From 6106c68a03919bc1db5f8c5b78a8b51d87f64661 Mon Sep 17 00:00:00 2001
From: Hatter Jiang <jht5945@gmail.com>
Date: Tue, 21 Jan 2025 01:19:46 +0800
Subject: [PATCH] feat: add deno-wrapkey-mod.ts

---
 libraries/deno-wrapkey-mod.ts | 139 ++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 libraries/deno-wrapkey-mod.ts

diff --git a/libraries/deno-wrapkey-mod.ts b/libraries/deno-wrapkey-mod.ts
new file mode 100644
index 0000000..2fbf13b
--- /dev/null
+++ b/libraries/deno-wrapkey-mod.ts
@@ -0,0 +1,139 @@
+import { crypto } from "jsr:@std/crypto";
+import { encodeBase64Url } from "jsr:@std/encoding/base64url";
+import { decodeHex } from "jsr:@std/encoding/hex";
+
+const {
+    createECDH,
+    getRandomValues,
+} = await import("node:crypto");
+
+// Reference:
+// - https://docs.deno.com/api/node/crypto/~/ECDH
+// - https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/encrypt
+
+class EcdhEphemeral {
+    ePublicKey: Uint8Array;
+    sharedSecret: ArrayBufferLike;
+
+    constructor(ePublicKey: Uint8Array, sharedSecret: ArrayBufferLike) {
+        this.ePublicKey = ePublicKey;
+        this.sharedSecret = sharedSecret;
+    }
+}
+
+class Ecdh {
+    publicKeyPoint: Uint8Array;
+
+    constructor(publicKeyPoint: Uint8Array) {
+        this.publicKeyPoint = publicKeyPoint;
+    }
+
+    static fromHex(publicKeyPointHex: string): Ecdh {
+        return new Ecdh(decodeHex(publicKeyPointHex));
+    }
+
+    ecdh(): EcdhEphemeral {
+        const bitLength = ((this.publicKeyPoint.length - 1) / 2) * 8;
+        if (bitLength !== 256) {
+            // NOTICE current only supports P256
+            throw `Invalid EC public key point, bit length: ${bitLength}`;
+        }
+        const temp = createECDH(`secp${bitLength}r1`);
+        const ePublicKey = temp.generateKeys();
+        const sharedSecret = temp.computeSecret(this.publicKeyPoint);
+        return new EcdhEphemeral(ePublicKey, sharedSecret);
+    }
+}
+
+async function simpleKdf256(
+    input: ArrayBufferLike,
+): Promise<ArrayBuffer> {
+    const SHA256 = "SHA-256";
+    for (let i = 0; i < 8; i++) {
+        input = await crypto.subtle.digest(SHA256, input);
+    }
+    return input;
+}
+
+function randomNonce(): ArrayBufferLike {
+    const buffer = new Uint8Array(12);
+    getRandomValues(buffer);
+    return buffer;
+}
+
+class WrapKeyHeader {
+    kid: string;
+    enc: string;
+    ePubKey: string;
+
+    constructor(kid: string, enc: string, ePubKey: string) {
+        this.kid = kid;
+        this.enc = enc;
+        this.ePubKey = ePubKey;
+    }
+}
+
+class WrapKey {
+    header: WrapKeyHeader;
+    nonce: ArrayBuffer;
+    encryptedData: ArrayBuffer;
+
+    constructor(
+        header: WrapKeyHeader,
+        nonce: ArrayBuffer,
+        encryptedData: ArrayBuffer,
+    ) {
+        this.header = header;
+        this.nonce = nonce;
+        this.encryptedData = encryptedData;
+    }
+
+    toString(): string {
+        const headerJson = JSON.stringify(this.header);
+        return `WK:${encodeBase64Url(new TextEncoder().encode(headerJson))}.${
+            encodeBase64Url(this.nonce)
+        }.${encodeBase64Url(this.encryptedData)}`;
+    }
+}
+
+function concatUint8Array(a: Uint8Array, b: Uint8Array): Uint8Array {
+    const merge = new Uint8Array(a.byteLength + b.byteLength);
+    merge.set(a, 0);
+    merge.set(b, a.byteLength);
+    return merge;
+}
+
+export async function encryptEcdhP256(
+    kid: string,
+    publicKeyPointHex: string,
+    data: ArrayBuffer,
+) {
+    const ENC_AES256_GCM_P256 = "aes256-gcm-p256";
+    const ecdh = Ecdh.fromHex(publicKeyPointHex);
+    const ecdhEphemeral = ecdh.ecdh();
+    const key = await simpleKdf256(ecdhEphemeral.sharedSecret);
+    const nonce = randomNonce();
+
+    const derPrefix = decodeHex(
+        "3059301306072a8648ce3d020106082a8648ce3d030107034200",
+    );
+    const der = concatUint8Array(derPrefix, ecdhEphemeral.ePublicKey);
+    const wrapkeyHeader = new WrapKeyHeader(
+        kid,
+        ENC_AES256_GCM_P256,
+        encodeBase64Url(der),
+    );
+    const cryptoKey = await crypto.subtle.importKey(
+        "raw",
+        key,
+        "AES-GCM",
+        false,
+        ["encrypt"],
+    );
+    const encryptedData = await crypto.subtle.encrypt(
+        { name: "AES-GCM", iv: nonce },
+        cryptoKey,
+        data,
+    );
+    return new WrapKey(wrapkeyHeader, nonce, encryptedData);
+}