Smart Card Support

This project has some support for integrating with Smart Cards. This enables you to perform cryptographic signing using a certificate that is stored in a hardware device.

Certificates stored this way are more secure, as it typically requires that a physical device be unlocked in order to use the private key. And access to the raw private key matter is typically not allowed.

Cargo Feature

Smart card integration requires the optional and disabled-by-default smartcard Cargo feature to be enabled.

On macOS and Windows, this feature should just work.

On Linux, you’ll need a package providing pcsclite installed or you may get a cryptic build error due to missing dependencies. On Debian based distros, you want to apt install libpcsclite1 libpcsclite-dev (or something of that nature).

Limitations

We currently use yubikey.rs for smart card integration. This likely means that only YubiKeys currently work.

However, we would like to switch to a more generic interface (such as pcsc in the future to allow more flexible usage.

There is currently no support for setting the management key. If you have set a custom management key, you won’t be able to import certificates onto your smart card. However, signing should still work.

Validating Smart Card Integration

To see if your smart card device is recognized and certificates can be found:

$ rcodesign smartcard-scan
Device 0: Yubico YubiKey OTP+FIDO+CCID 0
Device 0: Serial: 12345678
Device 0: Version: 5.2.7
Device 0: Certificate in slot Signature / 9c
Subject CN:                  gps
Issuer CN:                   gps
Subject is Issuer?:          true
Team ID:                     <missing>
SHA-1 fingerprint:           c847e830c01845517d7e3775805ab56313aa11c8
SHA-256 fingerprint:         7c0bc8fe1a2d7831ca0b0787dc6d5c28c6f562c2723a7eaaab42d39e7a3b7924
Signed by Apple?:            false
Guessed Certificate Profile: none
Is Apple Root CA?:           false
Is Apple Intermediate CA?:   false
Apple CA Extension:          none
Apple Extended Key Usage Purpose Extensions:
Apple Code Signing Extensions:

Pointing Commands at a Smart Card Certificate

rcodesign command that operate against certificates expose a --smartcard-slot argument to specify which smartcard slot to use.

Slot 9c is the standard slot for holding certificates used for signing.

To sign with your smart card certificate at slot 9c, do something like:

rcodesign sign \
    --smartcard-slot 9c \
    path/to/entity/to/sign

Smartcards often require a PIN on signing operations. You should be prompted for your PIN value if the signing operation is initially unauthenticated.

Importing Certificates Into a Smart Card

The rcodesign smartcard-import command can be used to import an existing code signing certificate into your smart card.

Let’s assume you created an Apple code signing certificate and exported it to the file developer_id.p12. You can import this certificate by doing the following:

$ rcodesign smartcard-import \
    --smartcard-slot 9c \
    --p12-file developer_id.p12 --p12-password password

$ rcodesign smartcard-scan
Device 0: Yubico YubiKey OTP+FIDO+CCID 0
Device 0: Serial: 1234567
Device 0: Version: 5.2.7
Device 0: Certificate in slot Signature / 9c
Subject CN:                  Developer ID Application: Gregory Szorc (MK22MZP987)
Issuer CN:                   Developer ID Certification Authority
Subject is Issuer?:          false
Team ID:                     MK22MZP987
SHA-1 fingerprint:           44d7155bcabf3b9a9221b01b8e198040ae04e0ad
SHA-256 fingerprint:         8f610de4caea4bc138e85b56726ed4d330f7464d99cfa5957568904b6a6375ec
Signed by Apple?:            true
Apple Issuing Chain:
  - Developer ID Certification Authority
  - Apple Root CA
  - Apple Root Certificate Authority
Guessed Certificate Profile: DeveloperIdApplication
Is Apple Root CA?:           false
Is Apple Intermediate CA?:   false
Apple CA Extension:          none
Apple Extended Key Usage Purpose Extensions:
  - 1.3.6.1.5.5.7.3.3 (CodeSigning)
Apple Code Signing Extensions:
  - 1.2.840.113635.100.6.1.33 (DeveloperIdDate)
  - 1.2.840.113635.100.6.1.13 (DeveloperIdApplication)

Creating a Certificate with a Private Key Exclusive to the Smart Card

It is possible to generate a private key directly on the smart card and create a code signing certificate derived from this private key.

Code signing certificates created this way are theoretically much more secure than other private key generation methods because most smart cards never allow the private key content to be exported/viewed. Assuming operations involving the private key are protected with the appropriate access protections (like pin or touch policies), compromise of the machine or even the smart key itself may not result in unwanted access to the private key.

To create a code signing certificate whose private key has never left the smart card device itself, do something like the following.

First, generate a new private key on the smart card:

rcodesign smartcard-generate-key --smartcard-slot 9c

Then create a certificate signing request (CSR):

rcodesign generate-certificate-signing-request \
    --smartcard-slot 9c \
    --csr-pem-path csr.pem

Then follow the instructions at Exchanging a CSR for a Code Signing Certificate to submit the CSR file to Apple and obtain a public certificate.

Finally, import the Apple-issued public certificate into the smart card:

rcodesign smartcard-import \
    --der-source developerID_application.cer \
    --smartcard-slot 9c

At this point, the smart card is ready to sign using an Apple issued certificate and the private key never has - and probably never will - leave the smart card itself.