Encrypt with CTR
plaintext = Hello, World!
Result: Ciphertext and nonce. ⚠️ No authentication tag - ciphertext can be tampered with undetected.
AES-CTR Demonstration
⚠️ EDUCATIONAL DEMONSTRATION - Do not use AES-CTR for new applications. This tool demonstrates how AES-CTR (Counter mode) works and why AES-GCM (authenticated encryption) is preferred. CTR mode converts a block cipher into a stream cipher, providing confidentiality but NOT authentication. Use AES-GCM for production encryption.
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 is CTR mode?
CTR (Counter) mode converts a block cipher into a stream cipher. It encrypts a counter value and XORs the result with the plaintext. This allows encryption of arbitrary-length data without padding. However, it provides NO authentication.
Why is CTR not recommended?
AES-CTR is vulnerable to: (1) Ciphertext malleability - XOR-based construction allows bit-flipping attacks. (2) No authentication - tampering is undetected. (3) Nonce reuse is catastrophic - reusing a nonce with the same key reveals the XOR of two plaintexts.
What is the difference between CTR and GCM?
CTR is the underlying counter mode; GCM adds Galois Message Authentication Code (GMAC) on top. GCM = CTR + authentication. Always prefer GCM - it provides both confidentiality and integrity.
Should I use this in production?
No. This is an educational demonstration. For production encryption, use AES-GCM. If you must use CTR, add HMAC-SHA256 for authentication (Encrypt-then-MAC).
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