crypto/x509: populate Number and AKI of parsed CRLs

The x509.RevocationList type has two fields which correspond to
extensions, rather than native fields, of the underlying ASN.1 CRL:
the .Number field corresponds to the crlNumber extension, and
the .AuthorityKeyId field corresponds to the authorityKeyIdentifier
extension.

The x509.CreateRevocationList() function uses these fields to populate
their respective extensions in the resulting CRL. However, the
x509.ParseRevocationList() function does not perform the reverse
operation: the fields retain their zero-values even after parsing a CRL
which contains the relevant extensions.

Add code which populates these fields when parsing their extensions.
Add assertions to the existing tests to confirm that the values are
populated appropriately.

Fixes #53726

Change-Id: Ie5b71081e53034e0b5b9ff3c122065c62f15cf23
Reviewed-on: https://go-review.googlesource.com/c/go/+/416354
Run-TryBot: Roland Shoemaker <roland@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

src/crypto/x509/parser.go

@@ -1008,22 +1008,22 @@ func ParseRevocationList(der []byte) (*RevocationList, error) {
 	// we can populate RevocationList.Raw, before unwrapping the
 	// SEQUENCE so it can be operated on
 	if !input.ReadASN1Element(&input, cryptobyte_asn1.SEQUENCE) {
-		return nil, errors.New("x509: malformed certificate")
+		return nil, errors.New("x509: malformed crl")
 	}
 	rl.Raw = input
 	if !input.ReadASN1(&input, cryptobyte_asn1.SEQUENCE) {
-		return nil, errors.New("x509: malformed certificate")
+		return nil, errors.New("x509: malformed crl")
 	}
 
 	var tbs cryptobyte.String
 	// do the same trick again as above to extract the raw
 	// bytes for Certificate.RawTBSCertificate
 	if !input.ReadASN1Element(&tbs, cryptobyte_asn1.SEQUENCE) {
-		return nil, errors.New("x509: malformed tbs certificate")
+		return nil, errors.New("x509: malformed tbs crl")
 	}
 	rl.RawTBSRevocationList = tbs
 	if !tbs.ReadASN1(&tbs, cryptobyte_asn1.SEQUENCE) {
-		return nil, errors.New("x509: malformed tbs certificate")
+		return nil, errors.New("x509: malformed tbs crl")
 	}
 
 	var version int
@@ -1148,6 +1148,15 @@ func ParseRevocationList(der []byte) (*RevocationList, error) {
 			if err != nil {
 				return nil, err
 			}
+			if ext.Id.Equal(oidExtensionAuthorityKeyId) {
+				rl.AuthorityKeyId = ext.Value
+			} else if ext.Id.Equal(oidExtensionCRLNumber) {
+				value := cryptobyte.String(ext.Value)
+				rl.Number = new(big.Int)
+				if !value.ReadASN1Integer(rl.Number) {
+					return nil, errors.New("x509: malformed crl number")
+				}
+			}
 			rl.Extensions = append(rl.Extensions, ext)
 		}
 	}

src/crypto/x509/x509.go

@@ -2109,7 +2109,9 @@ type RevocationList struct {
 	// Issuer contains the DN of the issuing certificate.
 	Issuer pkix.Name
 	// AuthorityKeyId is used to identify the public key associated with the
-	// issuing certificate.
+	// issuing certificate. It is populated from the authorityKeyIdentifier
+	// extension when parsing a CRL. It is ignored when creating a CRL; the
+	// extension is populated from the issuing certificate itself.
 	AuthorityKeyId []byte
 
 	Signature []byte
@@ -2125,7 +2127,8 @@ type RevocationList struct {
 
 	// Number is used to populate the X.509 v2 cRLNumber extension in the CRL,
 	// which should be a monotonically increasing sequence number for a given
-	// CRL scope and CRL issuer.
+	// CRL scope and CRL issuer. It is also populated from the cRLNumber
+	// extension when parsing a CRL.
 	Number *big.Int
 
 	// ThisUpdate is used to populate the thisUpdate field in the CRL, which

src/crypto/x509/x509_test.go

@@ -2681,6 +2681,19 @@ func TestCreateRevocationList(t *testing.T) {
 				t.Fatalf("Extensions mismatch: got %v; want %v.",
 					parsedCRL.Extensions[2:], tc.template.ExtraExtensions)
 			}
+
+			if tc.template.Number != nil && parsedCRL.Number == nil {
+				t.Fatalf("Generated CRL missing Number: got nil, want %s",
+					tc.template.Number.String())
+			}
+			if tc.template.Number != nil && tc.template.Number.Cmp(parsedCRL.Number) != 0 {
+				t.Fatalf("Generated CRL has wrong Number: got %s, want %s",
+					parsedCRL.Number.String(), tc.template.Number.String())
+			}
+			if !bytes.Equal(parsedCRL.AuthorityKeyId, expectedAKI) {
+				t.Fatalf("Generated CRL has wrong Number: got %x, want %x",
+					parsedCRL.AuthorityKeyId, expectedAKI)
+			}
 		})
 	}
 }