ocsp: Expose ResponderID in parsed Response.

ResponderID is unmarshalled into either ResponderName or
ResponderKeyHash depending on which one is present.

Fixes golang/go#14971.

Change-Id: I5ba602753d81835da531321e94898408395068dd
Reviewed-on: https://go-review.googlesource.com/34380
Reviewed-by: Adam Langley <agl@golang.org>

ocsp/ocsp.go

@@ -116,12 +116,11 @@ type basicResponse struct {
 }
 
 type responseData struct {
-	Raw              asn1.RawContent
-	Version          int           `asn1:"optional,default:0,explicit,tag:0"`
-	RawResponderName asn1.RawValue `asn1:"optional,explicit,tag:1"`
-	KeyHash          []byte        `asn1:"optional,explicit,tag:2"`
-	ProducedAt       time.Time     `asn1:"generalized"`
-	Responses        []singleResponse
+	Raw            asn1.RawContent
+	Version        int `asn1:"optional,default:0,explicit,tag:0"`
+	RawResponderID asn1.RawValue
+	ProducedAt     time.Time `asn1:"generalized"`
+	Responses      []singleResponse
 }
 
 type singleResponse struct {
@@ -363,6 +362,15 @@ type Response struct {
 	// If zero, the default is crypto.SHA1.
 	IssuerHash crypto.Hash
 
+	// RawResponderName optionally contains the DER-encoded subject of the
+	// responder certificate. Exactly one of RawResponderName and
+	// ResponderKeyHash is set.
+	RawResponderName []byte
+	// ResponderKeyHash optionally contains the SHA-1 hash of the
+	// responder's public key. Exactly one of RawResponderName and
+	// ResponderKeyHash is set.
+	ResponderKeyHash []byte
+
 	// Extensions contains raw X.509 extensions from the singleExtensions field
 	// of the OCSP response. When parsing certificates, this can be used to
 	// extract non-critical extensions that are not parsed by this package. When
@@ -494,6 +502,25 @@ func ParseResponseForCert(bytes []byte, cert, issuer *x509.Certificate) (*Respon
 		SignatureAlgorithm: getSignatureAlgorithmFromOID(basicResp.SignatureAlgorithm.Algorithm),
 	}
 
+	// Handle the ResponderID CHOICE tag. ResponderID can be flattened into
+	// TBSResponseData once https://go-review.googlesource.com/34503 has been
+	// released.
+	rawResponderID := basicResp.TBSResponseData.RawResponderID
+	switch rawResponderID.Tag {
+	case 1: // Name
+		var rdn pkix.RDNSequence
+		if rest, err := asn1.Unmarshal(rawResponderID.Bytes, &rdn); err != nil || len(rest) != 0 {
+			return nil, ParseError("invalid responder name")
+		}
+		ret.RawResponderName = rawResponderID.Bytes
+	case 2: // KeyHash
+		if rest, err := asn1.Unmarshal(rawResponderID.Bytes, &ret.ResponderKeyHash); err != nil || len(rest) != 0 {
+			return nil, ParseError("invalid responder key hash")
+		}
+	default:
+		return nil, ParseError("invalid responder id tag")
+	}
+
 	if len(basicResp.Certificates) > 0 {
 		ret.Certificate, err = x509.ParseCertificate(basicResp.Certificates[0].FullBytes)
 		if err != nil {
@@ -501,17 +528,17 @@ func ParseResponseForCert(bytes []byte, cert, issuer *x509.Certificate) (*Respon
 		}
 
 		if err := ret.CheckSignatureFrom(ret.Certificate); err != nil {
-			return nil, ParseError("bad OCSP signature")
+			return nil, ParseError("bad signature on embedded certificate: " + err.Error())
 		}
 
 		if issuer != nil {
 			if err := issuer.CheckSignature(ret.Certificate.SignatureAlgorithm, ret.Certificate.RawTBSCertificate, ret.Certificate.Signature); err != nil {
-				return nil, ParseError("bad signature on embedded certificate")
+				return nil, ParseError("bad OCSP signature: " + err.Error())
 			}
 		}
 	} else if issuer != nil {
 		if err := ret.CheckSignatureFrom(issuer); err != nil {
-			return nil, ParseError("bad OCSP signature")
+			return nil, ParseError("bad OCSP signature: " + err.Error())
 		}
 	}
 
@@ -620,8 +647,8 @@ func CreateRequest(cert, issuer *x509.Certificate, opts *RequestOptions) ([]byte
 // CreateResponse returns a DER-encoded OCSP response with the specified contents.
 // The fields in the response are populated as follows:
 //
-// The responder cert is used to populate the ResponderName field, and the certificate
-// itself is provided alongside the OCSP response signature.
+// The responder cert is used to populate the responder's name field, and the
+// certificate itself is provided alongside the OCSP response signature.
 //
 // The issuer cert is used to puplate the IssuerNameHash and IssuerKeyHash fields.
 //
@@ -649,7 +676,7 @@ func CreateResponse(issuer, responderCert *x509.Certificate, template Response,
 	}
 
 	if !template.IssuerHash.Available() {
-		return nil, fmt.Errorf("issuer hash algorithm %v not linked into binarya", template.IssuerHash)
+		return nil, fmt.Errorf("issuer hash algorithm %v not linked into binary", template.IssuerHash)
 	}
 	h := template.IssuerHash.New()
 	h.Write(publicKeyInfo.PublicKey.RightAlign())
@@ -686,17 +713,17 @@ func CreateResponse(issuer, responderCert *x509.Certificate, template Response,
 		}
 	}
 
-	responderName := asn1.RawValue{
+	rawResponderID := asn1.RawValue{
 		Class:      2, // context-specific
-		Tag:        1, // explicit tag
+		Tag:        1, // Name (explicit tag)
 		IsCompound: true,
 		Bytes:      responderCert.RawSubject,
 	}
 	tbsResponseData := responseData{
-		Version:          0,
-		RawResponderName: responderName,
-		ProducedAt:       time.Now().Truncate(time.Minute).UTC(),
-		Responses:        []singleResponse{innerResponse},
+		Version:        0,
+		RawResponderID: rawResponderID,
+		ProducedAt:     time.Now().Truncate(time.Minute).UTC(),
+		Responses:      []singleResponse{innerResponse},
 	}
 
 	tbsResponseDataDER, err := asn1.Marshal(tbsResponseData)

ocsp/ocsp_test.go

@@ -24,7 +24,13 @@ func TestOCSPDecode(t *testing.T) {
 	responseBytes, _ := hex.DecodeString(ocspResponseHex)
 	resp, err := ParseResponse(responseBytes, nil)
 	if err != nil {
-		t.Error(err)
+		t.Fatal(err)
+	}
+
+	responderCert, _ := hex.DecodeString(startComResponderCertHex)
+	responder, err := x509.ParseCertificate(responderCert)
+	if err != nil {
+		t.Fatal(err)
 	}
 
 	expected := Response{
@@ -33,6 +39,7 @@ func TestOCSPDecode(t *testing.T) {
 		RevocationReason: Unspecified,
 		ThisUpdate:       time.Date(2010, 7, 7, 15, 1, 5, 0, time.UTC),
 		NextUpdate:       time.Date(2010, 7, 7, 18, 35, 17, 0, time.UTC),
+		RawResponderName: responder.RawSubject,
 	}
 
 	if !reflect.DeepEqual(resp.ThisUpdate, expected.ThisUpdate) {
@@ -54,6 +61,14 @@ func TestOCSPDecode(t *testing.T) {
 	if resp.RevocationReason != expected.RevocationReason {
 		t.Errorf("resp.RevocationReason: got %d, want %d", resp.RevocationReason, expected.RevocationReason)
 	}
+
+	if !bytes.Equal(resp.RawResponderName, expected.RawResponderName) {
+		t.Errorf("resp.RawResponderName: got %x, want %x", resp.RawResponderName, expected.RawResponderName)
+	}
+
+	if !bytes.Equal(resp.ResponderKeyHash, expected.ResponderKeyHash) {
+		t.Errorf("resp.ResponderKeyHash: got %x, want %x", resp.ResponderKeyHash, expected.ResponderKeyHash)
+	}
 }
 
 func TestOCSPDecodeWithoutCert(t *testing.T) {
@@ -386,6 +401,41 @@ const ocspResponseHex = "308206bc0a0100a08206b5308206b106092b0601050507300101048
 	"a1d24ce16e41a9941568fec5b42771e118f16c106a54ccc339a4b02166445a167902e75e" +
 	"6d8620b0825dcd18a069b90fd851d10fa8effd409deec02860d26d8d833f304b10669b42"
 
+const startComResponderCertHex = "308204b23082039aa003020102020101300d06092a864886f70d010105050030818c310b" +
+	"300906035504061302494c31163014060355040a130d5374617274436f6d204c74642e31" +
+	"2b3029060355040b1322536563757265204469676974616c204365727469666963617465" +
+	"205369676e696e67313830360603550403132f5374617274436f6d20436c617373203120" +
+	"5072696d61727920496e7465726d65646961746520536572766572204341301e170d3037" +
+	"313032353030323330365a170d3132313032333030323330365a304c310b300906035504" +
+	"061302494c31163014060355040a130d5374617274436f6d204c74642e31253023060355" +
+	"0403131c5374617274436f6d20436c6173732031204f435350205369676e657230820122" +
+	"300d06092a864886f70d01010105000382010f003082010a0282010100b9561b4c453187" +
+	"17178084e96e178df2255e18ed8d8ecc7c2b7b51a6c1c2e6bf0aa3603066f132fe10ae97" +
+	"b50e99fa24b83fc53dd2777496387d14e1c3a9b6a4933e2ac12413d085570a95b8147414" +
+	"a0bc007c7bcf222446ef7f1a156d7ea1c577fc5f0facdfd42eb0f5974990cb2f5cefebce" +
+	"ef4d1bdc7ae5c1075c5a99a93171f2b0845b4ff0864e973fcfe32f9d7511ff87a3e94341" +
+	"0c90a4493a306b6944359340a9ca96f02b66ce67f028df2980a6aaee8d5d5d452b8b0eb9" +
+	"3f923cc1e23fcccbdbe7ffcb114d08fa7a6a3c404f825d1a0e715935cf623a8c7b596700" +
+	"14ed0622f6089a9447a7a19010f7fe58f84129a2765ea367824d1c3bb2fda30853020301" +
+	"0001a382015c30820158300c0603551d130101ff04023000300b0603551d0f0404030203" +
+	"a8301e0603551d250417301506082b0601050507030906092b0601050507300105301d06" +
+	"03551d0e0416041445e0a36695414c5dd449bc00e33cdcdbd2343e173081a80603551d23" +
+	"0481a030819d8014eb4234d098b0ab9ff41b6b08f7cc642eef0e2c45a18181a47f307d31" +
+	"0b300906035504061302494c31163014060355040a130d5374617274436f6d204c74642e" +
+	"312b3029060355040b1322536563757265204469676974616c2043657274696669636174" +
+	"65205369676e696e6731293027060355040313205374617274436f6d2043657274696669" +
+	"636174696f6e20417574686f7269747982010a30230603551d12041c301a861868747470" +
+	"3a2f2f7777772e737461727473736c2e636f6d2f302c06096086480186f842010d041f16" +
+	"1d5374617274436f6d205265766f636174696f6e20417574686f72697479300d06092a86" +
+	"4886f70d01010505000382010100182d22158f0fc0291324fa8574c49bb8ff2835085adc" +
+	"bf7b7fc4191c397ab6951328253fffe1e5ec2a7da0d50fca1a404e6968481366939e666c" +
+	"0a6209073eca57973e2fefa9ed1718e8176f1d85527ff522c08db702e3b2b180f1cbff05" +
+	"d98128252cf0f450f7dd2772f4188047f19dc85317366f94bc52d60f453a550af58e308a" +
+	"aab00ced33040b62bf37f5b1ab2a4f7f0f80f763bf4d707bc8841d7ad9385ee2a4244469" +
+	"260b6f2bf085977af9074796048ecc2f9d48a1d24ce16e41a9941568fec5b42771e118f1" +
+	"6c106a54ccc339a4b02166445a167902e75e6d8620b0825dcd18a069b90fd851d10fa8ef" +
+	"fd409deec02860d26d8d833f304b10669b42"
+
 const startComHex = "308206343082041ca003020102020118300d06092a864886f70d0101050500307d310b30" +
 	"0906035504061302494c31163014060355040a130d5374617274436f6d204c74642e312b" +
 	"3029060355040b1322536563757265204469676974616c20436572746966696361746520" +