AES Encrypt & Decrypt
runs in your browserEncrypt text with AES-GCM and a passphrase, and decrypt it again. Tampering is detected, and everything happens in your browser.
AES-GCM, with the key stretched from your passphrase by 600,000 rounds of PBKDF2. The salt and the initialisation vector are random for every message and travel inside it.
Passphrase
There is no recovery. Lose the passphrase and the message is gone.
Message
Encrypted
about this tool
GCM, not CBC
This uses AES-GCM, which authenticates as well as encrypts. Change one bit of an encrypted message and decryption fails outright.
That is not true of AES-CBC, which many online AES tools still use. With CBC and no separate authentication step, altered ciphertext decrypts to different plain text and nothing tells you it happened. An attacker who cannot read your message may still be able to change it in predictable ways. If a tool offers you a choice of mode with no mention of authentication, that is worth noticing.
What travels with the message
Everything needed to decrypt except the passphrase is packed into the output: a version marker, a random salt, and a random initialisation vector, all in front of the ciphertext. One Base64 string is all the recipient needs.
Both random values are new for every message. Reusing an initialisation vector with the same key is the single mistake that breaks GCM completely, which is why they are generated here rather than derived from anything.
Why it pauses
The passphrase is not used as a key directly. It goes through 600,000 rounds of PBKDF2 first, which is the current recommended floor. That pause of a fraction of a second is the point: it costs you almost nothing once and costs an attacker the same amount for every guess.
When decryption fails
The tool says the passphrase may be wrong, the key size may not match, or the message may have been altered, without choosing between them. That is not vagueness. GCM verifies the whole message as one unit, so a failure genuinely cannot be attributed to a particular cause, and guessing would be misleading.
What this is not
This is a good way to put a note somewhere untrusted, or to hand something to a colleague over a channel you would rather not trust, provided you share the passphrase another way. It is not a replacement for a password manager, for encrypted messaging, or for anything where the consequence of being wrong is serious. There is also no recovery: lose the passphrase and the message is gone for good.