MacOS code signing and verification

signapple is a Python tool for creating, verifying, and inspecting signatures in Mach-O binaries.

It is currently targeted towards MacOS applications, however may be used with varying degrees of success for Mach-O binaries targeting other Apple operating systems. Support for those is planned in the future.

Installation

signapple can be installed from source using pip install -e . or with poetry using poetry install. This will add a command named signapple. Additionally, once all of the dependencies are installed, codesign.py will provide the same capabilities as the signapple command.

Dependencies

If you want to install dependencies manually, the dependencies are:

• asn1crypto - Certificate and CMS parsing
• oscrypto - Cryptographic signature creation and verification
• elfesteem - Mach-O binary manipulation.
• certvalidator - Certificate chain validation. Note that this is a specifically modified version to allow for Apple specific extensions.

Usage

signapple has three commands: verify, sign, and dump. verify will verify any existing code signatures. sign will create a new code signature. dump will print out information about existing code signatures.

Any paths can be either to the bundle directory or to the binary itself.

The full usage is as follows:

$ signapple --help
usage: signapple [-h] {verify,sign,dump,apply} ...

Signs and verifies MacOS code signatures

positional arguments:
  {verify,sign,dump,apply}
                        Commands
    verify              Verify the code signature for a binary
    sign                Create a code signature for a binary
    dump                Dump the code signature for a binary
    apply               Apply a detached signature

optional arguments:
  -h, --help            show this help message and exit

$ signapple verify --help
usage: signapple verify [-h] filename

positional arguments:
  filename    Path to the binary to verify

optional arguments:
  -h, --help  show this help message and exit

$ signapple sign --help
usage: signapple sign [-h] [--passphrase PASSPHRASE] [--force] [--file-list FILE_LIST] [--detach DETACH] [--no-verify] keypath filename

positional arguments:
  keypath               Path to the PKCS#12 archive containing the certificate and private key to sign with
  filename              Path to the binary to sign. It will be modified in place

optional arguments:
  -h, --help            show this help message and exit
  --passphrase PASSPHRASE, -p PASSPHRASE
                        The passphrase protecting the private key. If not specified, you will be prompted to enter it later
  --force, -f           Ignore existing signatures. Otherwise if an existing signature is found, no signing will occur
  --file-list FILE_LIST
                        Path to write out the list of modified files to
  --detach DETACH       Detach the signature and write it to this path
  --no-verify           Don't verify the signature after creating.

$ signapple dump --help
usage: signapple dump [-h] filename

positional arguments:
  filename    Path to the binary to dump

optional arguments:
  -h, --help  show this help message and exit

$ signapple apply --help
usage: signapple apply [-h] [--no-verify] filename sig

positional arguments:
  filename     The binary to attach the signature to
  sig          The directory containing the detached signature. The same path that was given to --detach during signing

optional arguments:
  -h, --help   show this help message and exit
  --no-verify  Don't verify the signature after attaching

Signing certificates

In order to sign, you must have a signing certificate. This is obtained from Apple. These certificates can then be exported as PKCS#12 files to be used with signapple. Please read the documentation for more information about certificates.

Detached signatures

The detached signatures that signapple creates are not the same detached signatures that Apple's codesign creates. Instead these detached signatures are intended to be attached to the original unsigned binary at a later date. The signatures will be placed into the target directory with a directory structure that mirrors the structure of the original application bundle. Any generated files (such as Contents/_CodeSignature/CodeResources) will be found there. The signatures will just be the embedded signature with saved in a file that has the same name as the original binary but with an extension of the format .<arch>sign where <arch> is the name of the machine architecture for that signed binary. In the case of universal binaries, there will multiple such signatures. Typically there will be .x86_64sign and .arm64sign files for universal binaries.

License

This project is available under the MIT License. See LICENSE for more information. Copyright(c) 2020 Andrew Chow.