NFCommunicator

Source available on GitHub: https://github.com/AlsatianConsulting/NFCommunicator

NFCommunicator lets you store one encrypted plain-text message on an NFC tag and read it back using a shared password — entirely offline, with no account or cloud service required.

WHAT IT DOES
• Writes an AES-256-GCM encrypted message to any writable NFC tag
• Reads and decrypts the message when the correct password is supplied
• Clears app-owned message data from a tag when you no longer need it
• Supports NDEF tags and raw MIFARE Classic tags on compatible devices

HOW IT WORKS
Write mode: enter a password, confirm it, type your plain-text message, then hold a tag to the phone. The message is encrypted with a fresh random salt and nonce and written to the tag.

Read mode: hold a tag to the phone. If it contains this app's encrypted data, you will be prompted for the password. Enter it and tap Try Password to decrypt.

Clear mode: hold a tag to clear this app's message payload from it without affecting other tag data.

SECURITY AND PRIVACY
• AES-256-GCM encryption with PBKDF2-HMAC-SHA256 key derivation
• Random salt and nonce generated per message — no two ciphertexts are alike
• Password is never stored anywhere on the device
• Decrypted text exists only in memory while it is on screen
• No network permissions — the app makes zero network connections
• No analytics, no ads, no accounts
• FLAG_SECURE prevents decrypted content from appearing in screenshots or the recent-apps thumbnail

TAG COMPATIBILITY
• Standard NDEF read, write, and clear on all compatible tags
• Raw MIFARE Classic 1K/4K read, write, and clear on handsets that expose the low-level interface
• Automatic backend selection — prefers raw MIFARE Classic when available
• Real-time encrypted size estimate before you write, so you know the message fits

USER EXPERIENCE
• Passive NFC detection — just hold a tag to the screen, no button press required
• Character count and per-backend size estimates shown while you type
• Copy-to-clipboard with a 60-second auto-clear to protect decrypted content
• Haptic feedback on card detect, write success, and error
• Clear diagnostic messages for wrong passwords, unrecognized tag formats, tag loss, and unsupported hardware
• Dark orange theme optimized for readability in field conditions

WHO IT IS FOR
• Teams sharing offline credentials, access codes, or instructions on physical NFC tags
• Field workflows where network connectivity is unavailable or untrusted
• Anyone who needs a simple, auditable way to put an encrypted secret on a physical object

REQUIREMENTS
• Android 8.0 (API 26) or later
• Device with NFC support
• Writable NFC tag with sufficient capacity for your message
• A shared password known to both the writer and the reader