What this text encryption tool does
This page turns a piece of text into something unreadable and back again. It offers four methods in the Algorithm menu, and they are not equal: AES-256-GCM is real password-based encryption, while Base64, ROT13 and the Caesar Cipher are encodings or classroom ciphers that anyone can reverse without a secret. Typical uses are protecting a short note before pasting it into a chat or document, sharing a snippet that should only open with an agreed password, checking what a Base64 string contains, or showing students how a shift cipher works.
How to use it
- Pick Encrypt or Decrypt with the two tabs at the top of the card.
- Choose an entry in Algorithm. The password field only appears for AES-256-GCM; the Shift Amount field only appears for the Caesar Cipher.
- Type or paste your text into Input Text. For decryption, paste the exact Base64 string that the tool produced earlier.
- Press the large Encrypt/Decrypt button. The result shows in Output; use Copy to put it on the clipboard.
- Swap moves the output into the input box and flips the mode, which is a quick way to test that a round trip gives back your original text. Clear empties the text, the password and the result.
How each method works
AES-256-GCM with a password
The page calls crypto.subtle, the Web Crypto API built into modern browsers. Your password is stretched into a 256-bit AES key with PBKDF2 using SHA-256, 100,000 iterations and a fresh random 16-byte salt. A random 12-byte initialisation vector is generated, the text is encrypted with AES in Galois/Counter Mode, and the page outputs one Base64 string made of salt + IV + ciphertext (the ciphertext includes GCM's 16-byte authentication tag). Because the salt and IV are random, encrypting the same text twice gives two different results, and both decrypt correctly. GCM also detects tampering: if a single character of the ciphertext changes, or the password is wrong, decryption is rejected with an error instead of producing garbage.
Base64, ROT13 and Caesar
Base64 here first converts your text to UTF-8, so accented letters, Chinese characters and emoji survive the round trip. ROT13 rotates each Latin letter by 13 places, so the same operation both encodes and decodes. The Caesar option rotates letters A–Z and a–z by the shift you set (values are reduced modulo 26) and reverses the shift in Decrypt mode. Digits, punctuation and non-Latin characters pass through these two ciphers unchanged.
Limits and good practice
The strength of the AES mode depends mostly on your password: a short or common password can still be guessed offline by someone who has the ciphertext, even with 100,000 PBKDF2 rounds. Use a long passphrase and send it through a different channel than the encrypted text. The output format is specific to this page, so other AES tools will usually not open it unless they use the same salt, IV and key-derivation layout. Very large inputs may run into browser memory limits; the tool is meant for text, not files.
There is no password recovery. If the password is lost, the AES output cannot be decrypted by this page or by anyone else.
Frequently asked questions
Is my text or password sent anywhere?
No. Encryption, decoding and copying all run in JavaScript inside your browser tab, and the tool makes no network requests with your input. Nothing is saved to storage either, so closing or reloading the page discards the text and password.
Why do I get a different result every time I encrypt the same text?
Each AES encryption uses a new random salt and IV, which are stored at the start of the output. This is intentional and prevents someone from spotting repeated messages. Any of the outputs decrypts back to the same text with the right password.
Decryption failed – what went wrong?
For AES, the password must match exactly, including case and spaces, and the Base64 string must be complete. A missing or altered character, a truncated copy or a wrong password all make the authentication check fail. For Base64, the error means the input is not valid Base64.
Is Base64 a form of encryption?
No. Base64 only changes how bytes are written so they fit in plain text. Anyone can decode it without a key, and ROT13 or a Caesar shift is just as easy to undo. Use the AES-256-GCM option when the content actually needs to stay private.
Can I encrypt files or images?
Not with this page. It reads and writes text only. For files, use dedicated software that supports authenticated encryption, such as an encrypted archive or disk-encryption tool.