crypto/x509: support Inhibit Any-policy and Policy Constraints

[satsrini]

Important

The current proposal is #68484 (comment).

Go version

go version go1.20.4 windows/amd64

Output of go env in your module/workspace:

GO111MODULE=
 GOARCH=amd64
 GOBIN=
 GOCACHE=C:\Users\ ****\AppData\Local\go-build
 GOENV=C:\Users\ ****\AppData\Roaming\go\env
 GOEXE=.exe
 GOEXPERIMENT=
 GOFLAGS=
 GOHOSTARCH=amd64
 GOHOSTOS=windows
 GOINSECURE=
 GOMODCACHE=C:\git\pkg\mod
 GONOPROXY=
 GONOSUMDB=
 GOOS=windows
 GOPATH=C:\git
 GOPRIVATE=
 GOPROXY=https://proxy.golang.org,direct
 GOROOT=C:\Program Files\Go
 GOSUMDB=sum.golang.org
 GOTMPDIR=
 GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
 GOVCS=
 GOVERSION=go1.20.4
 GCCGO=gccgo
 GOAMD64=v1
 AR=ar
 CC=gcc
 CXX=g++
 CGO_ENABLED=1
 GOMOD=c:\git\****\****\go.mod
 GOWORK=
 CGO_CFLAGS=-O2 -g
 CGO_CPPFLAGS=
 CGO_CXXFLAGS=-O2 -g
 CGO_FFLAGS=-O2 -g
 CGO_LDFLAGS=-O2 -g
 PKG_CONFIG=pkg-config
 GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=C:\Users\S****\AppData\Local\Temp\go-build1520036143=/tmp/go-build -gno-record-gcc-switches

What did you do?

To validate/verify the X509 certificates that contain the following X509 critical extensions using https://github.com/golang/go/blob/master/src/crypto/x509/verify.go#L753

               _a. X509v3 Policy Constraints: critical
                Require Explicit Policy:0, Inhibit Policy Mapping:0

               b. X509v3 Inhibit Any Policy: critical
                0_          

code snippet:

_,err = x509cert.Verify(x509.VerifyOptions{
		KeyUsages:     []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
		Roots:         rootCertsPool,
		Intermediates: intermediatesCertPool,
	})

What did you see happen?

It throws the error saying
"x509: unhandled critical extension"

What did you expect to see?

Certificate Verification done successfully with out any error.

Additional info:

This is because of the following code.
https://github.com/golang/go/blob/master/src/crypto/x509/parser.go#L780
https://github.com/golang/go/blob/master/src/crypto/x509/verify.go#L565

as the following Extensions OIDs are not handled in the above mentioned GO Lang code.
2.5.29.54 (Require Explicit Policy:0, Inhibit Policy Mapping:0)
2.5.29.36 (X509v3 Inhibit Any Policy: critical)

[gabyhelp]

Related Issues and Documentation

• crypto/x509: invalid certificate policies #65990 (closed)
• crypto/x509: support OIDs for tcg-kp (2.23.133.8) #47620
• crypto/x509: parse SAN DirectoryName #47618 (closed)
• crypto/x509: parseCertificate fails if Cert Policy extension is critical #9964 (closed)
• crypto/x509: error parsing large ASN.1 identifiers #49678 (closed)
• crypto/x509: Certificate.Verify does not consistently return UnknownAuthorityError #58777
• crypto/x509: Verify fails to find valid path when some paths have EKU constraint violations #48869 (closed)
• crypto/x509: malformed x509 certificate is accepted since 1.17 #51369
• crypto/x509: CreateRevocationList over-enforces KeyUsage check #59669
• crypto/x509: NameConstraintsWithoutSANs when checking signing certificate #24151 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

What certificates make use of these extensions?

[satsrini]

Hi @seankhliao , DOD certificates make use of these extensions.

eg.
download https://dl.dod.cyber.mil/wp-content/uploads/pki-pke/zip/unclass-dod_approved_external_pkis_trust_chains.zip
You can check in DoD_Approved_External_PKIs_Trust_Chains_v11.0_20240513/DigiCert_Federal_SSP/Trust_Chain_1/1-Symantec_SSP_Intermediate_CA-G4.cer

[seankhliao]

cc @golang/security

[rolandshoemaker]

We don't support policy constraints because they are basically unused in the webpki, and impose somewhat complicated constraints on path building. Federal PKI is notorious for using complex/obscure RFC 5280 features, for better or worse, which are generally unused in the wider webpki, so it doesn't surprise me that we fail to parse/process some of their hierarchies.

While I'm not aware of any restrictions on using them in publicly trusted certificates, without significant usage in webpki certificates I'm not convinced that we should add the necessary path building complexity to support policy constraints.

[satsrini]

ok, thanks a lot team.

[cherrymui]

Sounds like we can close this for now. If things change in the future and there is a necessity for support this, we can reopen. Thanks.

[sgmiller]

We're seeing this in other branches of the US government as well, all Go programs can't make TLS connections due to these attributes. Would like some sort of solution or workaround, most recently IRS.

[armon]

Wanted to chime in that we see this as broadly important to the Golang ecosystem at HashiCorp. Users and customers in the Federal space have more advanced uses of PKI that are standards compliant, but beyond the typical commercial use cases. Lack of support prevents those organizations from being able to build applications using Golang, and impacts vendors like us supporting them.