Quick start 01 — Install applets on DIY JavaCards

This guide takes a blank JavaCard (for example a J3H145) and flashes the SeedKeeper applet so SeedSigner can store seeds on it. The same steps install Satochip, Satodime, Keycard, Specter-DIY and SmartPGP — only the .cap file changes.

Read Bundled JavaCard Applets first if you are unsure which applet to install. For SeedKeeper you almost certainly want SeedKeeper-0.2-official.cap (plain) or SeedKeeper-Ndef-v0.2-0.1.cap (adds NFC tag behaviour).

What you need

  • A blank or wiped JavaCard.
  • A smart card reader connected to SeedSigner. A USB contact reader is the most reliable choice for flashing; NFC/contactless flashing can be less reliable.
  • Smartcard support enabled (Settings → Advanced; enabled by default).

Steps

  1. Put the card on the reader.

  2. Go to Tools → Smartcard Tools → DIY Tools.

    DIY Tools

  3. Choose Install Applet.

  4. Pick the applet:

    • SeedKeeper-0.2-official.cap — normal SeedKeeper.
    • SeedKeeper-Ndef-v0.2-0.1.cap — SeedKeeper plus NDEF (tap-to-open-app).

  5. If you picked a SeedKeeper build, choose the storage size. 8 KB is the default and is plenty for most users:

    Size Notes
    4 KB Only if you must; very few secrets
    8 KB Recommended default
    16 / 32 / 64 KB For many seeds/descriptors
  6. Wait for the success screen. The card now has the applet.

Verify the applet

  1. Go to Tools → Smartcard Tools → SeedKeeper Functions → Card Settings → Card Info.

    Card Info

  2. Confirm the Type is SeedKeeper and the Version is 0.2-0.1.

    Both applet v0.1 and v0.2 report applet version 0.1. The protocol minor version is the real discriminator (v0.1 → 0.1, v0.2 → 0.2). If you see 0.1, you flashed the legacy v0.1 build.

First use: set a PIN

The first SeedKeeper operation asks you to set a New Card PIN (entered twice). Keep it safe — there is no PIN recovery.

If something goes wrong

  • “No smartcard detected” — re-seat the card, check the reader, or try the other reader type. On NFC, move the card slower/closer.
  • Install fails on a contactless reader — try a USB contact reader.
  • You locked the card with custom GlobalPlatform keys — see Quick start 06 — First-time DIY card setup.
  • A full SeedKeeper v0.1 cannot be freed by deleting secrets — re-flash the v0.2 applet. See SeedKeeper v0.1.

Released under the MIT License. The SeedSigner OS section is mirrored from the seedsigner-os repository at the pinned release commit.

This site uses Just the Docs, a documentation theme for Jekyll.