Corebytes · Local-only utility

Browser Crypto Lab

Decrypt and authenticate AES-256-GCM data, then digitally sign or verify the ciphertext envelope with ECDSA P-256. All operations use the browser Web Crypto API.

No data leaves this page. Its Content Security Policy blocks network requests, images, forms, and external scripts. Use test keys only; the published fixture key is intentionally non-secret.

AES-256-GCM · Published key

Encrypt fixture

Encrypts UTF-8 plaintext with the published fixture key and no AAD. A fresh random 96-bit nonce is generated for every encryption; the original nonce is reserved for its original ciphertext.

Published key · Base64 · 32 bytes

3jw5pZesXpsKmGrsRJlJpriRXNQL0IhEC1MUW2qMxas=

Plaintext · UTF-8

Ready. The resulting nonce, ciphertext, and tag will be copied into the decrypt fixture below.

AES-256-GCM

Decrypt fixture

The authentication tag is checked before plaintext is returned. Any altered key, nonce, ciphertext, tag, or AAD causes failure.

Key · Base64 · 32 bytes Nonce · Base64 · 12 bytes Ciphertext · Base64 Authentication tag · Base64 · 16 bytes Additional authenticated data · UTF-8 · optional

Ready.

Envelope signature

Sign

Generates an ephemeral ECDSA P-256 keypair and signs a canonical envelope containing the algorithm, nonce, ciphertext, tag, and AAD—but never the AES key.

Public key · JWK Signature · Base64 No signing key generated.

Signature verification

Verify

Verifies the displayed signature against the current ciphertext envelope. Changing any signed field should make verification fail.

Ready.