InvalidAccessError: Failed to execute 'exportKey' on 'SubtleCrypto': key is not extractable

Chromium's text is above; Safari/WebKit: "The CryptoKey is nonextractable"; Firefox: "A parameter or an operation is not supported by the underlying object". All are `InvalidAccessError` DOMExceptions.

WebCrypto SubtleCrypto.exportKey / wrapKey — DOMException InvalidAccessError (Chromium / Firefox / WebKit)

What it means

The key was created with `extractable: false`, so its material can never be read back — not by `exportKey`, not by `wrapKey`. That is the point of the flag: the private key stays inside the browser's crypto implementation, and script (including injected script) can use it but not steal it. Public keys of a generated pair are always exportable; this error concerns private and secret keys.

Why it happens

• The key was generated non-extractable on purpose

  common

  Libraries and passkey-like designs create device-bound keys this way. A later feature that wants to show, back up or sync the private key collides with that decision.

• A key restored from IndexedDB keeps its flag

  occasional

  CryptoKeys stored in IndexedDB come back exactly as they were created; making them exportable later is impossible.

• A library's default

  occasional

  Some JOSE and E2E libraries generate keys with `extractable: false` by default; their export helpers then fail for private keys.

How to fix it

1. 1.

   Keep the private key as an object, export the public key

   Store non-extractable keys as `CryptoKey` objects in IndexedDB and share only the public key (SPKI or JWK). This keeps the protection the flag provides.

   const pair = await crypto.subtle.generateKey({ name: "ECDSA", namedCurve: "P-256" }, false, ["sign", "verify"]);
   // Persist the non-extractable private key as a CryptoKey object (structured clone), never as bytes:
   await idbPut("signing-key", pair.privateKey);
   // Share only the public key:
   const jwk = await crypto.subtle.exportKey("jwk", pair.publicKey);

2. 2.

   Create extractable keys only when export is a requirement

   If the private key genuinely must leave the browser, generate it extractable and export it only wrapped with another key.

   // Only if the private key must leave the browser (e.g. a user-initiated, encrypted backup):
   const pair = await crypto.subtle.generateKey({ name: "ECDSA", namedCurve: "P-256" }, true, ["sign", "verify"]);
   const wrapped = await crypto.subtle.wrapKey("pkcs8", pair.privateKey, backupKey, { name: "AES-GCM", iv });

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