Practical guide and verification
Treat the IV as a uniqueness requirement
AES-GCM relies on a nonce or IV that must not be reused with the same key. Random generation is practical for many browser workflows, but the surrounding system still needs to preserve the generated package and avoid constructing a design that repeats IVs under one key.
Keep authentication and decryption together
GCM is an authenticated-encryption mode: the authentication tag is part of the security property, not an optional checksum. A package should be accepted only after authenticated decryption succeeds; never expose unauthenticated plaintext as though it were valid.
Understand what the passphrase KDF is doing
When a human passphrase is used, the key-derivation function, salt and iteration settings turn that passphrase into an AES key. Those parameters need to travel with the encrypted package so the same key can be derived later without storing the passphrase itself.
Do not confuse local processing with protocol design
Running encryption in the browser can keep plaintext off the WebToolArc server, but it does not decide how recipients exchange passwords, authenticate each other, rotate secrets, back up data or recover from key loss. Those remain application-level responsibilities.
Test round-trip recovery before relying on the package
After encrypting important data, decrypt the generated package in a fresh state and confirm the recovered bytes match the original. A round trip catches copy truncation, formatting mistakes and incompatible parameter handling before the ciphertext becomes the only copy.
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