diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 73431fbfe..24defbf53 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -32,6 +32,11 @@ jobs:
         run: |
           deno fmt --check
           deno task test
+      - name: Run deno test for /x/dhkem-x25519
+        working-directory: ./x/dhkem-x25519
+        run: |
+          deno fmt --check
+          deno task test
       - name: Run deno test for /x/dhkem-secp256k1
         working-directory: ./x/dhkem-secp256k1
         run: |
diff --git a/.github/workflows/ci_browser.yml b/.github/workflows/ci_browser.yml
index 2fc14c7ee..a31eaa6e8 100644
--- a/.github/workflows/ci_browser.yml
+++ b/.github/workflows/ci_browser.yml
@@ -26,6 +26,8 @@ jobs:
           deno task minify > test/runtimes/browsers/pages/src/hpke.js
           mkdir test/runtimes/browsers/pages/core
           cp -rf core/test/runtimes/browsers/pages/* test/runtimes/browsers/pages/core
+          mkdir test/runtimes/browsers/pages/dhkem-x25519
+          cp -rf x/dhkem-x25519/test/runtimes/browsers/pages/* test/runtimes/browsers/pages/dhkem-x25519
           mkdir test/runtimes/browsers/pages/dhkem-secp256k1
           cp -rf x/dhkem-secp256k1/test/runtimes/browsers/pages/* test/runtimes/browsers/pages/dhkem-secp256k1
           deno task minify > test/runtimes/browsers/pages/dhkem-secp256k1/src/hpke.js
@@ -33,6 +35,11 @@ jobs:
         run: |
           deno task dnt
           deno task minify > ../test/runtimes/browsers/pages/core/src/hpke-core.js
+          deno task minify > ../test/runtimes/browsers/pages/dhkem-x25519/src/hpke-core.js
+      - working-directory: ./x/dhkem-x25519
+        run: |
+          deno task dnt
+          deno task minify > ../../test/runtimes/browsers/pages/dhkem-x25519/src/hpke-dhkem-x25519.js
       - working-directory: ./x/dhkem-secp256k1
         run: |
           deno task dnt
@@ -56,5 +63,7 @@ jobs:
           npx playwright test
       - working-directory: ./core/test/runtimes/browsers
         run: npm install && npx playwright install && npx playwright test
+      - working-directory: ./x/dhkem-x25519/test/runtimes/browsers
+        run: npm install && npx playwright install && npx playwright test
       - working-directory: ./x/dhkem-secp256k1/test/runtimes/browsers
         run: npm install && npx playwright install && npx playwright test
diff --git a/.github/workflows/ci_bun.yml b/.github/workflows/ci_bun.yml
index 1d74150df..48e46550f 100644
--- a/.github/workflows/ci_bun.yml
+++ b/.github/workflows/ci_bun.yml
@@ -39,16 +39,27 @@ jobs:
           nohup bun src/index.js &
           sleep 3
           deno test hpke.spec.ts --allow-net
-      - working-directory: ./core/
+      - working-directory: ./core
         run: |
           deno task dnt
           deno task minify > test/runtimes/hpke-core.js
+          deno task minify > ../x/dhkem-x25519/test/runtimes/hpke-core.js
       - name: Run test for core
         working-directory: ./core/test/runtimes/bun
         run: |
           nohup bun src/index.js &
           sleep 3
           deno test core.spec.ts --allow-net
+      - working-directory: ./x/dhkem-x25519
+        run: |
+          deno task dnt
+          deno task minify > test/runtimes/hpke-dhkem-x25519.js
+      - name: Run test for dhkem-x25519
+        working-directory: ./x/dhkem-x25519/test/runtimes/bun
+        run: |
+          nohup bun src/index.js &
+          sleep 3
+          deno test dhkem-x25519.spec.ts --allow-net
       - working-directory: ./x/dhkem-secp256k1/
         run: |
           deno task dnt
diff --git a/.github/workflows/ci_cloudflare.yml b/.github/workflows/ci_cloudflare.yml
index bf8dc00d7..f4cb77683 100644
--- a/.github/workflows/ci_cloudflare.yml
+++ b/.github/workflows/ci_cloudflare.yml
@@ -24,7 +24,6 @@ jobs:
           npm install -g esbuild
           deno task dnt
           deno task minify > test/runtimes/hpke.js
-          deno task minify > core/test/runtimes/hpke.js
           deno task minify > x/dhkem-secp256k1/test/runtimes/hpke.js
       - name: Run test
         working-directory: ./test/runtimes/cloudflare
@@ -33,10 +32,11 @@ jobs:
           nohup npm start &
           sleep 3
           deno test hpke.spec.ts --allow-net
-      - working-directory: ./core/
+      - working-directory: ./core
         run: |
           deno task dnt
           deno task minify > test/runtimes/hpke-core.js
+          deno task minify > ../x/dhkem-x25519/test/runtimes/hpke-core.js
       - name: Run test for core
         working-directory: ./core/test/runtimes/cloudflare
         run: |
@@ -44,7 +44,18 @@ jobs:
           nohup npm start &
           sleep 3
           deno test core.spec.ts --allow-net
-      - working-directory: ./x/dhkem-secp256k1/
+      - working-directory: ./x/dhkem-x25519
+        run: |
+          deno task dnt
+          deno task minify > test/runtimes/hpke-dhkem-x25519.js
+      - name: Run test for dhkem-x25519
+        working-directory: ./x/dhkem-x25519/test/runtimes/cloudflare
+        run: |
+          npm install
+          nohup npm start &
+          sleep 3
+          deno test dhkem-x25519.spec.ts --allow-net
+      - working-directory: ./x/dhkem-secp256k1
         run: |
           deno task dnt
           deno task minify > test/runtimes/hpke-dhkem-secp256k1.js
diff --git a/.github/workflows/ci_node.yml b/.github/workflows/ci_node.yml
index 22ebe5258..7979e8d4e 100644
--- a/.github/workflows/ci_node.yml
+++ b/.github/workflows/ci_node.yml
@@ -32,6 +32,11 @@ jobs:
         run: |
           deno task dnt
           deno task minify > ./npm/hpke-core.min.js
+      - name: Run dnt & minify for /x/dhkem-x25519
+        working-directory: ./x/dhkem-x25519
+        run: |
+          deno task dnt
+          deno task minify > ./npm/hpke-dhkem-x25519.min.js
       - name: Run dnt & minify for /x/dhkem-secp256k1
         working-directory: ./x/dhkem-secp256k1
         run: |
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index f0716fcb8..35051eccc 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -48,6 +48,28 @@ jobs:
         env:
           NODE_AUTH_TOKEN: ${{secrets.NPM_TOKEN}}
 
+  publish-dhkem-x25519:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 18
+          registry-url: https://registry.npmjs.org/
+      - uses: denoland/setup-deno@v1
+        with:
+          deno-version: v1.x
+      - name: Run dnt & minify
+        working-directory: ./x/dhkem-x25519
+        run: |
+          npm install -g esbuild
+          deno task dnt
+          deno task minify > ./npm/hpke-dhkem-x25519.min.js
+      - working-directory: ./x/dhkem-x25519/npm
+        run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{secrets.NPM_TOKEN}}
+
   publish-dhkem-secp256k1:
     runs-on: ubuntu-latest
     steps:
diff --git a/dnt.ts b/dnt.ts
index 9ced28770..4ed19b773 100644
--- a/dnt.ts
+++ b/dnt.ts
@@ -3,6 +3,7 @@ import { build, emptyDir } from "dnt";
 await emptyDir("./npm");
 await emptyDir("./core/npm");
 await emptyDir("./x/dhkem-secp256k1/npm");
+await emptyDir("./x/dhkem-x25519/npm");
 
 await build({
   entryPoints: ["./mod.ts"],
diff --git a/x/dhkem-x25519/README.md b/x/dhkem-x25519/README.md
new file mode 100644
index 000000000..c33884fc4
--- /dev/null
+++ b/x/dhkem-x25519/README.md
@@ -0,0 +1,247 @@
+<h1 align="center">@hpke/dhkem-x25519</h1>
+
+<div align="center">
+A TypeScript <a href="https://datatracker.ietf.org/doc/html/rfc9180">Hybrid Public Key Encryption (HPKE)</a> module extension for DH-KEM with X25519, which is implemented by using <a href="https://github.com/paulmillr/noble-curves">@noble/curves</a></div>
+<p></p>
+
+<div align="center">
+
+[Documentation](https://doc.deno.land/https://deno.land/x/hpke/x/dhkem-x25519/mod.ts)
+
+</div>
+
+## Index
+
+- [Supported Environments](#supported-environments)
+- [Installation](#installation)
+  - [Web Browser](#web-browser)
+  - [Node.js](#nodejs)
+  - [Deno](#deno)
+  - [Cloudflare Workers](#cloudflare-workers)
+- [Usage](#usage)
+- [Contributing](#contributing)
+
+## Supported Environments
+
+- **Web Browser**: [Web Cryptography API](https://www.w3.org/TR/WebCryptoAPI/)
+  supported browsers
+  - Confirmed: Chrome, Firefox, Edge, Safari, Opera, Vivaldi, Brave
+- **Node.js**: 16.x, 17.x, 18.x, 19.x, 20.x
+- **Deno**: 1.x (1.15-)
+- **Cloudflare Workers**
+- **bun**: 0.x (0.3.0-)
+
+## Installation
+
+### Web Browser
+
+Followings are how to use with typical CDNs. Other CDNs can be used as well.
+
+Using esm.sh:
+
+```html
+<!-- use a specific version -->
+<script type="module">
+  import * as hpke from "https://esm.sh/hpke-js@0.22.2";
+  import * as x25519 from "https://esm.sh/@hpke/dhkem-x25519@0.22.2";
+  // ...
+</script>
+
+<!-- use the latest stable version -->
+<script type="module">
+  import * as hpke from "https://esm.sh/hpke-js";
+  import * as x25519 from "https://esm.sh/@hpke/dhkem-x25519";
+  // ...
+</script>
+```
+
+Using unpkg:
+
+```html
+<!-- use a specific version -->
+<script type="module">
+  import * as hpke from "https://unpkg.com/hpke-js@0.22.2/esm/mod.js";
+  import * as x25519 from "https://unpkg.com/@hpke/dhkem-x25519@0.22.2/esm/mod.js";
+  // ...
+</script>
+```
+
+### Node.js
+
+Using npm:
+
+```sh
+npm install @hpke/dhkem-x25519
+```
+
+Using yarn:
+
+```sh
+yarn add @hpke/dhkem-x25519
+```
+
+### Deno
+
+Using deno.land:
+
+```js
+// use a specific version
+import * as hpke from "https://deno.land/x/hpke@0.22.2/mod.ts";
+import * as x25519 from "https://deno.land/x/hpke@0.22.2/x/dhkem-x25519/mod.ts";
+
+// use the latest stable version
+import * as hpke from "https://deno.land/x/hpke/mod.ts";
+import * as x25519 from "https://deno.land/x/hpke/x/dhkem-x25519/mod.ts";
+```
+
+### Cloudflare Workers
+
+Downloads a single js file from esm.sh:
+
+```sh
+curl -sS -o $YOUR_SRC_PATH/hpke.min.js https://esm.sh/v86/hpke-js@0.22.2/es2022/hpke.min.js
+curl -sS -o $YOUR_SRC_PATH/hpke-dhkem-x25519.min.js https://esm.sh/v86/@hpke/dhkem-x25519@0.22.2/es2022/hpke-dhkem-x25519.min.js
+```
+
+## Usage
+
+This section shows some typical usage examples.
+
+### Browsers
+
+```html
+<html>
+  <head></head>
+  <body>
+    <script type="module">
+      // import * as hpke from "https://esm.sh/hpke-js@0.22.2";
+      import { KdfId, AeadId, CipherSuite } from "https://esm.sh/hpke-js@0.22.2";
+      import { DhkemX25519HkdfSha256 } from "https://esm.sh/@hpke/dhkem-x25519@0.22.2";
+
+      globalThis.doHpke = async () => {
+
+        const suite = new CipherSuite({
+          kem: new DhkemX25519HkdfSha256(),
+          kdf: KdfId.HkdfSha256,
+          aead: AeadId.Aes128Gcm
+        });
+ 
+        const rkp = await suite.generateKeyPair();
+      
+        const sender = await suite.createSenderContext({
+          recipientPublicKey: rkp.publicKey
+        });
+
+        const recipient = await suite.createRecipientContext({
+          recipientKey: rkp.privateKey, // rkp (CryptoKeyPair) is also acceptable.
+          enc: sender.enc,
+        });
+
+        // encrypt
+        const ct = await sender.seal(new TextEncoder().encode("hello world!"));
+      
+        // decrypt
+        try {
+          const pt = await recipient.open(ct);
+
+          // hello world!
+          alert(new TextDecoder().decode(pt));
+        } catch (err) {
+          alert("failed to decrypt.");
+        }
+      }
+      
+    </script>
+    <button type="button" onclick="doHpke()">do HPKE</button>
+  </body>
+</html>
+```
+
+### Node.js
+
+```js
+const { KdfId, AeadId, CipherSuite } = require("hpke-js");
+const { DhkemX25519HkdfSha256 } = require("@hpke/dhkem-x25519");
+
+async function doHpke() {
+  // setup
+  const suite = new CipherSuite({
+    kem: new DhkemX25519HkdfSha256(),
+    kdf: KdfId.HkdfSha256,
+    aead: AeadId.Aes128Gcm,
+  });
+
+  const rkp = await suite.generateKeyPair();
+
+  const sender = await suite.createSenderContext({
+    recipientPublicKey: rkp.publicKey,
+  });
+
+  const recipient = await suite.createRecipientContext({
+    recipientKey: rkp.privateKey,
+    enc: sender.enc,
+  });
+
+  // encrypt
+  const ct = await sender.seal(new TextEncoder().encode("my-secret-message"));
+
+  // decrypt
+  try {
+    const pt = await recipient.open(ct);
+
+    console.log("decrypted: ", new TextDecoder().decode(pt));
+    // decrypted: my-secret-message
+  } catch (err) {
+    console.log("failed to decrypt.");
+  }
+}
+
+doHpke();
+```
+
+### Deno
+
+```js
+import { KdfId, AeadId, CipherSuite } from "https://deno.land/x/hpke@0.22.2/mod.ts";
+import { DhkemX25519HkdfSha256 } from "https://deno.land/x/hpke@0.22.2/x/dhkem-x25519/mod.ts";
+
+async function doHpke() {
+  // setup
+  const suite = new CipherSuite({
+    kem: new DhkemX25519HkdfSha256(),
+    kdf: KdfId.HkdfSha256,
+    aead: AeadId.Aes128Gcm,
+  });
+
+  const rkp = await suite.generateKeyPair();
+
+  const sender = await suite.createSenderContext({
+    recipientPublicKey: rkp.publicKey,
+  });
+
+  const recipient = await suite.createRecipientContext({
+    recipientKey: rkp.privateKey,
+    enc: sender.enc,
+  });
+
+  // encrypt
+  const ct = await sender.seal(new TextEncoder().encode("my-secret-message"));
+
+  try {
+    // decrypt
+    const pt = await recipient.open(ct);
+
+    console.log("decrypted: ", new TextDecoder().decode(pt));
+    // decrypted: my-secret-message
+  } catch (_err: unknown) {
+    console.log("failed to decrypt.");
+  }
+}
+
+doHpke();
+```
+
+## Contributing
+
+We welcome all kind of contributions, filing issues, suggesting new features or
+sending PRs.
diff --git a/x/dhkem-x25519/deno.json b/x/dhkem-x25519/deno.json
new file mode 100644
index 000000000..b795a6814
--- /dev/null
+++ b/x/dhkem-x25519/deno.json
@@ -0,0 +1,33 @@
+{
+  "imports": {
+    "testing/": "https://deno.land/std@0.195.0/testing/",
+    "dnt": "https://deno.land/x/dnt@0.38.0/mod.ts"
+  },
+  "fmt": {
+    "include": [
+      "deno.json",
+      "dnt.ts",
+      "mod.ts",
+      "test/"
+    ],
+    "exclude": [
+      "test/runtimes/bun",
+      "test/runtimes/browsers/node_modules",
+      "test/runtimes/cloudflare"
+    ]
+  },
+  "lint": {
+    "include": ["mod.ts", "test/"],
+    "exclude": [
+      "test/runtimes/bun",
+      "test/runtimes/browsers/node_modules",
+      "test/runtimes/cloudflare"
+    ]
+  },
+  "tasks": {
+    "test": "deno fmt && deno lint && deno test test -A --fail-fast --doc --coverage=coverage --parallel --allow-read",
+    "cov": "deno coverage ./coverage --lcov --exclude='test'",
+    "dnt": "deno run -A dnt.ts $(git describe --tags $(git rev-list --tags --max-count=1))",
+    "minify": "esbuild npm/esm/x/dhkem-x25519/mod.js --bundle --format=esm --minify"
+  }
+}
diff --git a/x/dhkem-x25519/deno.lock b/x/dhkem-x25519/deno.lock
new file mode 100644
index 000000000..ceeaa3fdc
--- /dev/null
+++ b/x/dhkem-x25519/deno.lock
@@ -0,0 +1,185 @@
+{
+  "version": "2",
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+    "https://deno.land/x/hpke@0.21.0/src/kems/dhkemPrimitives/ec.ts": "57eee1dd96ad7a48de8cc69d20918c956a397a8d597c0b6ee0e68b85970f473e",
+    "https://deno.land/x/hpke@0.21.0/src/kems/dhkemPrimitives/secp256k1.ts": "74be448865e2800a18ba70419758713c417bf74de66f3d344387317f4cb39072",
+    "https://deno.land/x/hpke@0.21.0/src/kems/dhkemPrimitives/x25519.ts": "1b211e210df98252cb45c45028f77772a0962d3ae403ee48e1160b8620e92438",
+    "https://deno.land/x/hpke@0.21.0/src/kems/dhkemPrimitives/x448.ts": "bf17c0ccb58abe9efa12d38ed7ad494eea89d1cd55739a3648ed055f45d1f59a",
+    "https://deno.land/x/hpke@0.21.0/src/recipientContext.ts": "228ba51bc52df0387617a3f471d43b3ec4f7b6d142c0f7f395d282a09f6ceae9",
+    "https://deno.land/x/hpke@0.21.0/src/senderContext.ts": "e4a4381b9dfbae61309c5ed4fe92db973df57b704c6d200afe8bfc4a3e845e47",
+    "https://deno.land/x/hpke@0.21.0/src/utils/bignum.ts": "2e8749a21cde3ec81e4d353ec001732d60c22d56a717f83bec4c9ddf8227f75c",
+    "https://deno.land/x/hpke@0.21.0/src/utils/misc.ts": "9ec825918998d8df2593571b722d9e4344081152ef9f68012431226960bb2dfd",
+    "https://deno.land/x/hpke@0.21.0/src/webCrypto.ts": "60296a8b402f93a6622b57d140299fe524c3bce334dbf46a23a37b2c520f6f89",
+    "https://deno.land/x/hpke@0.21.0/src/xCryptoKey.ts": "93355b8422f3477b62e2d048ec0c766ccd6c36bfe0649345f092239a984edc2d",
+    "https://deno.land/x/ts_morph@18.0.0/bootstrap/mod.ts": "b53aad517f106c4079971fcd4a81ab79fadc40b50061a3ab2b741a09119d51e9",
+    "https://deno.land/x/ts_morph@18.0.0/bootstrap/ts_morph_bootstrap.js": "6645ac03c5e6687dfa8c78109dc5df0250b811ecb3aea2d97c504c35e8401c06",
+    "https://deno.land/x/ts_morph@18.0.0/common/DenoRuntime.ts": "6a7180f0c6e90dcf23ccffc86aa8271c20b1c4f34c570588d08a45880b7e172d",
+    "https://deno.land/x/ts_morph@18.0.0/common/mod.ts": "01985d2ee7da8d1caee318a9d07664774fbee4e31602bc2bb6bb62c3489555ed",
+    "https://deno.land/x/ts_morph@18.0.0/common/ts_morph_common.js": "845671ca951073400ce142f8acefa2d39ea9a51e29ca80928642f3f8cf2b7700",
+    "https://deno.land/x/ts_morph@18.0.0/common/typescript.js": "d5c598b6a2db2202d0428fca5fd79fc9a301a71880831a805d778797d2413c59",
+    "https://deno.land/x/wasmbuild@0.14.1/cache.ts": "89eea5f3ce6035a1164b3e655c95f21300498920575ade23161421f5b01967f4",
+    "https://deno.land/x/wasmbuild@0.14.1/loader.ts": "d98d195a715f823151cbc8baa3f32127337628379a02d9eb2a3c5902dbccfc02"
+  },
+  "npm": {
+    "specifiers": {
+      "@noble/ciphers@0.1.4": "@noble/ciphers@0.1.4",
+      "@noble/curves@1.1.0": "@noble/curves@1.1.0",
+      "@noble/hashes@1.3.1": "@noble/hashes@1.3.1"
+    },
+    "packages": {
+      "@noble/ciphers@0.1.4": {
+        "integrity": "sha512-d3ZR8vGSpy3v/nllS+bD/OMN5UZqusWiQqkyj7AwzTnhXFH72pF5oB4Ach6DQ50g5kXxC28LdaYBEpsyv9KOUQ==",
+        "dependencies": {}
+      },
+      "@noble/curves@1.1.0": {
+        "integrity": "sha512-091oBExgENk/kGj3AZmtBDMpxQPDtxQABR2B9lb1JbVTs6ytdzZNwvhxQ4MWasRNEzlbEH8jCWFCwhF/Obj5AA==",
+        "dependencies": {
+          "@noble/hashes": "@noble/hashes@1.3.1"
+        }
+      },
+      "@noble/hashes@1.3.1": {
+        "integrity": "sha512-EbqwksQwz9xDRGfDST86whPBgM65E0OH/pCgqW0GBVzO22bNE+NuIbeTb714+IfSjU3aRk47EUvXIb5bTsenKA==",
+        "dependencies": {}
+      }
+    }
+  }
+}
diff --git a/x/dhkem-x25519/dnt.ts b/x/dhkem-x25519/dnt.ts
new file mode 100644
index 000000000..78fa9b42d
--- /dev/null
+++ b/x/dhkem-x25519/dnt.ts
@@ -0,0 +1,61 @@
+import { build, emptyDir } from "dnt";
+
+await emptyDir("./npm");
+
+await build({
+  entryPoints: ["./mod.ts"],
+  outDir: "./npm",
+  typeCheck: false,
+  test: true,
+  declaration: true,
+  scriptModule: "umd",
+  importMap: "./deno.json",
+  compilerOptions: {
+    lib: ["es2021", "dom"],
+  },
+  shims: {
+    deno: "dev",
+  },
+  package: {
+    name: "@hpke/dhkem-x25519",
+    version: Deno.args[0],
+    description:
+      "A Hybrid Public Key Encryption (HPKE) module extension for X25519",
+    repository: {
+      type: "git",
+      url: "git+https://github.com/dajiaji/hpke-js.git",
+    },
+    homepage: "https://github.com/dajiaji/hpke-js#readme",
+    license: "MIT",
+    main: "./script/x/dhkem-x25519/mod.js",
+    types: "./script/x/dhkem-x25519/mod.d.ts",
+    exports: {
+      ".": {
+        "import": "./esm/x/dhkem-x25519/mod.js",
+        "require": "./script/x/dhkem-x25519/mod.js",
+      },
+      "./package.json": "./package.json",
+    },
+    keywords: [
+      "hpke",
+      "rfc9180",
+      "kem",
+      "hkdf",
+      "dh",
+      "x25519",
+      "security",
+      "encryption",
+    ],
+    engines: {
+      "node": ">=16.0.0",
+    },
+    author: "Ajitomi Daisuke",
+    bugs: {
+      url: "https://github.com/dajiaji/hpke-js/issues",
+    },
+  },
+});
+
+// post build steps
+Deno.copyFileSync("../../LICENSE", "npm/LICENSE");
+Deno.copyFileSync("README.md", "npm/README.md");
diff --git a/x/dhkem-x25519/mod.ts b/x/dhkem-x25519/mod.ts
new file mode 100644
index 000000000..c91129eaf
--- /dev/null
+++ b/x/dhkem-x25519/mod.ts
@@ -0,0 +1 @@
+export { DhkemX25519HkdfSha256 } from "../../src/kems/dhkemX25519.ts";
diff --git a/x/dhkem-x25519/test/dhkem-x25519.test.ts b/x/dhkem-x25519/test/dhkem-x25519.test.ts
new file mode 100644
index 000000000..c970236cd
--- /dev/null
+++ b/x/dhkem-x25519/test/dhkem-x25519.test.ts
@@ -0,0 +1,228 @@
+import { assertEquals, assertRejects } from "testing/asserts.ts";
+import { describe, it } from "testing/bdd.ts";
+
+import { AeadId, CipherSuite, KdfId, KemId } from "../../../mod.ts";
+// } from "https://deno.land/x/hpke/mod.ts";
+
+import { DhkemX25519HkdfSha256 } from "../mod.ts";
+import { loadCrypto, loadSubtleCrypto } from "./utils.ts";
+
+describe("DhkemX25519HkdfSha256", () => {
+  describe("with valid parameters", () => {
+    it("should have a correct KEM object", async () => {
+      const api = await loadSubtleCrypto();
+
+      // assert
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+      assertEquals(typeof kem, "object");
+      assertEquals(kem.id, KemId.DhkemX25519HkdfSha256);
+      assertEquals(kem.secretSize, 32);
+      assertEquals(kem.encSize, 32);
+      assertEquals(kem.publicKeySize, 32);
+      assertEquals(kem.privateKeySize, 32);
+    });
+  });
+});
+
+describe("generateKeyPair", () => {
+  describe("with valid parameters", () => {
+    it("should return a proper instance", async () => {
+      const api = await loadSubtleCrypto();
+
+      // assert
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+      const kp = await kem.generateKeyPair();
+      assertEquals(kp.publicKey.type, "public");
+      assertEquals(kp.publicKey.extractable, true);
+      assertEquals(kp.publicKey.algorithm.name, "X25519");
+      // assertEquals(kp.publicKey.algorithm.namedCurve, "X25519");
+      assertEquals(kp.publicKey.usages.length, 0);
+      // assertEquals(kp.publicKey.usages[0], "deriveBits");
+      assertEquals(kp.privateKey.type, "private");
+      assertEquals(kp.privateKey.extractable, true);
+      assertEquals(kp.privateKey.algorithm.name, "X25519");
+      // assertEquals(kp.privateKey.algorithm.namedCurve, "X25519");
+      assertEquals(kp.privateKey.usages.length, 1);
+      assertEquals(kp.privateKey.usages[0], "deriveBits");
+    });
+  });
+});
+
+describe("deriveKeyPair", () => {
+  describe("with valid parameters", () => {
+    it("should return a proper instance", async () => {
+      const api = await loadSubtleCrypto();
+      const cryptoApi = await loadCrypto();
+
+      // assert
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+      const ikm = new Uint8Array(32);
+      cryptoApi.getRandomValues(ikm);
+      const kp = await kem.deriveKeyPair(ikm.buffer);
+      assertEquals(kp.publicKey.type, "public");
+      assertEquals(kp.publicKey.extractable, true);
+      assertEquals(kp.publicKey.algorithm.name, "X25519");
+      // assertEquals(kp.publicKey.algorithm.namedCurve, "X25519");
+      assertEquals(kp.publicKey.usages.length, 0);
+      // assertEquals(kp.publicKey.usages[0], "deriveBits");
+      assertEquals(kp.privateKey.type, "private");
+      assertEquals(kp.privateKey.extractable, true);
+      assertEquals(kp.privateKey.algorithm.name, "X25519");
+      // assertEquals(kp.privateKey.algorithm.namedCurve, "X25519");
+      assertEquals(kp.privateKey.usages.length, 1);
+      assertEquals(kp.privateKey.usages[0], "deriveBits");
+    });
+  });
+});
+
+describe("serialize/deserializePublicKey", () => {
+  describe("with valid parameters", () => {
+    it("should return a proper instance with DhkemX25519HkdfSha256", async () => {
+      const api = await loadSubtleCrypto();
+
+      // assert
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+      const kp = await kem.generateKeyPair();
+      const bPubKey = await kem.serializePublicKey(kp.publicKey);
+      const pubKey = await kem.deserializePublicKey(bPubKey);
+      assertEquals(pubKey.type, "public");
+      assertEquals(pubKey.extractable, true);
+      assertEquals(pubKey.algorithm.name, "X25519");
+      // assertEquals(pubKey.algorithm.namedCurve, "X25519");
+      assertEquals(pubKey.usages.length, 0);
+      // assertEquals(pubKey.usages[0], "deriveBits");
+    });
+  });
+});
+
+describe("importKey", () => {
+  describe("with valid parameters", () => {
+    it("should return a valid private key for DhkemX25519HkdfSha256 from raw key", async () => {
+      const api = await loadSubtleCrypto();
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+
+      const cryptoApi = await loadCrypto();
+      const rawKey = new Uint8Array(32);
+      cryptoApi.getRandomValues(rawKey);
+      const privKey = await kem.importKey("raw", rawKey, false);
+
+      // assert
+      assertEquals(privKey.usages.length, 1);
+      assertEquals(privKey.usages[0], "deriveBits");
+    });
+
+    it("should return a valid public key for DhkemX25519HkdfSha256 from raw key", async () => {
+      const api = await loadSubtleCrypto();
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+
+      const cryptoApi = await loadCrypto();
+      const rawKey = new Uint8Array(32);
+      cryptoApi.getRandomValues(rawKey);
+      const privKey = await kem.importKey("raw", rawKey, true);
+
+      // assert
+      assertEquals(privKey.usages.length, 0);
+      // assertEquals(privKey.usages[0], "deriveBits");
+    });
+  });
+
+  describe("with invalid parameters", () => {
+    it("should throw DeserializeError with invalid DhkemX25519HkdfSha256 private key", async () => {
+      const api = await loadSubtleCrypto();
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+
+      const cryptoApi = await loadCrypto();
+      const rawKey = new Uint8Array(33);
+      cryptoApi.getRandomValues(rawKey);
+
+      // assert
+      await assertRejects(
+        () => kem.importKey("raw", rawKey, false),
+        Error,
+      );
+    });
+
+    it("should throw DeserializeError with invalid DhkemX25519HkdfSha256 public key", async () => {
+      const api = await loadSubtleCrypto();
+      const kem = new DhkemX25519HkdfSha256();
+      kem.init(api);
+
+      const cryptoApi = await loadCrypto();
+      const rawKey = new Uint8Array(33);
+      cryptoApi.getRandomValues(rawKey);
+
+      // assert
+      await assertRejects(
+        () => kem.importKey("raw", rawKey, true),
+        Error,
+      );
+    });
+  });
+});
+
+describe("CipherSuite", () => {
+  describe("constructor with DhkemX25519HkdfSha256", () => {
+    it("should have a correct ciphersuite", () => {
+      const suite: CipherSuite = new CipherSuite({
+        kem: new DhkemX25519HkdfSha256(),
+        kdf: KdfId.HkdfSha256,
+        aead: AeadId.ExportOnly,
+      });
+      assertEquals(suite.kem.secretSize, 32);
+      assertEquals(suite.kem.encSize, 32);
+      assertEquals(suite.kem.publicKeySize, 32);
+      assertEquals(suite.kem.privateKeySize, 32);
+
+      // assert
+      assertEquals(suite.kem.id, KemId.DhkemX25519HkdfSha256);
+      assertEquals(suite.kem.id, 0x0020);
+      assertEquals(suite.kdf.id, KdfId.HkdfSha256);
+      assertEquals(suite.kdf.id, 0x0001);
+      assertEquals(suite.aead.id, AeadId.ExportOnly);
+      assertEquals(suite.aead.id, 0xFFFF);
+    });
+  });
+
+  describe("A README example of DhkemX25519HkdfSha256", () => {
+    it("should work normally", async () => {
+      // setup
+      const kem = new DhkemX25519HkdfSha256();
+      const suite = new CipherSuite({
+        kem: kem,
+        kdf: KdfId.HkdfSha256,
+        aead: AeadId.Aes128Gcm,
+      });
+
+      const rkp = await suite.generateKeyPair();
+
+      const sender = await suite.createSenderContext({
+        recipientPublicKey: rkp.publicKey,
+      });
+
+      const recipient = await suite.createRecipientContext({
+        recipientKey: rkp,
+        enc: sender.enc,
+      });
+      assertEquals(sender.enc.byteLength, kem.encSize);
+      assertEquals(sender.enc.byteLength, kem.publicKeySize);
+
+      // encrypt
+      const ct = await sender.seal(
+        new TextEncoder().encode("my-secret-message"),
+      );
+
+      // decrypt
+      const pt = await recipient.open(ct);
+
+      // assert
+      assertEquals(new TextDecoder().decode(pt), "my-secret-message");
+    });
+  });
+});
diff --git a/x/dhkem-x25519/test/runtimes/browsers/dhkem-x25519.spec.ts b/x/dhkem-x25519/test/runtimes/browsers/dhkem-x25519.spec.ts
new file mode 100644
index 000000000..599412640
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/browsers/dhkem-x25519.spec.ts
@@ -0,0 +1,9 @@
+import { expect, test } from "@playwright/test";
+
+test("basic test", async ({ page }) => {
+  await page.goto("https://dajiaji.github.io/hpke-js/dhkem-x25519");
+  await page.click("text=run");
+  await page.waitForTimeout(5000);
+  await expect(page.locator("id=pass")).toHaveText("6");
+  await expect(page.locator("id=fail")).toHaveText("0");
+});
diff --git a/x/dhkem-x25519/test/runtimes/browsers/package.json b/x/dhkem-x25519/test/runtimes/browsers/package.json
new file mode 100644
index 000000000..22ec1425b
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/browsers/package.json
@@ -0,0 +1,5 @@
+{
+  "devDependencies": {
+    "@playwright/test": "^1.36.1"
+  }
+}
diff --git a/x/dhkem-x25519/test/runtimes/browsers/pages/index.html b/x/dhkem-x25519/test/runtimes/browsers/pages/index.html
new file mode 100644
index 000000000..8f0788ff2
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/browsers/pages/index.html
@@ -0,0 +1,86 @@
+<html>
+  <head><title>@hpke/dhkem-x25519 test</title></head>
+  <body>
+    <script type="module">
+      import { KdfId, AeadId, CipherSuite } from './src/hpke-core.js';
+      import { DhkemX25519HkdfSha256 } from './src/hpke-dhkem-x25519.js';
+
+      const kdfs = [
+        KdfId.HkdfSha256,
+        KdfId.HkdfSha384,
+        KdfId.HkdfSha512,
+      ];
+
+      const aeads = [
+        AeadId.Aes128Gcm,
+        AeadId.Aes256Gcm,
+      ];
+
+      globalThis.run = async () => {
+        let pass = 0;
+        let fail = 0;
+        const kem = new DhkemX25519HkdfSha256();
+        for (const kdf of kdfs) {
+          for (const aead of aeads) {
+            try {
+              const suite = new CipherSuite({ kem: kem, kdf: kdf, aead: aead });
+      
+              const rkp = await suite.generateKeyPair();
+      
+              const sender = await suite.createSenderContext({
+                recipientPublicKey: rkp.publicKey
+              });
+      
+              const recipient = await suite.createRecipientContext({
+                recipientKey: rkp,
+                enc: sender.enc,
+              });
+      
+              // encrypt
+              const ct = await sender.seal(new TextEncoder().encode('hello world!'));
+      
+              // decrypt
+              const pt = await recipient.open(ct);
+
+              // hello world!
+              'hello world!' === new TextDecoder().decode(pt) ? pass++ : fail++;
+
+            } catch (e) {
+              fail++;
+            }
+          }
+        }
+        document.getElementById("pass").innerHTML = pass;
+        document.getElementById("fail").innerHTML = fail;
+      }
+
+      globalThis.reset = () => {
+        document.getElementById("pass").innerHTML = "-";
+        document.getElementById("fail").innerHTML = "-";
+      }
+      
+    </script>
+
+    <h1><a href="https://github.com/dajiaji/hpke-js">@hpke/dhkem-x25519</a> test</h1>
+
+    <div id="operation">
+      <button type="button" onclick="run()">run</button>
+      <button type="button" onclick="reset()">reset</button>
+    </div>
+
+    <br>
+
+    <div id="test">  
+      <table>
+        <tr>
+          <th><font color="green">pass: </font></th>
+          <td id="pass">-</td>
+        </tr>
+        <tr>
+          <th><font color="red">fail: </font></th>
+          <td id="fail">-</td>
+        </tr>
+      </table>
+    </div>
+  </body>
+</html>
diff --git a/x/dhkem-x25519/test/runtimes/browsers/pages/src/.gitkeep b/x/dhkem-x25519/test/runtimes/browsers/pages/src/.gitkeep
new file mode 100644
index 000000000..e69de29bb
diff --git a/x/dhkem-x25519/test/runtimes/browsers/playwright.config.ts b/x/dhkem-x25519/test/runtimes/browsers/playwright.config.ts
new file mode 100644
index 000000000..ec692f847
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/browsers/playwright.config.ts
@@ -0,0 +1,20 @@
+// playwright.config.ts
+import { devices, PlaywrightTestConfig } from "@playwright/test";
+
+const config: PlaywrightTestConfig = {
+  projects: [
+    {
+      name: "chromium",
+      use: { ...devices["Desktop Chrome"] },
+    },
+    {
+      name: "firefox",
+      use: { ...devices["Desktop Firefox"] },
+    },
+    {
+      name: "webkit",
+      use: { ...devices["Desktop Safari"] },
+    },
+  ],
+};
+export default config;
diff --git a/x/dhkem-x25519/test/runtimes/bun/dhkem-x25519.spec.ts b/x/dhkem-x25519/test/runtimes/bun/dhkem-x25519.spec.ts
new file mode 100644
index 000000000..d5aa70dbc
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/bun/dhkem-x25519.spec.ts
@@ -0,0 +1,17 @@
+import { assertEquals } from "testing/asserts.ts";
+import { describe, it } from "testing/bdd.ts";
+
+describe("Bun", () => {
+  describe("GET /test", () => {
+    it("should return ok", async () => {
+      for (const kdf of ["0x0001", "0x0002", "0x0003"]) {
+        for (const aead of ["0x0001", "0x0002"]) {
+          const res = await fetch(
+            `http://localhost:3003/test?kdf=${kdf}&aead=${aead}`,
+          );
+          assertEquals("ok", await res.text());
+        }
+      }
+    });
+  });
+});
diff --git a/x/dhkem-x25519/test/runtimes/bun/src/index.js b/x/dhkem-x25519/test/runtimes/bun/src/index.js
new file mode 100644
index 000000000..41f93783c
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/bun/src/index.js
@@ -0,0 +1,8 @@
+import { testServer } from "../../server.js";
+
+export default {
+  port: 3003,
+  async fetch(request) {
+    return await testServer(request);
+  },
+};
diff --git a/x/dhkem-x25519/test/runtimes/cloudflare/dhkem-x25519.spec.ts b/x/dhkem-x25519/test/runtimes/cloudflare/dhkem-x25519.spec.ts
new file mode 100644
index 000000000..40ff9cb74
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/cloudflare/dhkem-x25519.spec.ts
@@ -0,0 +1,17 @@
+import { assertEquals } from "testing/asserts.ts";
+import { describe, it } from "testing/bdd.ts";
+
+describe("Cloudflare Workers", () => {
+  describe("GET /test", () => {
+    it("should return ok", async () => {
+      for (const kdf of ["0x0001", "0x0002", "0x0003"]) {
+        for (const aead of ["0x0001", "0x0002"]) {
+          const res = await fetch(
+            `http://localhost:8788/test?kdf=${kdf}&aead=${aead}`,
+          );
+          assertEquals("ok", await res.text());
+        }
+      }
+    });
+  });
+});
diff --git a/x/dhkem-x25519/test/runtimes/cloudflare/package.json b/x/dhkem-x25519/test/runtimes/cloudflare/package.json
new file mode 100644
index 000000000..0b9a27570
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/cloudflare/package.json
@@ -0,0 +1,12 @@
+{
+  "name": "wrangler",
+  "version": "0.1.0",
+  "devDependencies": {
+    "wrangler": "^3.3.0"
+  },
+  "private": true,
+  "scripts": {
+    "start": "wrangler dev --port 8790",
+    "deploy": "wrangler publish"
+  }
+}
diff --git a/x/dhkem-x25519/test/runtimes/cloudflare/src/index.js b/x/dhkem-x25519/test/runtimes/cloudflare/src/index.js
new file mode 100644
index 000000000..2b1b697ea
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/cloudflare/src/index.js
@@ -0,0 +1,7 @@
+import { testServer } from "../../server.js";
+
+export default {
+  async fetch(request) {
+    return await testServer(request);
+  },
+};
diff --git a/x/dhkem-x25519/test/runtimes/cloudflare/wrangler.toml b/x/dhkem-x25519/test/runtimes/cloudflare/wrangler.toml
new file mode 100644
index 000000000..ee79b9b87
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/cloudflare/wrangler.toml
@@ -0,0 +1,4 @@
+name = "wrangler"
+main = "src/index.js"
+compatibility_date = "2022-07-01"
+node_compat = true
diff --git a/x/dhkem-x25519/test/runtimes/server.js b/x/dhkem-x25519/test/runtimes/server.js
new file mode 100644
index 000000000..bf0f85cb6
--- /dev/null
+++ b/x/dhkem-x25519/test/runtimes/server.js
@@ -0,0 +1,41 @@
+import * as hpke from "./hpke-core.js";
+import { DhkemX25519HkdfSha256 } from "./hpke-dhkem-x25519.js";
+
+export async function testServer(request) {
+  const url = new URL(request.url);
+  if (url.pathname !== "/test") {
+    return new Response("ng: invalid path");
+  }
+  const params = url.searchParams;
+  const kdfStr = params.get("kdf");
+  const aeadStr = params.get("aead");
+  if (kdfStr === null || aeadStr === null) {
+    return new Response("ng: invalid params");
+  }
+  const kem = new DhkemX25519HkdfSha256();
+  const kdf = Number.parseInt(kdfStr);
+  const aead = Number.parseInt(aeadStr);
+  if (Number.isNaN(kdf) || Number.isNaN(aead)) {
+    return new Response("ng: invalid params");
+  }
+
+  try {
+    const suite = new hpke.CipherSuite({ kem: kem, kdf: kdf, aead: aead });
+    const rkp = await suite.generateKeyPair();
+    const sender = await suite.createSenderContext({
+      recipientPublicKey: rkp.publicKey,
+    });
+    const recipient = await suite.createRecipientContext({
+      recipientKey: rkp,
+      enc: sender.enc,
+    });
+    const ct = await sender.seal(new TextEncoder().encode("hello world!"));
+    const pt = await recipient.open(ct);
+    if ("hello world!" !== new TextDecoder().decode(pt)) {
+      return new Response("ng");
+    }
+  } catch (e) {
+    return new Response("ng: " + e.message);
+  }
+  return new Response("ok");
+}
diff --git a/x/dhkem-x25519/test/utils.ts b/x/dhkem-x25519/test/utils.ts
new file mode 100644
index 000000000..830172325
--- /dev/null
+++ b/x/dhkem-x25519/test/utils.ts
@@ -0,0 +1,48 @@
+export const isBrowser = () => typeof window !== "undefined";
+
+export const isCloudflareWorkers = () => typeof caches !== "undefined";
+
+export function hexStringToBytes(v: string): Uint8Array {
+  if (v.length === 0) {
+    return new Uint8Array([]);
+  }
+  const res = v.match(/[\da-f]{2}/gi);
+  if (res == null) {
+    throw new Error("hexStringToBytes: not hex string");
+  }
+  return new Uint8Array(res.map(function (h) {
+    return parseInt(h, 16);
+  }));
+}
+
+export async function loadCrypto(): Promise<Crypto> {
+  if (isBrowser() || isCloudflareWorkers()) {
+    if (globalThis.crypto !== undefined) {
+      return globalThis.crypto;
+    }
+    // jsdom
+  }
+
+  try {
+    const { webcrypto } = await import("crypto"); // node:crypto
+    return (webcrypto as unknown as Crypto);
+  } catch (_e: unknown) {
+    throw new Error("Web Cryptograph API not supported");
+  }
+}
+
+export async function loadSubtleCrypto(): Promise<SubtleCrypto> {
+  if (isBrowser() || isCloudflareWorkers()) {
+    if (globalThis.crypto !== undefined) {
+      return globalThis.crypto.subtle;
+    }
+    // jsdom
+  }
+
+  try {
+    const { webcrypto } = await import("crypto"); // node:crypto
+    return (webcrypto as unknown as Crypto).subtle;
+  } catch (_e: unknown) {
+    throw new Error("Web Cryptograph API not supported");
+  }
+}