Is my data uploaded anywhere?

No. All processing happens locally in your browser with no server round-trip.

Does this tool work offline?

Yes. Once the page loads, the tool runs entirely client-side and needs no network connection.

Is this real AES-CTR encryption?

Yes. It uses the browser-native Web Crypto AES-CTR implementation with the full 128-bit counter increment (NIST SP 800-38A semantics) and is verified byte-for-byte against the official NIST test vectors F.5.1/F.5.3/F.5.5, cross-checked with OpenSSL.

What key and IV sizes are required?

The key must be 16, 24 or 32 bytes and the IV exactly 16 bytes, entered as UTF-8 text; the IV is the full initial counter block. Other lengths are rejected with an explicit error. Never reuse an IV with the same key.

TOOL

AES-CTR Decryptor

Decrypt AES-CTR ciphertext (NIST SP 800-38A, native Web Crypto implementation) — a real algorithm verified byte-for-byte against official NIST test vectors. Key must be 16, 24 or 32 bytes, IV exactly 16 bytes (the same full initial counter block used for encryption). Ciphertext input format follows the output format option (hex or base64). Free, private, and 100% client-side.

KeyIV (initialization vector)Output format

Input

Try an example:

Output

Local only

Recent history

No history yet

How to use

Paste the AES-CTR ciphertext (hex or base64) into the input box.
Set the same key (16, 24 or 32 bytes) and the same 16-byte IV used for encryption.
Choose the format matching your ciphertext.
Copy the recovered plaintext.

Frequently asked questions

Is my data uploaded anywhere?: No. All processing happens locally in your browser with no server round-trip.
Does this tool work offline?: Yes. Once the page loads, the tool runs entirely client-side and needs no network connection.
Is this real AES-CTR encryption?: Yes. It uses the browser-native Web Crypto AES-CTR implementation with the full 128-bit counter increment (NIST SP 800-38A semantics) and is verified byte-for-byte against the official NIST test vectors F.5.1/F.5.3/F.5.5, cross-checked with OpenSSL.
What key and IV sizes are required?: The key must be 16, 24 or 32 bytes and the IV exactly 16 bytes, entered as UTF-8 text; the IV is the full initial counter block. Other lengths are rejected with an explicit error. Never reuse an IV with the same key.

Glossary terms

CTR (Counter Mode)

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