AES‑256‑GCM cipher online – encoder/decoder
AES-256-GCM encryptor and decryptor online with a password-derived key (PBKDF2, 600,000 iterations). Everything runs locally in your browser.
How are messages really protected today?
What is AES-256-GCM?
AES-256-GCM is a modern standard for authenticated encryption. It works on bytes rather than alphabet letters, uses a 256-bit key and, besides encrypting the data, produces a tag that detects any later change to the message.
How does a password become a key?
A password cannot be used directly, so the tool passes it through PBKDF2 with SHA-256 and 600,000 iterations, together with a random 16-byte salt. The result is a 256-bit key. The high iteration count deliberately slows down brute-force password guessing.
Why does the same text give a different result?
Every encryption draws a fresh salt and a fresh 12-byte IV, so the same message with the same password looks different each time. This is intentional: nobody can tell that two ciphertexts hide identical content.
What does the encrypted result contain?
The output has five parts separated by dots: the format marker RBAES1, the iteration count, the salt, the IV and the ciphertext itself together with a 128-bit authentication tag. The salt and IV are not secret — they must travel with the message so the recipient can rebuild the key.
How do you decrypt a message?
Paste the whole string including the RBAES1 marker and enter the same password. The tool reads the salt and IV, derives the key again and verifies the authentication tag. If the password is wrong, or someone changed a single character of the ciphertext, decryption fails with an error instead of returning corrupted text.
How AES differs from classical ciphers
Caesar or Vigenère rearrange alphabet letters and preserve the structure of the language. AES works on bytes, mixes the data across many rounds and produces output indistinguishable from random. The other key difference is GCM: classical ciphers have no idea whether a message was swapped on the way.
See also: Caesar cipher · Vigenère cipher
How do you choose a password?
The security of the whole operation comes down to the password — the tool requires at least 12 characters, yet short and common passwords remain the weakest link. A long random passphrase from a password manager works best. Send the password to the recipient through a different channel than the ciphertext, and never attach it to a shared link.
Can AES-256 be broken?
No practical attacks on the algorithm itself are known; searching the space of 256-bit keys is beyond current and foreseeable technology. In practice it is not the cipher that gets broken but its surroundings: a weak password, an infected device, a careless channel for sharing the password, or a copy of the plaintext saved somewhere.
History of AES and the GCM mode
The Rijndael algorithm, designed by Joan Daemen and Vincent Rijmen, won an open competition run by the US NIST and was announced as the AES standard in 2001. The GCM mode was later developed by David McGrew and John Viega and approved by NIST in 2007, combining fast encryption with detection of modified data.