In this setup the Satochip only stores the private key, or it also does the signing?
Wrote a quick guide about using an initialized Satochip smart card with Sparrow Wallet: https://github.com/openoms/bitcoin-tutorials/tree/master/satochip#get-started-with-satochip
As these javacards are essentially $5 hardware wallets (with no screen, but using a Secure Element) are great to give bitcoin in a physical form.
This short guide is for the ones receiving them.
To initialize the cards one could use TailsOS offline with Sparrow Wallet or Electrum or a modded version of Seedsigner: nevent1qvzqqqqqqypzp2kq0k2s388x4hcghy2k6s7p5j44jnrpxzmaevfwcxvsprzcrx30qyw8wumn8ghj7mn0wd68ytngw4eh5mmwv4nhjtnhdaexcep0qy38wumn8ghj7mt4d36xjurvv4ux2u3wdp6hx7n0dejkw7fwwahhymry9uqzpaca0y00n4qs4k5drhwaz99vuy78r6ddqxu7hwxy8xghj45knkh5jgfqlz
Discussion
It does store the private key and does the signing also.
It only not capable of generating the seed itself so that is needed to be loaded once from an external source using Sparrow Wallet, Electrum Wallet or the modded Seedsigner.
Once the seed is in the card it cannot be exported and the signing is protected by a 4-16 character PIN.
I assume the JavaCard has to be initialized with bitcoin-specific software (for signing). I wonder which step does that? Or is that not covered by this guide?
Loading the Satochip java applet to the javacard is what I refer to as the DIY version of Satochip. It takes seconds to prepare them. Here are my notes, follow the links and readmes in the linked repos for more details: https://gist.github.com/openoms/510b2876cab19e15c4190456ea8aad82#file-satochip-javacard-applet-install
OK, got it, thx for the clarification! Cool stuff!