The SPL Memo program, payment references from Solana Pay, invoice ids, and custom instruction data are stored unencrypted in the ledger. Exchanges and merchants often require a memo or reference that maps directly to your account with them. Once one such memo sits next to your vault, the vault is tied to your identity at that service.

Anything a dApp writes into a memo or instruction is public forever.

Memos and instruction data are plaintext

WebAuthn only hands you the public key at creation time, which makes it look private. It isn't. ECDSA allows public key recovery: from one signature and the signed bytes you get at most two candidate keys, and a second signature leaves exactly one. Combined with the vault derivation, a single leaked assertion can reveal your vault. On Solana the key is in the instruction anyway. This matters for assertions you send off-chain, for example to a backend for login, or to a relayer before submission.

One signature plus its message is enough to recover the passkey's public key.

Signatures reveal the public key

Every Solana account must hold a rent-exempt minimum of lamports. The first transaction that creates your vault PDA, and each ATA after it, transfers that SOL from a payer account. If that payer is your exchange withdrawal address or your old wallet, the new vault is linked to it from the moment it exists. The same happens in reverse when you close accounts: the rent refund goes to a destination you choose, which links the closed account to that destination.

Creating a vault and its token accounts needs rent-exempt SOL from somewhere.