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crypto/x509: consider parents by Subject if AKID has no match
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If a certificate somehow has an AKID, it should still chain successfully
to a parent without a SKID, even if the latter is invalid according to
RFC 5280, because only the Subject is authoritative.

This reverts to the behavior before golang#29233 was fixed in 7701306. Roots
with the right subject will still be shadowed by roots with the right
SKID and the wrong subject, but that's been the case for a long time, and
is left for a more complete fix in Go 1.13.

Updates golang#30079

Change-Id: If8ab0179aca86cb74caa926d1ef93fb5e416b4bb
Reviewed-on: https://go-review.googlesource.com/c/161097
Reviewed-by: Adam Langley <agl@golang.org>
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@FiloSottile @nebulabox
FiloSottile authored and nebulabox committed Feb 20, 2019
1 parent d0eef4d commit b1d3df6
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Showing 2 changed files with 123 additions and 2 deletions.
9 changes: 7 additions & 2 deletions src/crypto/x509/cert_pool.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -71,10 +71,15 @@ func (s *CertPool) findPotentialParents(cert *Certificate) []int {
if s == nil {
return nil
}

var candidates []int
if len(cert.AuthorityKeyId) > 0 {
return s.bySubjectKeyId[string(cert.AuthorityKeyId)]
candidates = s.bySubjectKeyId[string(cert.AuthorityKeyId)]
}
if len(candidates) == 0 {
candidates = s.byName[string(cert.RawIssuer)]
}
return s.byName[string(cert.RawIssuer)]
return candidates
}

func (s *CertPool) contains(cert *Certificate) bool {
Expand Down
116 changes: 116 additions & 0 deletions src/crypto/x509/verify_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -386,6 +386,19 @@ var verifyTests = []verifyTest{

errorCallback: expectHostnameError("not valid for any names"),
},
{
// A certificate with an AKID should still chain to a parent without SKID.
// See Issue 30079.
leaf: leafWithAKID,
roots: []string{rootWithoutSKID},
currentTime: 1550000000,
dnsName: "example",
systemSkip: true,

expectedChains: [][]string{
{"Acme LLC", "Acme Co"},
},
},
}

func expectHostnameError(msg string) func(*testing.T, int, error) bool {
Expand Down Expand Up @@ -1679,6 +1692,109 @@ h7olHCpY9yMRiz0=
-----END CERTIFICATE-----
`

const (
rootWithoutSKID = `
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
78:29:2a:dc:2f:12:39:7f:c9:33:93:ea:61:39:7d:70
Signature Algorithm: ecdsa-with-SHA256
Issuer: O = Acme Co
Validity
Not Before: Feb 4 22:56:34 2019 GMT
Not After : Feb 1 22:56:34 2029 GMT
Subject: O = Acme Co
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:84:a6:8c:69:53:af:87:4b:39:64:fe:04:24:e6:
d8:fc:d6:46:39:35:0e:92:dc:48:08:7e:02:5f:1e:
07:53:5c:d9:e0:56:c5:82:07:f6:a3:e2:ad:f6:ad:
be:a0:4e:03:87:39:67:0c:9c:46:91:68:6b:0e:8e:
f8:49:97:9d:5b
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Key Usage: critical
Digital Signature, Key Encipherment, Certificate Sign
X509v3 Extended Key Usage:
TLS Web Server Authentication
X509v3 Basic Constraints: critical
CA:TRUE
X509v3 Subject Alternative Name:
DNS:example
Signature Algorithm: ecdsa-with-SHA256
30:46:02:21:00:c6:81:61:61:42:8d:37:e7:d0:c3:72:43:44:
17:bd:84:ff:88:81:68:9a:99:08:ab:3c:3a:c0:1e:ea:8c:ba:
c0:02:21:00:de:c9:fa:e5:5e:c6:e2:db:23:64:43:a9:37:42:
72:92:7f:6e:89:38:ea:9e:2a:a7:fd:2f:ea:9a:ff:20:21:e7
-----BEGIN CERTIFICATE-----
MIIBbzCCARSgAwIBAgIQeCkq3C8SOX/JM5PqYTl9cDAKBggqhkjOPQQDAjASMRAw
DgYDVQQKEwdBY21lIENvMB4XDTE5MDIwNDIyNTYzNFoXDTI5MDIwMTIyNTYzNFow
EjEQMA4GA1UEChMHQWNtZSBDbzBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABISm
jGlTr4dLOWT+BCTm2PzWRjk1DpLcSAh+Al8eB1Nc2eBWxYIH9qPirfatvqBOA4c5
ZwycRpFoaw6O+EmXnVujTDBKMA4GA1UdDwEB/wQEAwICpDATBgNVHSUEDDAKBggr
BgEFBQcDATAPBgNVHRMBAf8EBTADAQH/MBIGA1UdEQQLMAmCB2V4YW1wbGUwCgYI
KoZIzj0EAwIDSQAwRgIhAMaBYWFCjTfn0MNyQ0QXvYT/iIFompkIqzw6wB7qjLrA
AiEA3sn65V7G4tsjZEOpN0Jykn9uiTjqniqn/S/qmv8gIec=
-----END CERTIFICATE-----
`
leafWithAKID = `
Certificate:
Data:
Version: 3 (0x2)
Serial Number:
f0:8a:62:f0:03:84:a2:cf:69:63:ad:71:3b:b6:5d:8c
Signature Algorithm: ecdsa-with-SHA256
Issuer: O = Acme Co
Validity
Not Before: Feb 4 23:06:52 2019 GMT
Not After : Feb 1 23:06:52 2029 GMT
Subject: O = Acme LLC
Subject Public Key Info:
Public Key Algorithm: id-ecPublicKey
Public-Key: (256 bit)
pub:
04:5a:4e:4d:fb:ff:17:f7:b6:13:e8:29:45:34:81:
39:ff:8c:9c:d9:8c:0a:9f:dd:b5:97:4c:2b:20:91:
1c:4f:6b:be:53:27:66:ec:4a:ad:08:93:6d:66:36:
0c:02:70:5d:01:ca:7f:c3:29:e9:4f:00:ba:b4:14:
ec:c5:c3:34:b3
ASN1 OID: prime256v1
NIST CURVE: P-256
X509v3 extensions:
X509v3 Key Usage: critical
Digital Signature, Key Encipherment
X509v3 Extended Key Usage:
TLS Web Server Authentication
X509v3 Basic Constraints: critical
CA:FALSE
X509v3 Authority Key Identifier:
keyid:C2:2B:5F:91:78:34:26:09:42:8D:6F:51:B2:C5:AF:4C:0B:DE:6A:42
X509v3 Subject Alternative Name:
DNS:example
Signature Algorithm: ecdsa-with-SHA256
30:44:02:20:64:e0:ba:56:89:63:ce:22:5e:4f:22:15:fd:3c:
35:64:9a:3a:6b:7b:9a:32:a0:7f:f7:69:8c:06:f0:00:58:b8:
02:20:09:e4:9f:6d:8b:9e:38:e1:b6:01:d5:ee:32:a4:94:65:
93:2a:78:94:bb:26:57:4b:c7:dd:6c:3d:40:2b:63:90
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
`
)

var unknownAuthorityErrorTests = []struct {
cert string
expected string
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