URL payload format.

A CLAIMA claim link looks like this:

https://claima.fun/c#<base64url(JSON_payload)>

The part after # is the URL fragment. By spec, browsers do not transmit the fragment to the server in the request line — so the encrypted blob stays on the receiver's device.

Before base64url encoding, the payload is JSON with these fields:

{
  "v":       2,
  "pk":      "8xJA…q9Rk",        // temp vault pubkey (base58)
  "lamports": 50_000_000,        // amount funded into the vault
  "network": "mainnet-beta",     // or "devnet"
  "salt":    "<base64url>",      // 16 bytes, PBKDF2 salt
  "iv":      "<base64url>",      // 12 bytes, AES-GCM IV
  "ct":      "<base64url>"       // ciphertext + 16-byte auth tag
}

The ct field encrypts a nested JSON envelope. After decryption you get:

{
  "sk":   "<hex>",          // 64-byte ed25519 secret key, hex-encoded
  "note": "happy birthday"  // optional, omitted if absent
}

• base64url means standard base64 with + → -, / → _, and no = padding. URL-safe by definition.
• Strings are UTF-8 byte sequences. The JSON is serialized with JSON.stringify (no pretty-print).
• All sizes are fixed except note and lamports. A typical link is ~260–320 characters of base64url after the #.

To inspect a link manually in a JS console:

const frag = location.hash.slice(1);
const b64u = (s) => s.replace(/-/g, "+").replace(/_/g, "/")
                     + "=".repeat((4 - s.length % 4) % 4);
const json = atob(b64u(frag));
console.log(JSON.parse(json));
// { v: 2, pk: "8xJA…", lamports: 50000000, network: "devnet", salt: "…", iv: "…", ct: "…" }

You can read all of these fields without the password. The ciphertext is opaque until you derive the AES key from the password and decrypt — see how it works for the full recipe.

The v field at the top of the payload is a version number. v1 (deprecated) used a plaintext note field — links of that vintage are rejected with a friendly error and the sender is asked to regenerate. v2 is the current format and encrypts the note inside ct.

Future versions will continue to be additive — readers should check v first and fall through to the newest known schema.