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Better error message for missing intermediates #182

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Better error message for missing intermediates #182

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40 changes: 40 additions & 0 deletions lib/verify.go
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,8 @@ import (
"encoding/pem"
"fmt"
"io"
"io/ioutil"
"net/http"
"os"
"time"

Expand Down Expand Up @@ -109,6 +111,30 @@ func caBundle(caPath string) *x509.CertPool {
return bundle
}

func fetchAIA(cert *x509.Certificate) *x509.Certificate {
for _, url := range cert.IssuingCertificateURL {
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rfc4325 says we should look at the file extension to see if it's .cer or .p7c. We could return if it's .p7c and only support .cer fetching

resp, err := http.Get(url)
if err != nil {
continue
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Should we log errors?

}

defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
continue
}

intermediate, err := x509.ParseCertificate(body)
if err != nil {
continue
}

return intermediate
}

return nil
}

func VerifyChain(certs []*x509.Certificate, ocspStaple []byte, dnsName, caPath string) SimpleVerification {
result := SimpleVerification{
Chains: [][]simpleVerifyCert{},
Expand All @@ -129,6 +155,20 @@ func VerifyChain(certs []*x509.Certificate, ocspStaple []byte, dnsName, caPath s
chains, err := certs[0].Verify(opts)
if err != nil {
result.Error = fmt.Sprintf("%s", err)

if len(intermediates.Subjects()) == 0 {
// No intermediates found, maybe broken chain. Let's try AIA fetching?
intermediate := fetchAIA(certs[0])
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We're only trying the first one in the chain? I guess it's pretty rare to have more than 3 certs in a chain.

if intermediate != nil {
intermediates.AddCert(intermediate)
_, err := certs[0].Verify(opts)
if err == nil {
// Would work with proper intermediates.
result.Error = "server is not sending required intermediate certificate(s)"
}
}
}

return result
}

Expand Down