c6984d41733d65c35"
+  integrity sha512-oYclrNgRaM9SsBUBVbb8M6DTV7ZHRTKugureoYEncY5c65HOmRzvSiTE3y5CYaPYJA/GVkrhXEoF0M3Ya9PMnw==
+  dependencies:
+    "@noble/hashes" "1.3.2"
+
+"@noble/hashes@1.3.2":
+  version "1.3.2"
+  resolved "https://registry.yarnpkg.com/@noble/hashes/-/hashes-1.3.2.tgz#6f26dbc8fbc7205873ce3cee2f690eba0d421b39"
+  integrity sha512-MVC8EAQp7MvEcm30KWENFjgR+Mkmf+D189XJTkFIlwohU5hcBbn1ZkKq7KVTi2Hme3PMGF390DaL52beVrIihQ==
+
 "@parcel/watcher-android-arm64@2.5.6":
   version "2.5.6"
   resolved "https://registry.yarnpkg.com/@parcel/watcher-android-arm64/-/watcher-android-arm64-2.5.6.tgz#5f32e0dba356f4ac9a11068d2a5c134ca3ba6564"
@@ -887,6 +904,13 @@
   dependencies:
     undici-types "~7.18.0"
 
+"@types/node@22.7.5":
+  version "22.7.5"
+  resolved "https://registry.yarnpkg.com/@types/node/-/node-22.7.5.tgz#cfde981727a7ab3611a481510b473ae54442b92b"
+  integrity sha512-jML7s2NAzMWc//QSJ1a3prpk78cOPchGvXJsC3C6R6PSMoooztvRVQEz89gmBTBY1SPMaqo5teB4uNHPdetShQ==
+  dependencies:
+    undici-types "~6.19.2"
+
 "@types/stack-utils@^2.0.3":
   version "2.0.3"
   resolved "https://registry.yarnpkg.com/@types/stack-utils/-/stack-utils-2.0.3.tgz#6209321eb2c1712a7e7466422b8cb1fc0d9dd5d8"
@@ -1006,6 +1030,11 @@
   resolved "https://registry.yarnpkg.com/@unrs/resolver-binding-win32-x64-msvc/-/resolver-binding-win32-x64-msvc-1.11.1.tgz#538b1e103bf8d9864e7b85cc96fa8d6fb6c40777"
   integrity sha512-lrW200hZdbfRtztbygyaq/6jP6AKE8qQN2KvPcJ+x7wiD038YtnYtZ82IMNJ69GJibV7bwL3y9FgK+5w/pYt6g==
 
+aes-js@4.0.0-beta.5:
+  version "4.0.0-beta.5"
+  resolved "https://registry.yarnpkg.com/aes-js/-/aes-js-4.0.0-beta.5.tgz#8d2452c52adedebc3a3e28465d858c11ca315873"
+  integrity sha512-G965FqalsNyrPqgEGON7nIx1e/OVENSgiEIzyC63haUMuvNnwIgIjMs52hlTCKhkBny7A2ORNlfY9Zu+jmGk1Q==
+
 ansi-escapes@^4.3.2:
   version "4.3.2"
   resolved "https://registry.yarnpkg.com/ansi-escapes/-/ansi-escapes-4.3.2.tgz#6b2291d1db7d98b6521d5f1efa42d0f3a9feb65e"
@@ -1350,6 +1379,19 @@ esprima@^4.0.0:
   resolved "https://registry.yarnpkg.com/esprima/-/esprima-4.0.1.tgz#13b04cdb3e6c5d19df91ab6987a8695619b0aa71"
   integrity sha512-eGuFFw7Upda+g4p+QHvnW0RyTX/SVeJBDM/gCtMARO0cLuT2HcEKnTPvhjV6aGeqrCB/sbNop0Kszm0jsaWU4A==
 
+ethers@^6.16.0:
+  version "6.16.0"
+  resolved "https://registry.yarnpkg.com/ethers/-/ethers-6.16.0.tgz#fff9b4f05d7a359c774ad6e91085a800f7fccf65"
+  integrity sha512-U1wulmetNymijEhpSEQ7Ct/P/Jw9/e7R1j5XIbPRydgV2DjLVMsULDlNksq3RQnFgKoLlZf88ijYtWEXcPa07A==
+  dependencies:
+    "@adraffy/ens-normalize" "1.10.1"
+    "@noble/curves" "1.2.0"
+    "@noble/hashes" "1.3.2"
+    "@types/node" "22.7.5"
+    aes-js "4.0.0-beta.5"
+    tslib "2.7.0"
+    ws "8.17.1"
+
 execa@^5.1.1:
   version "5.1.1"
   resolved "https://registry.yarnpkg.com/execa/-/execa-5.1.1.tgz#f80ad9cbf4298f7bd1d4c9555c21e93741c411dd"
@@ -2004,6 +2046,18 @@ leven@^3.1.0:
   resolved "https://registry.yarnpkg.com/leven/-/leven-3.1.0.tgz#77891de834064cccba82ae7842bb6b14a13ed7f2"
   integrity sha512-qsda+H8jTaUaN/x5vzW2rzc+8Rw4TAQ/4KjB46IwK5VH+IlVeeeje/EoZRpiXvIqjFgK84QffqPztGI3VBLG1A==
 
+libsodium-sumo@^0.8.0:
+  version "0.8.2"
+  resolved "https://registry.yarnpkg.com/libsodium-sumo/-/libsodium-sumo-0.8.2.tgz#6aee0ce5d5f850341327a2990531a71319d86c62"
+  integrity sha512-uMgnjphJ717jLN+jFG1HUgNrK/gOVVfaO1DGZ1Ig/fKLKLVhvaH/sM1I1v784JFvmkJDaczDpi7xSYC4Jvdo1Q==
+
+libsodium-wrappers-sumo@^0.8.2:
+  version "0.8.2"
+  resolved "https://registry.yarnpkg.com/libsodium-wrappers-sumo/-/libsodium-wrappers-sumo-0.8.2.tgz#3bc6ef80070d531622ccd41a317b61d32a78a7f2"
+  integrity sha512-wd1xAY++Kr6VMikSaa4EPRAHJmFvNlGWiiwU3Jh3GR1zRYF3/I3vy/wYsr4k3LVsNzwb9sqfEQ4LdVQ6zEebyQ==
+  dependencies:
+    libsodium-sumo "^0.8.0"
+
 lightningcss-android-arm64@1.31.1:
   version "1.31.1"
   resolved "https://registry.yarnpkg.com/lightningcss-android-arm64/-/lightningcss-android-arm64-1.31.1.tgz#609ff48332adff452a8157a7c2842fd692a8eac4"
@@ -2543,6 +2597,11 @@ to-regex-range@^5.0.1:
   dependencies:
     is-number "^7.0.0"
 
+tslib@2.7.0:
+  version "2.7.0"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-2.7.0.tgz#d9b40c5c40ab59e8738f297df3087bf1a2690c01"
+  integrity sha512-gLXCKdN1/j47AiHiOkJN69hJmcbGTHI0ImLmbYLHykhgeN0jVGola9yVjFgzCUklsZQMW55o+dW7IXv3RCXDzA==
+
 tslib@^2.4.0, tslib@^2.8.1:
   version "2.8.1"
   resolved "https://registry.yarnpkg.com/tslib/-/tslib-2.8.1.tgz#612efe4ed235d567e8aba5f2a5fab70280ade83f"
@@ -2558,6 +2617,11 @@ type-fest@^0.21.3:
   resolved "https://registry.yarnpkg.com/type-fest/-/type-fest-0.21.3.tgz#d260a24b0198436e133fa26a524a6d65fa3b2e37"
   integrity sha512-t0rzBq87m3fVcduHDUFhKmyyX+9eo6WQjZvf51Ea/M0Q7+T374Jp1aUiyUl0GKxp8M/OETVHSDvmkyPgvX+X2w==
 
+undici-types@~6.19.2:
+  version "6.19.8"
+  resolved "https://registry.yarnpkg.com/undici-types/-/undici-types-6.19.8.tgz#35111c9d1437ab83a7cdc0abae2f26d88eda0a02"
+  integrity sha512-ve2KP6f/JnbPBFyobGHuerC9g1FYGn/F8n1LWTwNxCEzd6IfqTwUQcNXgEtmmQ6DlRrC1hrSrBnCZPokRrDHjw==
+
 undici-types@~7.18.0:
   version "7.18.2"
   resolved "https://registry.yarnpkg.com/undici-types/-/undici-types-7.18.2.tgz#29357a89e7b7ca4aef3bf0fd3fd0cd73884229e9"
@@ -2661,6 +2725,11 @@ write-file-atomic@^5.0.1:
     imurmurhash "^0.1.4"
     signal-exit "^4.0.1"
 
+ws@8.17.1:
+  version "8.17.1"
+  resolved "https://registry.yarnpkg.com/ws/-/ws-8.17.1.tgz#9293da530bb548febc95371d90f9c878727d919b"
+  integrity sha512-6XQFvXTkbfUOZOKKILFG1PDK2NDQs4azKQl26T0YS5CxqWLgXajbPZ+h4gZekJyRqFU8pvnbAbbs/3TgRPy+GQ==
+
 y18n@^5.0.5:
   version "5.0.8"
   resolved "https://registry.yarnpkg.com/y18n/-/y18n-5.0.8.tgz#7f4934d0f7ca8c56f95314939ddcd2dd91ce1d55"