ocsp.go

Documentation: golang.org/x/crypto/ocsp

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package ocsp parses OCSP responses as specified in RFC 2560. OCSP responses
     6  // are signed messages attesting to the validity of a certificate for a small
     7  // period of time. This is used to manage revocation for X.509 certificates.
     8  package ocsp
     9  
    10  import (
    11  	"crypto"
    12  	"crypto/ecdsa"
    13  	"crypto/elliptic"
    14  	"crypto/rand"
    15  	"crypto/rsa"
    16  	_ "crypto/sha1"
    17  	_ "crypto/sha256"
    18  	_ "crypto/sha512"
    19  	"crypto/x509"
    20  	"crypto/x509/pkix"
    21  	"encoding/asn1"
    22  	"errors"
    23  	"fmt"
    24  	"math/big"
    25  	"strconv"
    26  	"time"
    27  )
    28  
    29  var idPKIXOCSPBasic = asn1.ObjectIdentifier([]int{1, 3, 6, 1, 5, 5, 7, 48, 1, 1})
    30  
    31  // ResponseStatus contains the result of an OCSP request. See
    32  // https://tools.ietf.org/html/rfc6960#section-2.3
    33  type ResponseStatus int
    34  
    35  const (
    36  	Success       ResponseStatus = 0
    37  	Malformed     ResponseStatus = 1
    38  	InternalError ResponseStatus = 2
    39  	TryLater      ResponseStatus = 3
    40  	// Status code four is unused in OCSP. See
    41  	// https://tools.ietf.org/html/rfc6960#section-4.2.1
    42  	SignatureRequired ResponseStatus = 5
    43  	Unauthorized      ResponseStatus = 6
    44  )
    45  
    46  func (r ResponseStatus) String() string {
    47  	switch r {
    48  	case Success:
    49  		return "success"
    50  	case Malformed:
    51  		return "malformed"
    52  	case InternalError:
    53  		return "internal error"
    54  	case TryLater:
    55  		return "try later"
    56  	case SignatureRequired:
    57  		return "signature required"
    58  	case Unauthorized:
    59  		return "unauthorized"
    60  	default:
    61  		return "unknown OCSP status: " + strconv.Itoa(int(r))
    62  	}
    63  }
    64  
    65  // ResponseError is an error that may be returned by ParseResponse to indicate
    66  // that the response itself is an error, not just that it's indicating that a
    67  // certificate is revoked, unknown, etc.
    68  type ResponseError struct {
    69  	Status ResponseStatus
    70  }
    71  
    72  func (r ResponseError) Error() string {
    73  	return "ocsp: error from server: " + r.Status.String()
    74  }
    75  
    76  // These are internal structures that reflect the ASN.1 structure of an OCSP
    77  // response. See RFC 2560, section 4.2.
    78  
    79  type certID struct {
    80  	HashAlgorithm pkix.AlgorithmIdentifier
    81  	NameHash      []byte
    82  	IssuerKeyHash []byte
    83  	SerialNumber  *big.Int
    84  }
    85  
    86  // https://tools.ietf.org/html/rfc2560#section-4.1.1
    87  type ocspRequest struct {
    88  	TBSRequest tbsRequest
    89  }
    90  
    91  type tbsRequest struct {
    92  	Version       int              `asn1:"explicit,tag:0,default:0,optional"`
    93  	RequestorName pkix.RDNSequence `asn1:"explicit,tag:1,optional"`
    94  	RequestList   []request
    95  }
    96  
    97  type request struct {
    98  	Cert certID
    99  }
   100  
   101  type responseASN1 struct {
   102  	Status   asn1.Enumerated
   103  	Response responseBytes `asn1:"explicit,tag:0,optional"`
   104  }
   105  
   106  type responseBytes struct {
   107  	ResponseType asn1.ObjectIdentifier
   108  	Response     []byte
   109  }
   110  
   111  type basicResponse struct {
   112  	TBSResponseData    responseData
   113  	SignatureAlgorithm pkix.AlgorithmIdentifier
   114  	Signature          asn1.BitString
   115  	Certificates       []asn1.RawValue `asn1:"explicit,tag:0,optional"`
   116  }
   117  
   118  type responseData struct {
   119  	Raw            asn1.RawContent
   120  	Version        int `asn1:"optional,default:0,explicit,tag:0"`
   121  	RawResponderID asn1.RawValue
   122  	ProducedAt     time.Time `asn1:"generalized"`
   123  	Responses      []singleResponse
   124  }
   125  
   126  type singleResponse struct {
   127  	CertID           certID
   128  	Good             asn1.Flag        `asn1:"tag:0,optional"`
   129  	Revoked          revokedInfo      `asn1:"tag:1,optional"`
   130  	Unknown          asn1.Flag        `asn1:"tag:2,optional"`
   131  	ThisUpdate       time.Time        `asn1:"generalized"`
   132  	NextUpdate       time.Time        `asn1:"generalized,explicit,tag:0,optional"`
   133  	SingleExtensions []pkix.Extension `asn1:"explicit,tag:1,optional"`
   134  }
   135  
   136  type revokedInfo struct {
   137  	RevocationTime time.Time       `asn1:"generalized"`
   138  	Reason         asn1.Enumerated `asn1:"explicit,tag:0,optional"`
   139  }
   140  
   141  var (
   142  	oidSignatureMD2WithRSA      = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 2}
   143  	oidSignatureMD5WithRSA      = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 4}
   144  	oidSignatureSHA1WithRSA     = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 5}
   145  	oidSignatureSHA256WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 11}
   146  	oidSignatureSHA384WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 12}
   147  	oidSignatureSHA512WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 13}
   148  	oidSignatureDSAWithSHA1     = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 3}
   149  	oidSignatureDSAWithSHA256   = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 3, 2}
   150  	oidSignatureECDSAWithSHA1   = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 1}
   151  	oidSignatureECDSAWithSHA256 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 2}
   152  	oidSignatureECDSAWithSHA384 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 3}
   153  	oidSignatureECDSAWithSHA512 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 4}
   154  )
   155  
   156  var hashOIDs = map[crypto.Hash]asn1.ObjectIdentifier{
   157  	crypto.SHA1:   asn1.ObjectIdentifier([]int{1, 3, 14, 3, 2, 26}),
   158  	crypto.SHA256: asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 1}),
   159  	crypto.SHA384: asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 2}),
   160  	crypto.SHA512: asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 3}),
   161  }
   162  
   163  // TODO(rlb): This is also from crypto/x509, so same comment as AGL's below
   164  var signatureAlgorithmDetails = []struct {
   165  	algo       x509.SignatureAlgorithm
   166  	oid        asn1.ObjectIdentifier
   167  	pubKeyAlgo x509.PublicKeyAlgorithm
   168  	hash       crypto.Hash
   169  }{
   170  	{x509.MD2WithRSA, oidSignatureMD2WithRSA, x509.RSA, crypto.Hash(0) /* no value for MD2 */},
   171  	{x509.MD5WithRSA, oidSignatureMD5WithRSA, x509.RSA, crypto.MD5},
   172  	{x509.SHA1WithRSA, oidSignatureSHA1WithRSA, x509.RSA, crypto.SHA1},
   173  	{x509.SHA256WithRSA, oidSignatureSHA256WithRSA, x509.RSA, crypto.SHA256},
   174  	{x509.SHA384WithRSA, oidSignatureSHA384WithRSA, x509.RSA, crypto.SHA384},
   175  	{x509.SHA512WithRSA, oidSignatureSHA512WithRSA, x509.RSA, crypto.SHA512},
   176  	{x509.DSAWithSHA1, oidSignatureDSAWithSHA1, x509.DSA, crypto.SHA1},
   177  	{x509.DSAWithSHA256, oidSignatureDSAWithSHA256, x509.DSA, crypto.SHA256},
   178  	{x509.ECDSAWithSHA1, oidSignatureECDSAWithSHA1, x509.ECDSA, crypto.SHA1},
   179  	{x509.ECDSAWithSHA256, oidSignatureECDSAWithSHA256, x509.ECDSA, crypto.SHA256},
   180  	{x509.ECDSAWithSHA384, oidSignatureECDSAWithSHA384, x509.ECDSA, crypto.SHA384},
   181  	{x509.ECDSAWithSHA512, oidSignatureECDSAWithSHA512, x509.ECDSA, crypto.SHA512},
   182  }
   183  
   184  // TODO(rlb): This is also from crypto/x509, so same comment as AGL's below
   185  func signingParamsForPublicKey(pub interface{}, requestedSigAlgo x509.SignatureAlgorithm) (hashFunc crypto.Hash, sigAlgo pkix.AlgorithmIdentifier, err error) {
   186  	var pubType x509.PublicKeyAlgorithm
   187  
   188  	switch pub := pub.(type) {
   189  	case *rsa.PublicKey:
   190  		pubType = x509.RSA
   191  		hashFunc = crypto.SHA256
   192  		sigAlgo.Algorithm = oidSignatureSHA256WithRSA
   193  		sigAlgo.Parameters = asn1.RawValue{
   194  			Tag: 5,
   195  		}
   196  
   197  	case *ecdsa.PublicKey:
   198  		pubType = x509.ECDSA
   199  
   200  		switch pub.Curve {
   201  		case elliptic.P224(), elliptic.P256():
   202  			hashFunc = crypto.SHA256
   203  			sigAlgo.Algorithm = oidSignatureECDSAWithSHA256
   204  		case elliptic.P384():
   205  			hashFunc = crypto.SHA384
   206  			sigAlgo.Algorithm = oidSignatureECDSAWithSHA384
   207  		case elliptic.P521():
   208  			hashFunc = crypto.SHA512
   209  			sigAlgo.Algorithm = oidSignatureECDSAWithSHA512
   210  		default:
   211  			err = errors.New("x509: unknown elliptic curve")
   212  		}
   213  
   214  	default:
   215  		err = errors.New("x509: only RSA and ECDSA keys supported")
   216  	}
   217  
   218  	if err != nil {
   219  		return
   220  	}
   221  
   222  	if requestedSigAlgo == 0 {
   223  		return
   224  	}
   225  
   226  	found := false
   227  	for _, details := range signatureAlgorithmDetails {
   228  		if details.algo == requestedSigAlgo {
   229  			if details.pubKeyAlgo != pubType {
   230  				err = errors.New("x509: requested SignatureAlgorithm does not match private key type")
   231  				return
   232  			}
   233  			sigAlgo.Algorithm, hashFunc = details.oid, details.hash
   234  			if hashFunc == 0 {
   235  				err = errors.New("x509: cannot sign with hash function requested")
   236  				return
   237  			}
   238  			found = true
   239  			break
   240  		}
   241  	}
   242  
   243  	if !found {
   244  		err = errors.New("x509: unknown SignatureAlgorithm")
   245  	}
   246  
   247  	return
   248  }
   249  
   250  // TODO(agl): this is taken from crypto/x509 and so should probably be exported
   251  // from crypto/x509 or crypto/x509/pkix.
   252  func getSignatureAlgorithmFromOID(oid asn1.ObjectIdentifier) x509.SignatureAlgorithm {
   253  	for _, details := range signatureAlgorithmDetails {
   254  		if oid.Equal(details.oid) {
   255  			return details.algo
   256  		}
   257  	}
   258  	return x509.UnknownSignatureAlgorithm
   259  }
   260  
   261  // TODO(rlb): This is not taken from crypto/x509, but it's of the same general form.
   262  func getHashAlgorithmFromOID(target asn1.ObjectIdentifier) crypto.Hash {
   263  	for hash, oid := range hashOIDs {
   264  		if oid.Equal(target) {
   265  			return hash
   266  		}
   267  	}
   268  	return crypto.Hash(0)
   269  }
   270  
   271  func getOIDFromHashAlgorithm(target crypto.Hash) asn1.ObjectIdentifier {
   272  	for hash, oid := range hashOIDs {
   273  		if hash == target {
   274  			return oid
   275  		}
   276  	}
   277  	return nil
   278  }
   279  
   280  // This is the exposed reflection of the internal OCSP structures.
   281  
   282  // The status values that can be expressed in OCSP. See RFC 6960.
   283  // These are used for the Response.Status field.
   284  const (
   285  	// Good means that the certificate is valid.
   286  	Good = 0
   287  	// Revoked means that the certificate has been deliberately revoked.
   288  	Revoked = 1
   289  	// Unknown means that the OCSP responder doesn't know about the certificate.
   290  	Unknown = 2
   291  	// ServerFailed is unused and was never used (see
   292  	// https://go-review.googlesource.com/#/c/18944). ParseResponse will
   293  	// return a ResponseError when an error response is parsed.
   294  	ServerFailed = 3
   295  )
   296  
   297  // The enumerated reasons for revoking a certificate. See RFC 5280.
   298  const (
   299  	Unspecified          = 0
   300  	KeyCompromise        = 1
   301  	CACompromise         = 2
   302  	AffiliationChanged   = 3
   303  	Superseded           = 4
   304  	CessationOfOperation = 5
   305  	CertificateHold      = 6
   306  
   307  	RemoveFromCRL      = 8
   308  	PrivilegeWithdrawn = 9
   309  	AACompromise       = 10
   310  )
   311  
   312  // Request represents an OCSP request. See RFC 6960.
   313  type Request struct {
   314  	HashAlgorithm  crypto.Hash
   315  	IssuerNameHash []byte
   316  	IssuerKeyHash  []byte
   317  	SerialNumber   *big.Int
   318  }
   319  
   320  // Marshal marshals the OCSP request to ASN.1 DER encoded form.
   321  func (req *Request) Marshal() ([]byte, error) {
   322  	hashAlg := getOIDFromHashAlgorithm(req.HashAlgorithm)
   323  	if hashAlg == nil {
   324  		return nil, errors.New("Unknown hash algorithm")
   325  	}
   326  	return asn1.Marshal(ocspRequest{
   327  		tbsRequest{
   328  			Version: 0,
   329  			RequestList: []request{
   330  				{
   331  					Cert: certID{
   332  						pkix.AlgorithmIdentifier{
   333  							Algorithm:  hashAlg,
   334  							Parameters: asn1.RawValue{Tag: 5 /* ASN.1 NULL */},
   335  						},
   336  						req.IssuerNameHash,
   337  						req.IssuerKeyHash,
   338  						req.SerialNumber,
   339  					},
   340  				},
   341  			},
   342  		},
   343  	})
   344  }
   345  
   346  // Response represents an OCSP response containing a single SingleResponse. See
   347  // RFC 6960.
   348  type Response struct {
   349  	Raw []byte
   350  
   351  	// Status is one of {Good, Revoked, Unknown}
   352  	Status                                        int
   353  	SerialNumber                                  *big.Int
   354  	ProducedAt, ThisUpdate, NextUpdate, RevokedAt time.Time
   355  	RevocationReason                              int
   356  	Certificate                                   *x509.Certificate
   357  	// TBSResponseData contains the raw bytes of the signed response. If
   358  	// Certificate is nil then this can be used to verify Signature.
   359  	TBSResponseData    []byte
   360  	Signature          []byte
   361  	SignatureAlgorithm x509.SignatureAlgorithm
   362  
   363  	// IssuerHash is the hash used to compute the IssuerNameHash and IssuerKeyHash.
   364  	// Valid values are crypto.SHA1, crypto.SHA256, crypto.SHA384, and crypto.SHA512.
   365  	// If zero, the default is crypto.SHA1.
   366  	IssuerHash crypto.Hash
   367  
   368  	// RawResponderName optionally contains the DER-encoded subject of the
   369  	// responder certificate. Exactly one of RawResponderName and
   370  	// ResponderKeyHash is set.
   371  	RawResponderName []byte
   372  	// ResponderKeyHash optionally contains the SHA-1 hash of the
   373  	// responder's public key. Exactly one of RawResponderName and
   374  	// ResponderKeyHash is set.
   375  	ResponderKeyHash []byte
   376  
   377  	// Extensions contains raw X.509 extensions from the singleExtensions field
   378  	// of the OCSP response. When parsing certificates, this can be used to
   379  	// extract non-critical extensions that are not parsed by this package. When
   380  	// marshaling OCSP responses, the Extensions field is ignored, see
   381  	// ExtraExtensions.
   382  	Extensions []pkix.Extension
   383  
   384  	// ExtraExtensions contains extensions to be copied, raw, into any marshaled
   385  	// OCSP response (in the singleExtensions field). Values override any
   386  	// extensions that would otherwise be produced based on the other fields. The
   387  	// ExtraExtensions field is not populated when parsing certificates, see
   388  	// Extensions.
   389  	ExtraExtensions []pkix.Extension
   390  }
   391  
   392  // These are pre-serialized error responses for the various non-success codes
   393  // defined by OCSP. The Unauthorized code in particular can be used by an OCSP
   394  // responder that supports only pre-signed responses as a response to requests
   395  // for certificates with unknown status. See RFC 5019.
   396  var (
   397  	MalformedRequestErrorResponse = []byte{0x30, 0x03, 0x0A, 0x01, 0x01}
   398  	InternalErrorErrorResponse    = []byte{0x30, 0x03, 0x0A, 0x01, 0x02}
   399  	TryLaterErrorResponse         = []byte{0x30, 0x03, 0x0A, 0x01, 0x03}
   400  	SigRequredErrorResponse       = []byte{0x30, 0x03, 0x0A, 0x01, 0x05}
   401  	UnauthorizedErrorResponse     = []byte{0x30, 0x03, 0x0A, 0x01, 0x06}
   402  )
   403  
   404  // CheckSignatureFrom checks that the signature in resp is a valid signature
   405  // from issuer. This should only be used if resp.Certificate is nil. Otherwise,
   406  // the OCSP response contained an intermediate certificate that created the
   407  // signature. That signature is checked by ParseResponse and only
   408  // resp.Certificate remains to be validated.
   409  func (resp *Response) CheckSignatureFrom(issuer *x509.Certificate) error {
   410  	return issuer.CheckSignature(resp.SignatureAlgorithm, resp.TBSResponseData, resp.Signature)
   411  }
   412  
   413  // ParseError results from an invalid OCSP response.
   414  type ParseError string
   415  
   416  func (p ParseError) Error() string {
   417  	return string(p)
   418  }
   419  
   420  // ParseRequest parses an OCSP request in DER form. It only supports
   421  // requests for a single certificate. Signed requests are not supported.
   422  // If a request includes a signature, it will result in a ParseError.
   423  func ParseRequest(bytes []byte) (*Request, error) {
   424  	var req ocspRequest
   425  	rest, err := asn1.Unmarshal(bytes, &req)
   426  	if err != nil {
   427  		return nil, err
   428  	}
   429  	if len(rest) > 0 {
   430  		return nil, ParseError("trailing data in OCSP request")
   431  	}
   432  
   433  	if len(req.TBSRequest.RequestList) == 0 {
   434  		return nil, ParseError("OCSP request contains no request body")
   435  	}
   436  	innerRequest := req.TBSRequest.RequestList[0]
   437  
   438  	hashFunc := getHashAlgorithmFromOID(innerRequest.Cert.HashAlgorithm.Algorithm)
   439  	if hashFunc == crypto.Hash(0) {
   440  		return nil, ParseError("OCSP request uses unknown hash function")
   441  	}
   442  
   443  	return &Request{
   444  		HashAlgorithm:  hashFunc,
   445  		IssuerNameHash: innerRequest.Cert.NameHash,
   446  		IssuerKeyHash:  innerRequest.Cert.IssuerKeyHash,
   447  		SerialNumber:   innerRequest.Cert.SerialNumber,
   448  	}, nil
   449  }
   450  
   451  // ParseResponse parses an OCSP response in DER form. The response must contain
   452  // only one certificate status. To parse the status of a specific certificate
   453  // from a response which may contain multiple statuses, use ParseResponseForCert
   454  // instead.
   455  //
   456  // If the response contains an embedded certificate, then that certificate will
   457  // be used to verify the response signature. If the response contains an
   458  // embedded certificate and issuer is not nil, then issuer will be used to verify
   459  // the signature on the embedded certificate.
   460  //
   461  // If the response does not contain an embedded certificate and issuer is not
   462  // nil, then issuer will be used to verify the response signature.
   463  //
   464  // Invalid responses and parse failures will result in a ParseError.
   465  // Error responses will result in a ResponseError.
   466  func ParseResponse(bytes []byte, issuer *x509.Certificate) (*Response, error) {
   467  	return ParseResponseForCert(bytes, nil, issuer)
   468  }
   469  
   470  // ParseResponseForCert acts identically to ParseResponse, except it supports
   471  // parsing responses that contain multiple statuses. If the response contains
   472  // multiple statuses and cert is not nil, then ParseResponseForCert will return
   473  // the first status which contains a matching serial, otherwise it will return an
   474  // error. If cert is nil, then the first status in the response will be returned.
   475  func ParseResponseForCert(bytes []byte, cert, issuer *x509.Certificate) (*Response, error) {
   476  	var resp responseASN1
   477  	rest, err := asn1.Unmarshal(bytes, &resp)
   478  	if err != nil {
   479  		return nil, err
   480  	}
   481  	if len(rest) > 0 {
   482  		return nil, ParseError("trailing data in OCSP response")
   483  	}
   484  
   485  	if status := ResponseStatus(resp.Status); status != Success {
   486  		return nil, ResponseError{status}
   487  	}
   488  
   489  	if !resp.Response.ResponseType.Equal(idPKIXOCSPBasic) {
   490  		return nil, ParseError("bad OCSP response type")
   491  	}
   492  
   493  	var basicResp basicResponse
   494  	rest, err = asn1.Unmarshal(resp.Response.Response, &basicResp)
   495  	if err != nil {
   496  		return nil, err
   497  	}
   498  	if len(rest) > 0 {
   499  		return nil, ParseError("trailing data in OCSP response")
   500  	}
   501  
   502  	if n := len(basicResp.TBSResponseData.Responses); n == 0 || cert == nil && n > 1 {
   503  		return nil, ParseError("OCSP response contains bad number of responses")
   504  	}
   505  
   506  	var singleResp singleResponse
   507  	if cert == nil {
   508  		singleResp = basicResp.TBSResponseData.Responses[0]
   509  	} else {
   510  		match := false
   511  		for _, resp := range basicResp.TBSResponseData.Responses {
   512  			if cert.SerialNumber.Cmp(resp.CertID.SerialNumber) == 0 {
   513  				singleResp = resp
   514  				match = true
   515  				break
   516  			}
   517  		}
   518  		if !match {
   519  			return nil, ParseError("no response matching the supplied certificate")
   520  		}
   521  	}
   522  
   523  	ret := &Response{
   524  		Raw:                bytes,
   525  		TBSResponseData:    basicResp.TBSResponseData.Raw,
   526  		Signature:          basicResp.Signature.RightAlign(),
   527  		SignatureAlgorithm: getSignatureAlgorithmFromOID(basicResp.SignatureAlgorithm.Algorithm),
   528  		Extensions:         singleResp.SingleExtensions,
   529  		SerialNumber:       singleResp.CertID.SerialNumber,
   530  		ProducedAt:         basicResp.TBSResponseData.ProducedAt,
   531  		ThisUpdate:         singleResp.ThisUpdate,
   532  		NextUpdate:         singleResp.NextUpdate,
   533  	}
   534  
   535  	// Handle the ResponderID CHOICE tag. ResponderID can be flattened into
   536  	// TBSResponseData once https://go-review.googlesource.com/34503 has been
   537  	// released.
   538  	rawResponderID := basicResp.TBSResponseData.RawResponderID
   539  	switch rawResponderID.Tag {
   540  	case 1: // Name
   541  		var rdn pkix.RDNSequence
   542  		if rest, err := asn1.Unmarshal(rawResponderID.Bytes, &rdn); err != nil || len(rest) != 0 {
   543  			return nil, ParseError("invalid responder name")
   544  		}
   545  		ret.RawResponderName = rawResponderID.Bytes
   546  	case 2: // KeyHash
   547  		if rest, err := asn1.Unmarshal(rawResponderID.Bytes, &ret.ResponderKeyHash); err != nil || len(rest) != 0 {
   548  			return nil, ParseError("invalid responder key hash")
   549  		}
   550  	default:
   551  		return nil, ParseError("invalid responder id tag")
   552  	}
   553  
   554  	if len(basicResp.Certificates) > 0 {
   555  		// Responders should only send a single certificate (if they
   556  		// send any) that connects the responder's certificate to the
   557  		// original issuer. We accept responses with multiple
   558  		// certificates due to a number responders sending them[1], but
   559  		// ignore all but the first.
   560  		//
   561  		// [1] https://github.com/golang/go/issues/21527
   562  		ret.Certificate, err = x509.ParseCertificate(basicResp.Certificates[0].FullBytes)
   563  		if err != nil {
   564  			return nil, err
   565  		}
   566  
   567  		if err := ret.CheckSignatureFrom(ret.Certificate); err != nil {
   568  			return nil, ParseError("bad signature on embedded certificate: " + err.Error())
   569  		}
   570  
   571  		if issuer != nil {
   572  			if err := issuer.CheckSignature(ret.Certificate.SignatureAlgorithm, ret.Certificate.RawTBSCertificate, ret.Certificate.Signature); err != nil {
   573  				return nil, ParseError("bad OCSP signature: " + err.Error())
   574  			}
   575  		}
   576  	} else if issuer != nil {
   577  		if err := ret.CheckSignatureFrom(issuer); err != nil {
   578  			return nil, ParseError("bad OCSP signature: " + err.Error())
   579  		}
   580  	}
   581  
   582  	for _, ext := range singleResp.SingleExtensions {
   583  		if ext.Critical {
   584  			return nil, ParseError("unsupported critical extension")
   585  		}
   586  	}
   587  
   588  	for h, oid := range hashOIDs {
   589  		if singleResp.CertID.HashAlgorithm.Algorithm.Equal(oid) {
   590  			ret.IssuerHash = h
   591  			break
   592  		}
   593  	}
   594  	if ret.IssuerHash == 0 {
   595  		return nil, ParseError("unsupported issuer hash algorithm")
   596  	}
   597  
   598  	switch {
   599  	case bool(singleResp.Good):
   600  		ret.Status = Good
   601  	case bool(singleResp.Unknown):
   602  		ret.Status = Unknown
   603  	default:
   604  		ret.Status = Revoked
   605  		ret.RevokedAt = singleResp.Revoked.RevocationTime
   606  		ret.RevocationReason = int(singleResp.Revoked.Reason)
   607  	}
   608  
   609  	return ret, nil
   610  }
   611  
   612  // RequestOptions contains options for constructing OCSP requests.
   613  type RequestOptions struct {
   614  	// Hash contains the hash function that should be used when
   615  	// constructing the OCSP request. If zero, SHA-1 will be used.
   616  	Hash crypto.Hash
   617  }
   618  
   619  func (opts *RequestOptions) hash() crypto.Hash {
   620  	if opts == nil || opts.Hash == 0 {
   621  		// SHA-1 is nearly universally used in OCSP.
   622  		return crypto.SHA1
   623  	}
   624  	return opts.Hash
   625  }
   626  
   627  // CreateRequest returns a DER-encoded, OCSP request for the status of cert. If
   628  // opts is nil then sensible defaults are used.
   629  func CreateRequest(cert, issuer *x509.Certificate, opts *RequestOptions) ([]byte, error) {
   630  	hashFunc := opts.hash()
   631  
   632  	// OCSP seems to be the only place where these raw hash identifiers are
   633  	// used. I took the following from
   634  	// http://msdn.microsoft.com/en-us/library/ff635603.aspx
   635  	_, ok := hashOIDs[hashFunc]
   636  	if !ok {
   637  		return nil, x509.ErrUnsupportedAlgorithm
   638  	}
   639  
   640  	if !hashFunc.Available() {
   641  		return nil, x509.ErrUnsupportedAlgorithm
   642  	}
   643  	h := opts.hash().New()
   644  
   645  	var publicKeyInfo struct {
   646  		Algorithm pkix.AlgorithmIdentifier
   647  		PublicKey asn1.BitString
   648  	}
   649  	if _, err := asn1.Unmarshal(issuer.RawSubjectPublicKeyInfo, &publicKeyInfo); err != nil {
   650  		return nil, err
   651  	}
   652  
   653  	h.Write(publicKeyInfo.PublicKey.RightAlign())
   654  	issuerKeyHash := h.Sum(nil)
   655  
   656  	h.Reset()
   657  	h.Write(issuer.RawSubject)
   658  	issuerNameHash := h.Sum(nil)
   659  
   660  	req := &Request{
   661  		HashAlgorithm:  hashFunc,
   662  		IssuerNameHash: issuerNameHash,
   663  		IssuerKeyHash:  issuerKeyHash,
   664  		SerialNumber:   cert.SerialNumber,
   665  	}
   666  	return req.Marshal()
   667  }
   668  
   669  // CreateResponse returns a DER-encoded OCSP response with the specified contents.
   670  // The fields in the response are populated as follows:
   671  //
   672  // The responder cert is used to populate the responder's name field, and the
   673  // certificate itself is provided alongside the OCSP response signature.
   674  //
   675  // The issuer cert is used to populate the IssuerNameHash and IssuerKeyHash fields.
   676  //
   677  // The template is used to populate the SerialNumber, Status, RevokedAt,
   678  // RevocationReason, ThisUpdate, and NextUpdate fields.
   679  //
   680  // If template.IssuerHash is not set, SHA1 will be used.
   681  //
   682  // The ProducedAt date is automatically set to the current date, to the nearest minute.
   683  func CreateResponse(issuer, responderCert *x509.Certificate, template Response, priv crypto.Signer) ([]byte, error) {
   684  	var publicKeyInfo struct {
   685  		Algorithm pkix.AlgorithmIdentifier
   686  		PublicKey asn1.BitString
   687  	}
   688  	if _, err := asn1.Unmarshal(issuer.RawSubjectPublicKeyInfo, &publicKeyInfo); err != nil {
   689  		return nil, err
   690  	}
   691  
   692  	if template.IssuerHash == 0 {
   693  		template.IssuerHash = crypto.SHA1
   694  	}
   695  	hashOID := getOIDFromHashAlgorithm(template.IssuerHash)
   696  	if hashOID == nil {
   697  		return nil, errors.New("unsupported issuer hash algorithm")
   698  	}
   699  
   700  	if !template.IssuerHash.Available() {
   701  		return nil, fmt.Errorf("issuer hash algorithm %v not linked into binary", template.IssuerHash)
   702  	}
   703  	h := template.IssuerHash.New()
   704  	h.Write(publicKeyInfo.PublicKey.RightAlign())
   705  	issuerKeyHash := h.Sum(nil)
   706  
   707  	h.Reset()
   708  	h.Write(issuer.RawSubject)
   709  	issuerNameHash := h.Sum(nil)
   710  
   711  	innerResponse := singleResponse{
   712  		CertID: certID{
   713  			HashAlgorithm: pkix.AlgorithmIdentifier{
   714  				Algorithm:  hashOID,
   715  				Parameters: asn1.RawValue{Tag: 5 /* ASN.1 NULL */},
   716  			},
   717  			NameHash:      issuerNameHash,
   718  			IssuerKeyHash: issuerKeyHash,
   719  			SerialNumber:  template.SerialNumber,
   720  		},
   721  		ThisUpdate:       template.ThisUpdate.UTC(),
   722  		NextUpdate:       template.NextUpdate.UTC(),
   723  		SingleExtensions: template.ExtraExtensions,
   724  	}
   725  
   726  	switch template.Status {
   727  	case Good:
   728  		innerResponse.Good = true
   729  	case Unknown:
   730  		innerResponse.Unknown = true
   731  	case Revoked:
   732  		innerResponse.Revoked = revokedInfo{
   733  			RevocationTime: template.RevokedAt.UTC(),
   734  			Reason:         asn1.Enumerated(template.RevocationReason),
   735  		}
   736  	}
   737  
   738  	rawResponderID := asn1.RawValue{
   739  		Class:      2, // context-specific
   740  		Tag:        1, // Name (explicit tag)
   741  		IsCompound: true,
   742  		Bytes:      responderCert.RawSubject,
   743  	}
   744  	tbsResponseData := responseData{
   745  		Version:        0,
   746  		RawResponderID: rawResponderID,
   747  		ProducedAt:     time.Now().Truncate(time.Minute).UTC(),
   748  		Responses:      []singleResponse{innerResponse},
   749  	}
   750  
   751  	tbsResponseDataDER, err := asn1.Marshal(tbsResponseData)
   752  	if err != nil {
   753  		return nil, err
   754  	}
   755  
   756  	hashFunc, signatureAlgorithm, err := signingParamsForPublicKey(priv.Public(), template.SignatureAlgorithm)
   757  	if err != nil {
   758  		return nil, err
   759  	}
   760  
   761  	responseHash := hashFunc.New()
   762  	responseHash.Write(tbsResponseDataDER)
   763  	signature, err := priv.Sign(rand.Reader, responseHash.Sum(nil), hashFunc)
   764  	if err != nil {
   765  		return nil, err
   766  	}
   767  
   768  	response := basicResponse{
   769  		TBSResponseData:    tbsResponseData,
   770  		SignatureAlgorithm: signatureAlgorithm,
   771  		Signature: asn1.BitString{
   772  			Bytes:     signature,
   773  			BitLength: 8 * len(signature),
   774  		},
   775  	}
   776  	if template.Certificate != nil {
   777  		response.Certificates = []asn1.RawValue{
   778  			{FullBytes: template.Certificate.Raw},
   779  		}
   780  	}
   781  	responseDER, err := asn1.Marshal(response)
   782  	if err != nil {
   783  		return nil, err
   784  	}
   785  
   786  	return asn1.Marshal(responseASN1{
   787  		Status: asn1.Enumerated(Success),
   788  		Response: responseBytes{
   789  			ResponseType: idPKIXOCSPBasic,
   790  			Response:     responseDER,
   791  		},
   792  	})
   793  }
   794
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