What is AES?
AES decryption reverses AES encryption, turning ciphertext back into the original plaintext. AES is symmetric, so decryption uses the same secret key as encryption — plus the same mode, padding and initialization vector (IV). If any of these do not match what was used to encrypt, decryption will fail or produce garbage. This tool runs AES decryption entirely in your browser, so your key and data never leave your device.
Match the settings: you must use the same key, mode, padding and IV that were used to encrypt. Decryption runs locally in your browser. See the AES Encryption tool.
How AES works
AES decryption applies the inverse of each encryption step:
- Key expansion — the same secret key is expanded into the round keys.
- Inverse rounds — each block runs through InvShiftRows, InvSubBytes, AddRoundKey and InvMixColumns to undo the mixing.
- Mode & IV — the mode (CBC, GCM, …) and IV are used to chain blocks back to the original plaintext.
- Unpadding — padding (e.g. PKCS7) is removed to recover the exact original data.
How to use
- Paste the AES ciphertext.
- Enter the same key and settings used to encrypt.
- The decrypted text appears in the output.
Options explained
- Key size — Must match the key used to encrypt (128, 192 or 256-bit).
- Mode — Must match (CBC, ECB, CFB, OFB, CTR or GCM).
- IV — Provide the same initialization vector used during encryption.
- Padding — Must match (e.g. PKCS7) so the original length is restored.
Common uses
- Reading AES-encrypted messages and files.
- Recovering encrypted backups and exports.
- Decoding data encrypted by an app or API you control.
Frequently asked questions
Why does decryption fail or give garbage?
Almost always because the key, mode, padding or IV does not exactly match what was used to encrypt.
Do I need the original IV?
Yes, for modes like CBC and GCM. The IV is not secret but must be the same one used to encrypt.
Is my key sent anywhere?
No. Decryption happens entirely in your browser.