grafana/k6 · error

unsupported algorithm: %v

Error message

unsupported algorithm: %v

What it means

Thrown inside k6 WebCrypto's JWK export path when a key's algorithm object implements neither the hasHash interface (HMAC-style, providing a hash name) nor hasAlg (AES-style, providing the algorithm name). extractAlg (internal/js/modules/k6/webcrypto/jwk.go:92-109) type-switches on inAlg and its default branch returns this error, printing the offending value with %v. Like 1117 it surfaces to scripts as 'failed to extract algorithm: unsupported algorithm: ...' from exportKey('jwk', ...).

Source

Thrown at internal/js/modules/k6/webcrypto/jwk.go:108

}

func extractAlg(inAlg any, keyLen int) (string, error) {
	switch alg := inAlg.(type) {
	case hasHash:
		v := alg.hash()
		if len(v) < 4 {
			return "", errors.New("length of hash algorithm is less than 4: " + v)
		}
		return "HS" + v[4:], nil
	case hasAlg:
		v := alg.alg()
		if len(v) < 4 {
			return "", errors.New("length of named algorithm is less than 4: " + v)
		}

		return fmt.Sprintf("A%d%s", (8 * keyLen), v[4:]), nil
	default:
		return "", fmt.Errorf("unsupported algorithm: %v", inAlg)
	}
}

// ecJWK represents an EC JWK key.
// It is used to unmarshal ECDSA and ECDH keys to and from JWK format.
type ecJWK struct {
	// Key type
	Kty string `json:"kty"`
	// Canonical Curve
	Crv string `json:"crv"`
	// X coordinate
	X string `json:"x"`
	// Y coordinate
	Y string `json:"y"`
	// Private scalar
	D string `json:"d"`
}

View on GitHub (pinned to 93accf6570)

Solutions

1. Export the key as 'raw' instead of 'jwk' — the raw path does not consult extractAlg.
2. Recreate the key via generateKey/importKey so its algorithm object is one of the standard types.
3. If maintaining a k6 extension, ensure symmetric CryptoKeys get KeyAlgorithm values that implement hasAlg (AES) or hasHash (HMAC).

Example fix

// before
const jwk = await crypto.subtle.exportKey('jwk', key); // unsupported algorithm: ...

// after
const raw = await crypto.subtle.exportKey('raw', key);

try {
  await crypto.subtle.exportKey('jwk', key);
} catch (e) {
  if (/unsupported algorithm/.test(e.message)) { await crypto.subtle.exportKey('raw', key); /* proceed with raw bytes */ } else throw e;
}

When it happens

Trigger: exportSymmetricJWK invoked with a key whose handle is a []byte but whose Algorithm is an unexpected Go type (e.g. an EC or RSA algorithm struct attached to a byte-slice handle) — a state normal API flows cannot produce; it indicates a mismatched/corrupted CryptoKey rather than a user-input error.

Common situations: Practically unseen in stock k6; would appear in forks/extensions that construct CryptoKey values manually or reuse the webcrypto package's internals with nonstandard algorithm types.

Related errors

• failed to extract algorithm: %w
• curve not supported for converting to ECDSA key
• invalid block size
• unsupported algorithm {alg}
• key (k) is required

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/8812f040fc75ef74. Report an issue: GitHub.