[aussedatlo]

📝 Description

Get extended public key for signer-btc-legacy (ticket 1.3 of Plan: Bitcoin family on DMK). Stacked on #1994.

• getExtendedPublicKey(path, { skipOpenApp }) returns { extendedPublicKey }, named like signer-btc's method.
• The legacy protocol has no xpub command, so a task does what hw-app-btc's BtcOld.getWalletXpub does: two get address calls (the parent's key for the fingerprint, the account's key and chain code), then the BIP32 serialization with the coin's version, base58check encoded. A path with fewer than two levels returns an error before any APDU.
• LegacyCoinProfile gets xpubVersion; LITECOIN_PROFILE uses 0x019da462 ("Ltub"), the value Ledger Wallet reads from coin-bitcoin's networks.ts.
• New dependencies: @noble/hashes (as in signer-zcash) and bs58 (workspace catalog).

const { observable } = signer.getExtendedPublicKey("84'/2'/0'");

One deliberate difference with hw-app-btc: it always sets the hardened bit of the child index; the kit writes the real index. Both are identical for account paths, the only ones Ledger Wallet uses.

Compared with Ledger Wallet. For the 44', 49' and 84' Litecoin accounts of the Speculos seed, the same three xpubs come from:

• ledger-live's own hw-app-btc (BtcOld.getWalletXpub, Ledger Wallet's Litecoin xpubVersion), run live against a real Speculos Litecoin app through the mock server;
• an off-device BIP32 derivation of the seed, checked against the BIP32 test vector;
• the kit, in its unit test (fed the app's answers) and in the e2e tests.

Sample app: a "Get extended public key" action on the Litecoin screen, and 3 Playwright specs against the real Litecoin app 2.4.13 on Flex 1.7.0, through the mock server and Speculos.

❓ Context

• JIRA or GitHub link: DSDK-1617
• Feature: Legacy Bitcoin signer kit, wallet xpub

✅ Checklist

Pull Requests must pass CI checks and undergo code review. Set the PR as Draft if it is not yet ready for review.

• Covered by automatic tests
• Changeset is provided
• Documentation is up-to-date
• Impact of the changes:
  • signer-btc-legacy: new get extended public key API; xpubVersion is a new required field of LegacyCoinProfile
  • Sample app: new action on the Litecoin screen; Playwright specs in signers/litecoin (3 new specs, all on real Speculos)

---

🧐 Checklist for the PR Reviewers

• The code aligns with the requirements described in the linked JIRA or GitHub issue.
• The PR description clearly documents the changes made and explains any technical trade-offs or design decisions.
• There are no undocumented trade-offs, technical debt, or maintainability issues.
• The PR has been tested thoroughly, and any potential edge cases have been considered and handled.
• Any new dependencies have been justified and documented.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
device-sdk-ts-sample	Ready	Preview	Oct 23, 2026 10:18am UTC
doc-device-management-kit	Ready	Preview	Oct 23, 2026 10:18am UTC

[github-actions]

Danger Check Results

Messages

✅	Danger: All checks passed successfully! 🎉

Generated by 🚫 dangerJS against 3c3018d

[Copilot]

🟡 Changes recommended

Short-path validation runs after app opening, allowing invalid requests to trigger device communication before returning an error.

1 open issue

• Validate key path depth before opening the app · New

1 file not reviewed

• pnpm-lock.yaml: Generated file

What changed in this PR

Adds extended public key retrieval to the legacy Bitcoin signer, building on its existing address API and Litecoin profile.

Changes:

• Adds getExtendedPublicKey and constructs BIP32 keys from parent and account public keys.
• Introduces coin-specific xpub versions and hashing/Base58 dependencies.
• Adds unit coverage, three Litecoin end-to-end cases, documentation, and a sample-app action.

File	Description
pnpm-lock.yaml	Locks hashing and Base58 dependencies.
packages/​signer/​signer-btc-legacy/​src/​internal/​use-cases/​address/​GetExtendedPublicKeyUseCase.ts	Forwards xpub requests and options.
packages/​signer/​signer-btc-legacy/​src/​internal/​use-cases/​address/​GetExtendedPublicKeyUseCase.test.ts	Tests option forwarding and defaults.
packages/​signer/​signer-btc-legacy/​src/​internal/​DefaultSignerBtcLegacy.ts	Implements the signer method.
packages/​signer/​signer-btc-legacy/​src/​internal/​DefaultSignerBtcLegacy.test.ts	Tests signer action wiring.
packages/​signer/​signer-btc-legacy/​src/​internal/​btcLegacyTypes.ts	Adds the dependency-injection identifier.
packages/​signer/​signer-btc-legacy/​src/​internal/​btcLegacyModule.ts	Registers the new use case.
packages/​signer/​signer-btc-legacy/​src/​internal/​btcLegacyModule.test.ts	Tests use-case registration.
packages/​signer/​signer-btc-legacy/​src/​internal/​app-binder/​task/​utils/​legacyTransactionUtils.ts	Adds public-key compression and hashing.
packages/​signer/​signer-btc-legacy/​src/​internal/​app-binder/​task/​GetExtendedPublicKeyTask.ts	Retrieves keys and serializes the xpub.
packages/​signer/​signer-btc-legacy/​src/​internal/​app-binder/​task/​GetExtendedPublicKeyTask.test.ts	Tests serialization and error handling.
packages/​signer/​signer-btc-legacy/​src/​internal/​app-binder/​BtcLegacyAppBinder.ts	Runs the task in the selected app.
packages/​signer/​signer-btc-legacy/​src/​internal/​app-binder/​BtcLegacyAppBinder.test.ts	Tests task-action configuration.
packages/​signer/​signer-btc-legacy/​src/​api/​SignerBtcLegacy.ts	Declares the public method.
packages/​signer/​signer-btc-legacy/​src/​api/​profiles/​litecoinProfile.ts	Sets Litecoin’s Ltub version.
packages/​signer/​signer-btc-legacy/​src/​api/​model/​LegacyCoinProfile.ts	Requires a coin-specific xpub version.
packages/​signer/​signer-btc-legacy/​src/​api/​model/​ExtendedPublicKeyOptions.ts	Defines the app-opening option.
packages/​signer/​signer-btc-legacy/​src/​api/​index.ts	Exports the new public types.
packages/​signer/​signer-btc-legacy/​src/​api/​app-binder/​GetExtendedPublicKeyDeviceActionTypes.ts	Defines action output, errors, and interaction types.
packages/​signer/​signer-btc-legacy/​README.md	Documents xpub usage and options.
packages/​signer/​signer-btc-legacy/​package.json	Adds hashing and Base58 dependencies.
apps/​sample/​src/​components/​SignerLitecoinView/​index.tsx	Adds the xpub action form.
apps/​sample/​playwright/​utils/​drivers/​LtcSignerDriver.ts	Adds xpub form automation.
apps/​sample/​playwright/​cases/​signers/​litecoin/​get-extended-public-key.spec.ts	Checks three Litecoin account xpubs.
.changeset/​bitcoin-legacy-xpub.md	Records the minor package update.

_{Review effort: Balanced}

[Copilot]

🟡 Changes recommended

Address the critical compressed-key handling defect, correct the pre-APDU validation error type, and resolve the LegacyCoinProfile compatibility or release-versioning issue.

2 open issues

• Handle compressed keys correctly when composing legacy xpubs · New
• Validate key path depth before opening the app

1 file not reviewed

• pnpm-lock.yaml: Generated file

_{Review effort: Lite}

[Copilot]

🔵 Needs a closer look

Invalid or empty derivation paths can throw synchronously instead of returning the documented observable error; path validation should handle these inputs and include a regression test.

1 open issue

• Handle compressed keys correctly when composing legacy xpubs

1 resolved since last review

• Validate key path depth before opening the app

1 file not reviewed

• pnpm-lock.yaml: Generated file

_{Review effort: Lite}

[Copilot]

🟢 Approval recommended

No unresolved review comments were identified, and the reviewed changes are assessed as approval-ready.

1 open issue

• Handle compressed keys correctly when composing legacy xpubs

1 file not reviewed

• pnpm-lock.yaml: Generated file

_{Review effort: Lite}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud