Decrypt a message
ciphertext = (ciphertext from AES-GCM Encrypt)key = (key from AES-GCM Encrypt)nonce = (nonce from AES-GCM Encrypt)tag = (tag from AES-GCM Encrypt)
Result: The original plaintext, or an authentication error.
AES-GCM Decrypt
Decrypt ciphertext encrypted with AES-256-GCM. Requires the correct key, nonce, and authentication tag. If the ciphertext has been tampered with or the wrong key is used, decryption fails with a clear error. This is the counterpart to AES-GCM Encrypt.
Privacy: this tool processes your data entirely in your browser. Nothing you paste or type is sent to the server.
Enter your values and press Calculate — the result appears here.
Worked examples
Frequently asked questions
What happens if I use the wrong key?
Decryption fails with "Authentication failed" - you get no partial results. AES-GCM is designed so that wrong keys produce completely random-looking output that fails the authentication check.
What happens if the ciphertext is tampered with?
Decryption fails. The authentication tag detects any modification to the ciphertext, nonce, or AAD. This is the "authenticated" part of AES-GCM.
Can I decrypt without the nonce?
No. The nonce is required for AES-GCM decryption. Without it, the decryption algorithm cannot proceed. Always store the nonce alongside the ciphertext.
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Decrypt AES-256-GCM ciphertext with authentication verification.
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