What happens if I use the wrong passphrase to decrypt?

With GCM mode, decryption fails with an authentication tag mismatch — you get an error, not garbage text. This is why GCM is preferred over CBC: it detects tampering and wrong keys immediately.

Is the IV safe to store alongside the ciphertext?

Yes. The IV (or nonce) is not secret — it only needs to be unique per encryption with the same key. Storing it with the ciphertext is standard practice. Only the key/passphrase must be kept secret.

TASK

Encrypt text with AES and decrypt it back

Symmetrically encrypt a message with a passphrase using AES-256-GCM, then decrypt the ciphertext with the same key to recover the original.

1

AES is the standard symmetric cipher: the same key encrypts and decrypts. GCM mode provides authenticated encryption — it detects tampering of the ciphertext. Never use ECB or unauthenticated CBC for new data.
2

AES Encryptor →
Enter the plaintext and a passphrase. The tool derives a key (PBKDF2), generates a random IV, and outputs ciphertext + IV + salt, typically Base64-encoded.
3

AES Decryptor →
Paste the ciphertext output and the same passphrase. The tool recovers the original plaintext. If the passphrase is wrong, GCM mode fails with an authentication error rather than returning garbage.
4

Store the passphrase separately from the ciphertext. The IV and salt are not secret and travel with the ciphertext — only the passphrase needs protection.

Frequently asked questions

What happens if I use the wrong passphrase to decrypt?: With GCM mode, decryption fails with an authentication tag mismatch — you get an error, not garbage text. This is why GCM is preferred over CBC: it detects tampering and wrong keys immediately.
Is the IV safe to store alongside the ciphertext?: Yes. The IV (or nonce) is not secret — it only needs to be unique per encryption with the same key. Storing it with the ciphertext is standard practice. Only the key/passphrase must be kept secret.