AES-GCM Decrypt

Test the exact key, IV, AAD, ciphertext, tag length, and byte layout behind an authentication failure

Safety note: Keep the AES key secret. The IV is not secret, but it must be unique for each encryption with the same key and must stay paired with the ciphertext.

Decrypt an AES-GCM payloadTest separate or combined payloads with the exact tag length and AAD used by the source system

Load a known-good sample first, then replace one input at a time.

Key length

Key encoding

IV encoding

Payload encoding

Payload layout

AES key

Masked by default; never put a real key in a URL.

An IV can be public; uniqueness under the key is what matters.

Ciphertext

Auth tag

Interoperability settings tag length and optional AAD

Auth tag length

AAD encoding

Additional authenticated data (AAD)

AAD is authenticated but not encrypted. Decryption needs the exact same AAD bytes, encoding, and tag length.

What AES-GCM Needs

AES-GCM authenticates the ciphertext and any optional AAD. Decryption needs the exact key, IV, ciphertext, tag, AAD, and tag length. The page keeps each byte-oriented setting visible so you can reproduce another implementation without guessing its payload format.

Run the AES-GCM Workflow

Choose the encodings and payload layout used by the other implementation.
Paste either separate ciphertext and tag values or one ciphertext || tag payload.
Open Interoperability settings only when you need a non-default tag length or AAD.
If authentication fails, verify every byte-oriented setting rather than changing several inputs at once.

Why AES-GCM Tag Verification Fails

A tag failure does not reveal which input is wrong. Check the byte encoding, IV, ciphertext/tag split, AAD, and tag length before assuming the key is wrong. In a combined payload, this tool treats the final selected tag-length bytes as the tag. A successful decrypt authenticates the complete set of inputs.