Ledger Generic App signing fails due to `spec_name` mismatch

[pilab-dohyeon]

Description

When signing transactions with the Ledger Generic App on chains where the display name (from system_chain RPC) differs from the actual spec_name (from state_getRuntimeVersion), the merkleizeMetadata function throws an error:

Error: Spec name not expected. Received <display_name> expected <spec_name>

Root Cause

In packages/extension-ui/src/Popup/Signing/LedgerSign.tsx, the getMetadataProof function passes chain.name.toLowerCase() as the specName parameter to merkleizeMetadata:

const merkleizedMetadata = merkleizeMetadata(m, {
  base58Prefix: chain.ss58Format,
  decimals: chain.tokenDecimals,
  specName: chain.name.toLowerCase(),  // <-- Problem: this is display name, not spec_name
  specVersion: chain.specVersion,
  tokenSymbol: chain.tokenSymbol
});

The chain.name value comes from the MetadataDef.chain field, which is populated from the system_chain RPC call. This returns the human-readable display name (e.g., "Bifrost Mainnet"), not the actual runtime spec_name (e.g., "thebifrost-mainnet").

The merkleizeMetadata function internally extracts the spec_name from the raw metadata's System.Version constant and validates it against the provided specName parameter. When they don't match, it throws an error.

Example

For Bifrost Network:

• system_chain RPC returns: "Bifrost Mainnet" (display name)
• state_getRuntimeVersion RPC returns: { specName: "thebifrost-mainnet", ... }
• chain.name.toLowerCase() produces: "bifrost mainnet"
• Expected by metadata: "thebifrost-mainnet"

Result: Error: Spec name not expected. Received bifrost mainnet expected thebifrost-mainnet

Proposed Solution

Option 1: Don't pass specName (let merkleizeMetadata extract it)

The merkleizeMetadata function can extract spec_name directly from the raw metadata if the specName parameter is not provided. The validation is skipped when specName is null or undefined.

const merkleizedMetadata = merkleizeMetadata(m, {
  base58Prefix: chain.ss58Format,
  decimals: chain.tokenDecimals,
  // specName omitted - extracted from rawMetadata automatically
  specVersion: chain.specVersion,
  tokenSymbol: chain.tokenSymbol
});

Option 2: Extract spec_name from metadata explicitly

Use @polkadot/types to parse the metadata and extract the actual spec_name:

import { Metadata, TypeRegistry } from '@polkadot/types';

function getSpecNameFromMetadata(rawMetadata: Uint8Array): string {
  const registry = new TypeRegistry();
  const metadata = new Metadata(registry, rawMetadata);
  registry.setMetadata(metadata);

  const version = metadata.asLatest.pallets
    .find(p => p.name.toString() === 'System')
    ?.constants
    .find(c => c.name.toString() === 'Version');

  if (version) {
    const versionType = registry.createType(
      registry.createLookupType(version.type),
      version.value
    );
    return (versionType as any).specName.toString();
  }

  throw new Error('Could not find spec_name in metadata');
}

Option 3: Store spec_name in MetadataDef

Add specName field to MetadataDef interface and populate it from state_getRuntimeVersion RPC when fetching metadata.

Affected Chains

Any chain where system_chain display name differs from spec_name:

• Bifrost Network (mainnet, testnet, dev)
• Potentially other chains with similar naming conventions

Environment

• polkadot-js extension version: 0.62.6
• @polkadot-api/merkleize-metadata: (bundled)
• Ledger app: Generic App

Steps to Reproduce

1. Add a Ledger account for a chain where display name differs from spec_name (e.g., Bifrost Network)
2. Set Ledger app mode to "Generic" in extension settings
3. Attempt to sign any transaction
4. Observe the error: "Spec name not expected..."

Related

• @polkadot-api/merkleize-metadata validation logic
• MetadataDef interface in @polkadot/extension-inject