Keeping cryptocurrency spending keys safe and being able to use them when signing a transaction is a well-known problem, addressed by hardware wallets. Our work focuses on a transaction signing process for privacy-centric cryptocurrency Monero, in the hardware wallets. We designed, implemented, and analyzed a privacy-preserving transaction signing protocol that runs on a hardware wallet and protects the spending keys. Moreover, we also implemented a privacy-preserving multi-party version of the Bulletproof zero-knowledge prover algorithm, which runs on a hardware wallet with constant memory. We present the protocols and evaluate their performance on a real hardware wallet.