fix(ext/crypto): deriveBits for ECDH not taking length into account

cli/tests/unit/webcrypto_test.ts

@@ -541,6 +541,71 @@ Deno.test(async function testHkdfDeriveBitsWithLargeKeySize() {
   );
 });
 
+Deno.test(async function testEcdhDeriveBitsWithShorterLength() {
+  const keypair = await crypto.subtle.generateKey(
+    {
+      name: "ECDH",
+      namedCurve: "P-384",
+    },
+    true,
+    ["deriveBits", "deriveKey"],
+  );
+  const result = await crypto.subtle.deriveBits(
+    {
+      name: "ECDH",
+      public: keypair.publicKey,
+    },
+    keypair.privateKey,
+    256,
+  );
+  assertEquals(result.byteLength * 8, 256);
+});
+
+Deno.test(async function testEcdhDeriveBitsWithLongerLength() {
+  const keypair = await crypto.subtle.generateKey(
+    {
+      name: "ECDH",
+      namedCurve: "P-384",
+    },
+    true,
+    ["deriveBits", "deriveKey"],
+  );
+  await assertRejects(
+    () =>
+      crypto.subtle.deriveBits(
+        {
+          name: "ECDH",
+          public: keypair.publicKey,
+        },
+        keypair.privateKey,
+        512,
+      ),
+    DOMException,
+    "Invalid length",
+  );
+});
+
+Deno.test(async function testEcdhDeriveBitsWithNullLength() {
+  const keypair = await crypto.subtle.generateKey(
+    {
+      name: "ECDH",
+      namedCurve: "P-384",
+    },
+    true,
+    ["deriveBits", "deriveKey"],
+  );
+  const result = await crypto.subtle.deriveBits(
+    {
+      name: "ECDH",
+      public: keypair.publicKey,
+    },
+    keypair.privateKey,
+    // @ts-ignore: necessary until .d.ts file allows passing null (see https://github.com/microsoft/TypeScript-DOM-lib-generator/pull/1416)
+    null,
+  );
+  assertEquals(result.byteLength * 8, 384);
+});
+
 Deno.test(async function testDeriveKey() {
   // Test deriveKey
   const rawKey = await crypto.getRandomValues(new Uint8Array(16));

ext/crypto/00_crypto.js

@@ -1073,7 +1073,7 @@
     /**
      * @param {AlgorithmIdentifier} algorithm
      * @param {CryptoKey} baseKey
-     * @param {number} length
+     * @param {number | null} length
      * @returns {Promise<ArrayBuffer>}
      */
     async deriveBits(algorithm, baseKey, length) {
@@ -1088,10 +1088,12 @@
         prefix,
         context: "Argument 2",
       });
-      length = webidl.converters["unsigned long"](length, {
-        prefix,
-        context: "Argument 3",
-      });
+      if (length !== null) {
+        length = webidl.converters["unsigned long"](length, {
+          prefix,
+          context: "Argument 3",
+        });
+      }
 
       // 2.
       const normalizedAlgorithm = normalizeAlgorithm(algorithm, "deriveBits");
@@ -4326,7 +4328,17 @@
             length,
           });
 
-          return buf.buffer;
+          // 8.
+          if (length === null) {
+            return buf.buffer;
+          }
+          if (
+            length === 0 || buf.buffer.byteLength * 8 < length ||
+            length % 8 !== 0
+          ) {
+            throw new DOMException("Invalid length", "OperationError");
+          }
+          return buf.buffer.slice(0, length / 8);
         } else {
           throw new DOMException("Not implemented", "NotSupportedError");
         }