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ASAR Integrity

ASAR integrity is an experimental feature that validates the contents of your app's ASAR archives at runtime.

Version support​

Currently, ASAR integrity checking is supported on:

  • macOS as of electron>=16.0.0
  • Windows as of electron>=30.0.0

In order to enable ASAR integrity checking, you also need to ensure that your app.asar file was generated by a version of the @electron/asar npm package that supports ASAR integrity.

Support was introduced in asar@3.1.0. Note that this package has since migrated over to @electron/asar. All versions of @electron/asar support ASAR integrity.

How it works​

Each ASAR archive contains a JSON string header. The header format includes an integrity object that contain a hex encoded hash of the entire archive as well as an array of hex encoded hashes for each block of blockSize bytes.

{
  "algorithm": "SHA256",
  "hash": "...",
  "blockSize": 1024,
  "blocks": ["...", "..."]
}

Separately, you need to define a hex encoded hash of the entire ASAR header when packaging your Electron app.

When ASAR integrity is enabled, your Electron app will verify the header hash of the ASAR archive on runtime. If no hash is present or if there is a mismatch in the hashes, the app will forcefully terminate.

Enabling ASAR integrity in the binary​

ASAR integrity checking is currently disabled by default in Electron and can be enabled on build time by toggling the EnableEmbeddedAsarIntegrityValidation Electron fuse.

When enabling this fuse, you typically also want to enable the onlyLoadAppFromAsar fuse. Otherwise, the validity checking can be bypassed via the Electron app code search path.

const { flipFuses, FuseVersion, FuseV1Options } = require('@electron/fuses')

flipFuses(
  // E.g. /a/b/Foo.app
  pathToPackagedApp,
  {
    version: FuseVersion.V1,
    [FuseV1Options.EnableEmbeddedAsarIntegrityValidation]: true,
    [FuseV1Options.OnlyLoadAppFromAsar]: true
  }
)
Fuses in Electron Forge

With Electron Forge, you can configure your app's fuses with @electron-forge/plugin-fuses in your Forge configuration file.

Providing the header hash​

ASAR integrity validates the contents of the ASAR archive against the header hash that you provide on package time. The process of providing this packaged hash is different for macOS and Windows.

Using Electron tooling​

Electron Forge and Electron Packager do this setup automatically for you with no additional configuration. The minimum required versions for ASAR integrity are:

  • @electron/packager@18.3.1
  • @electron/forge@7.4.0

Using other build systems​

macOS​

When packaging for macOS, you must populate a valid ElectronAsarIntegrity dictionary block in your packaged app's Info.plist. An example is included below.

Info.plist
<key>ElectronAsarIntegrity</key>
<dict>
  <key>Resources/app.asar</key>
  <dict>
    <key>algorithm</key>
    <string>SHA256</string>
    <key>hash</key>
    <string>9d1f61ea03c4bb62b4416387a521101b81151da0cfbe18c9f8c8b818c5cebfac</string>
  </dict>
</dict>

Valid algorithm values are currently SHA256 only. The hash is a hash of the ASAR header using the given algorithm. The @electron/asar package exposes a getRawHeader method whose result can then be hashed to generate this value (e.g. using the node:crypto module).

Windows​

When packaging for Windows, you must populate a valid resource entry of type Integrity and name ElectronAsar. The value of this resource should be a JSON encoded dictionary in the form included below:

[
  {
    "file": "resources\\app.asar",
    "alg": "sha256",
    "value": "9d1f61ea03c4bb62b4416387a521101b81151da0cfbe18c9f8c8b818c5cebfac"
  }
]
info

For an implementation example, see src/resedit.ts in the Electron Packager code.