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crypto: fix webcrypto derive(Bits|Key) resolve values and docs #38148

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crypto: fix webcrypto derive(Bits|Key) resolve values and docs #38148

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4 changes: 2 additions & 2 deletions doc/api/webcrypto.md
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Original file line number Diff line number Diff line change
Expand Up @@ -275,7 +275,7 @@ async function pbkdf2Key(pass, salt, iterations = 1000, length = 256) {
ec.encode(pass),
'PBKDF2',
false,
['deriveBits']);
['deriveKey']);
const key = await subtle.deriveKey({
name: 'PBKDF2',
hash: 'SHA-512',
Expand Down Expand Up @@ -536,7 +536,7 @@ added: v15.0.0
* `derivedKeyAlgorithm`: {HmacKeyGenParams|AesKeyGenParams}
* `extractable`: {boolean}
* `keyUsages`: {string[]} See [Key usages][].
* Returns: {Promise} containing {ArrayBuffer}
* Returns: {Promise} containing {CryptoKey}
<!--lint enable maximum-line-length remark-lint-->

Using the method and parameters specified in `algorithm`, and the keying
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2 changes: 1 addition & 1 deletion lib/internal/crypto/pbkdf2.js
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Expand Up @@ -122,7 +122,7 @@ async function pbkdf2DeriveBits(algorithm, baseKey, length) {
return new Promise((resolve, reject) => {
pbkdf2(raw, salt, iterations, byteLength, hash, (err, result) => {
if (err) return reject(err);
resolve(result);
resolve(result.buffer);
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@tniessen tniessen Apr 8, 2021 •
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Technically, pbkdf2 is only required to give us a Buffer, which does not necessarily have the same byte length as the backing ArrayBuffer:

> Buffer.from([1, 2, 3]).buffer.byteLength
8192
> crypto.randomFillSync(Buffer.allocUnsafe(1024)).buffer.byteLength
8192

That's one of many reasons why WebCrypto doesn't align well with Node.js. However, we know that the implementation of PBKDF2 always returns a Buffer that has the same byteLength as the backing ArrayBuffer. And, hopefully, tests will catch it if that ever changes.

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Yes, i've checked that they do. Alternatively we can do new Uint8Array(result).buffer

> const foo = Buffer.from('foo')
> foo.buffer.byteLength
8192
> new Uint8Array(foo).buffer
ArrayBuffer { [Uint8Contents]: <66 6f 6f>, byteLength: 3 }

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I think these would be places where adding assertions about matching lengths and byteOffsets might make sense :)

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Alternatively we can do new Uint8Array(result).buffer

That would create an unnecessary copy of sensitive data (the result of PBKDF2 is considered secret). And yes, I realize that arguing about memory safety is moot in JavaScript :)

});
});
}
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2 changes: 1 addition & 1 deletion lib/internal/crypto/scrypt.js
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Expand Up @@ -167,7 +167,7 @@ async function scryptDeriveBits(algorithm, baseKey, length) {
return new Promise((resolve, reject) => {
scrypt(raw, salt, byteLength, { N, r, p, maxmem }, (err, result) => {
if (err) return reject(err);
resolve(result);
resolve(result.buffer);
});
});
}
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1 change: 1 addition & 0 deletions test/parallel/test-webcrypto-derivebits-ecdh.js
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Expand Up @@ -98,6 +98,7 @@ async function prepareKeys() {
public: publicKey
}, privateKey, 8 * size);

assert(bits instanceof ArrayBuffer);
assert.strictEqual(Buffer.from(bits).toString('hex'), result);
}

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1 change: 1 addition & 0 deletions test/parallel/test-webcrypto-derivebits-hkdf.js
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Expand Up @@ -237,6 +237,7 @@ async function testDeriveBits(
baseKeys[size],
256);

assert(bits instanceof ArrayBuffer);
assert.strictEqual(
Buffer.from(bits).toString('hex'),
kDerivations[size][saltSize][hash][infoSize]);
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1 change: 1 addition & 0 deletions test/parallel/test-webcrypto-derivebits-node-dh.js
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Expand Up @@ -112,6 +112,7 @@ async function prepareKeys() {
public: publicKey
}, privateKey, null);

assert(bits instanceof ArrayBuffer);
assert.strictEqual(Buffer.from(bits).toString('hex'), result);
}

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1 change: 1 addition & 0 deletions test/parallel/test-webcrypto-derivebits-pbkdf2.js
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Expand Up @@ -421,6 +421,7 @@ async function testDeriveBits(

const bits = await subtle.deriveBits(algorithm, baseKeys[size], 256);

assert(bits instanceof ArrayBuffer);
assert.strictEqual(
Buffer.from(bits).toString('hex'),
kDerivations[size][saltSize][hash][iterations]);
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3 changes: 3 additions & 0 deletions test/parallel/test-webcrypto-derivebits.js
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Expand Up @@ -31,6 +31,8 @@ const { internalBinding } = require('internal/test/binding');
}, alice.privateKey, 128),
]);

assert(secret1 instanceof ArrayBuffer);
assert(secret2 instanceof ArrayBuffer);
assert.deepStrictEqual(secret1, secret2);
}

Expand Down Expand Up @@ -114,6 +116,7 @@ if (typeof internalBinding('crypto').ScryptJob === 'function') {
name: 'NODE-SCRYPT',
salt: ec.encode(salt),
}, key, length);
assert(secret instanceof ArrayBuffer);
assert.strictEqual(Buffer.from(secret).toString('hex'), expected);
}

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