crypto/x509: Support critical Apple extension for Development and Submission signing

[nathany]

What version of Go are you using (go version)?

go version devel +eced964 Tue Apr 14 17:19:36 2015 +0000 darwin/amd64

What operating system and processor architecture are you using?

darwin/amd64

What did you do?

I am using the Azure go-pkcs12 package to load a .p12 file exported from my Mac keychain. The PEM data from this library looks good and is without error, but X509KeyPair fails with:

x509: unhandled critical extension

package main

import (
    "crypto/tls"
    "encoding/pem"
    "io/ioutil"
    "log"

    "github.com/Azure/go-pkcs12"
)

func main() {
    p12, err := ioutil.ReadFile("Certificates.p12")
    if err != nil {
        log.Fatal(err)
    }

    blocks, err := pkcs12.ConvertToPEM(p12, "password")
    if err != nil {
        log.Fatal(err)
    }

    pemData := []byte{}
    for _, b := range blocks {
        pemData = append(pemData, pem.EncodeToMemory(b)...)
    }

    log.Println(string(pemData))

    // then use PEM data for tls to construct tls certificate:

    cert, err := tls.X509KeyPair(pemData, pemData)
    if err != nil {
        log.Fatal(err)
    }

    _ = cert
}

What did you expect to see?

A valid tls.X509KeyPair without error.

I would like to be able to load .p12 files directly to use with https://github.com/timehop/apns for push notifications. Currently I need to use OpenSSL (bindings) to do the conversion to a format Go understands.

What did you see instead?

x509: unhandled critical extension

This is failing because there are "Unknown extensions cause an error if marked as critical." (src)

In this case, the failing extension is 1.2.840.113635.100.6.1.2.0.0 APPLE_EXTENSION_ADC_APPLE_SIGNING which is flagged as critical.

[minux]

We cannot skip extensions marked critical.

[nathany]

In that case, maybe there is a way I can strip out some extensions before sending it through to tls.X509KeyPair.

Or what would need to be done to support these extensions?

[bradfitz]

Where is the definition of APPLE_EXTENSION_ADC_APPLE_SIGNING?

/cc @agl

[nathany]

Googling for "1.2.840.113635.100.6.1.2.0.0" turned up this source file.

I'll see if I can find some better info.

[nathany]

Here we go: http://images.apple.com/certificateauthority/pdf/Apple_WWDR_CPS_v1.0.pdf

Update: newer version of that document http://images.apple.com/certificateauthority/pdf/Apple_WWDR_CPS_v1.12.pdf

iPhone Software Development Signing (1.2.840.113635.100.6.1.2), critical (Development
Certificates)

I'm assuming it's marked critical because it is flagging this as a development certificate.

[nathany]

In addition to critical extensions for iPhone certs:

iPhone Software Submission Signing (1.2.840.113635.100.6.1.4)
iPhone Software Development Signing (1.2.840.113635.100.6.1.2)

There are critical extensions for Safari, Mac, etc. listed in that document.

Extended Key Usage - Safari Extension Signing (1.2.840.113635.100.4.8)
Custom Extensions - Safari Extension Signing (1.2.840.113635.100.6.1.5)

But I'm not seeing information on what the values mean. My development cert contained Value:[]uint8{0x5, 0x0} but I don't know what that means. 😦

[agl]

I think a reasonable change here might be for X509KeyPair to ignore errors in the certificate. As a server, it doesn't really matter to you what's in the certificate that you send to the clients except for sanity checks and for SNI matching.

Would that be sufficient for you?

Another option would be that unknown critical extensions were no longer a parse-time error, but rather caused validation to fail.

[nathany]

Upon further investigation, I think I was using the wrong cert, as a push notification cert doesn't have critical extensions based on the docs. I need to check with a colleague that I have the right certs and double check if this is still an issue for me. [Update: Confirmed, this isn't an issue for me right now, but it would be something nice to resolve for future use.]

Also, I think the error handling could be improved. If instead of:

x509: unhandled critical extension

It could include the ID

x509: unhandled critical extension (1.2.840.113635.100.6.1.2.0.0)

It would've been a lot easier to hunt down the issue.

[gopherbot]

CL https://golang.org/cl/9390 mentions this issue.