BlockchainCards

All your membership cards. One wallet. Nobody else holds the key.

It is what it is.You connect with your wallet,and you can upload and manage your membership cards on solana blockchain.When you press save the site will interact with the smartcontract (the only fee + the blockchain fee) and will encrypt and save your cards in the blockchain. Keep every loyalty, gym and membership card in one place, then open any of them from your watch/phone with a tap.

Why it is safe

Your cards are locked on your device before they go anywhere, using a key made from your own wallet. What is stored online is fully encrypted data that looks like nonsense, and only you and the watch/phone you approve can decrypt it. There is no account, no password and no company database to be breached, because this site never hold your key and never see your cards. Just you should be responsible with your wallet.

Useful information for geeks

• Web ↔ wallet. You sign one fixed message. It is free and sends nothing. Solana wallets sign with Ed25519 (a modern signature scheme) and it is deterministic (the same wallet and message always give the same signature), so any device can rebuild your key. The key-encryption key, or KEK (a master key whose only job is to lock other keys), is the HMAC-SHA256 of that signature (a keyed fingerprint function that turns the signature into a key nobody can guess). It exists only in this tab's memory.
• Web ↔ blockchain. Each card is encrypted in your browser with a random 256-bit data key, using AES-128-CBC (the standard AES cipher, which scrambles data in 16-byte blocks that are chained together) and a fresh random IV (a random starting value, so two identical cards never look alike). An HMAC-SHA256 tag (a tamper seal) is added after encrypting, which is called encrypt-then-MAC (MAC means message authentication code). It is the safest order: changed data is rejected before anything is decrypted. The data key is itself wrapped (encrypted) with your KEK. Solana stores only ciphertext (the scrambled result). The number of cards and their sizes are public.
• Phone wallets. With a wallet on your phone, the page and the wallet app talk through WalletConnect's relay server (run by Reown). Messages are encrypted end to end, so the relay passes them on without being able to read them, and the page checks that every signature really comes from your wallet's address.
• Watch. Pairing uses an ephemeral ECDH key exchange on P-256 (each side makes a one-time key pair and swaps the public halves, so both can work out the same secret without ever sending it). The page encrypts the data key to your watch's own public key, so only that watch can open it. The watch then downloads your cards and decrypts them itself.
• No middleman. The site is static (plain files, no server code of ours), and the files are not minified (not squeezed into unreadable form), so you can read exactly what runs in your browser (press F12).

Get the most out of it

Buy prepaid saves once, then use your first save to add all your cards together. One save covers any number of changes, so the rest will last you for the big updates in the years ahead.

Lost a device? Remove it from your paired devices. Your cards get a new key that only the devices you keep receive, so the lost one can't read anything you save from then on. It still shows the cards it already saved, so for a card that matters, ask the shop for a new number.