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 Encryptor

Encrypt text with AES in CTR mode (NIST SP 800-38A, native Web Crypto implementation) — a real algorithm verified byte-for-byte against official NIST test vectors (F.5.1/F.5.3/F.5.5). 128/192/256-bit key, 16-byte IV (the full initial counter block). Free, private, and 100% client-side. Never reuse an IV with the same key.

KeyIV (initialization vector)Output format

Input

Try an example:

Output

Local only

Recent history

No history yet

How to use

Enter your plaintext in the input box.
Set the key (16, 24 or 32 bytes) and the 16-byte IV as UTF-8 text.
Choose hex or base64 output for the ciphertext.
Copy or download the ciphertext.

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)

Related tools

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.

TOOL

AES Encryptor

Encrypt text or binary data with AES (CBC/GCM/ECB) using Web Crypto API. Free, private, and 100% client-side.

TOOL

ChaCha20 Encryptor

Encrypt text with the ChaCha20 stream cipher (RFC 8439) — a real algorithm verified byte-for-byte against official RFC test vectors. 256-bit key (32 bytes), 96-bit nonce (12 bytes), 32-bit block counter. Free, private, and 100% client-side. Never reuse a nonce with the same key.

TOOL