/
ocsp.go
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/
ocsp.go
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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package ocsp parses OCSP responses as specified in RFC 2560. OCSP responses
// are signed messages attesting to the validity of a certificate for a small
// period of time. This is used to manage revocation for X.509 certificates.
package ocsp
import (
"crypto"
_ "crypto/sha1"
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"math/big"
"time"
)
var idPKIXOCSPBasic = asn1.ObjectIdentifier([]int{1, 3, 6, 1, 5, 5, 7, 48, 1, 1})
// These are internal structures that reflect the ASN.1 structure of an OCSP
// response. See RFC 2560, section 4.2.
const (
ocspSuccess = 0
ocspMalformed = 1
ocspInternalError = 2
ocspTryLater = 3
ocspSigRequired = 4
ocspUnauthorized = 5
)
type certID struct {
HashAlgorithm pkix.AlgorithmIdentifier
NameHash []byte
IssuerKeyHash []byte
SerialNumber *big.Int
}
type responseASN1 struct {
Status asn1.Enumerated
Response responseBytes `asn1:"explicit,tag:0"`
}
type responseBytes struct {
ResponseType asn1.ObjectIdentifier
Response []byte
}
type basicResponse struct {
TBSResponseData responseData
SignatureAlgorithm pkix.AlgorithmIdentifier
Signature asn1.BitString
Certificates []asn1.RawValue `asn1:"explicit,tag:0,optional"`
}
type responseData struct {
Raw asn1.RawContent
Version int `asn1:"optional,default:1,explicit,tag:0"`
RequestorName pkix.RDNSequence `asn1:"optional,explicit,tag:1"`
KeyHash []byte `asn1:"optional,explicit,tag:2"`
ProducedAt time.Time
Responses []singleResponse
}
type singleResponse struct {
CertID certID
Good asn1.Flag `asn1:"explicit,tag:0,optional"`
Revoked revokedInfo `asn1:"explicit,tag:1,optional"`
Unknown asn1.Flag `asn1:"explicit,tag:2,optional"`
ThisUpdate time.Time
NextUpdate time.Time `asn1:"explicit,tag:0,optional"`
}
type revokedInfo struct {
RevocationTime time.Time
Reason int `asn1:"explicit,tag:0,optional"`
}
var (
oidSignatureMD2WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 2}
oidSignatureMD5WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 4}
oidSignatureSHA1WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 5}
oidSignatureSHA256WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 11}
oidSignatureSHA384WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 12}
oidSignatureSHA512WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 13}
oidSignatureDSAWithSHA1 = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 3}
oidSignatureDSAWithSHA256 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 4, 3, 2}
oidSignatureECDSAWithSHA1 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 1}
oidSignatureECDSAWithSHA256 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 2}
oidSignatureECDSAWithSHA384 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 3}
oidSignatureECDSAWithSHA512 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 4}
)
// TODO(agl): this is taken from crypto/x509 and so should probably be exported
// from crypto/x509 or crypto/x509/pkix.
func getSignatureAlgorithmFromOID(oid asn1.ObjectIdentifier) x509.SignatureAlgorithm {
switch {
case oid.Equal(oidSignatureMD2WithRSA):
return x509.MD2WithRSA
case oid.Equal(oidSignatureMD5WithRSA):
return x509.MD5WithRSA
case oid.Equal(oidSignatureSHA1WithRSA):
return x509.SHA1WithRSA
case oid.Equal(oidSignatureSHA256WithRSA):
return x509.SHA256WithRSA
case oid.Equal(oidSignatureSHA384WithRSA):
return x509.SHA384WithRSA
case oid.Equal(oidSignatureSHA512WithRSA):
return x509.SHA512WithRSA
case oid.Equal(oidSignatureDSAWithSHA1):
return x509.DSAWithSHA1
case oid.Equal(oidSignatureDSAWithSHA256):
return x509.DSAWithSHA256
case oid.Equal(oidSignatureECDSAWithSHA1):
return x509.ECDSAWithSHA1
case oid.Equal(oidSignatureECDSAWithSHA256):
return x509.ECDSAWithSHA256
case oid.Equal(oidSignatureECDSAWithSHA384):
return x509.ECDSAWithSHA384
case oid.Equal(oidSignatureECDSAWithSHA512):
return x509.ECDSAWithSHA512
}
return x509.UnknownSignatureAlgorithm
}
// This is the exposed reflection of the internal OCSP structures.
const (
// Good means that the certificate is valid.
Good = iota
// Revoked means that the certificate has been deliberately revoked.
Revoked = iota
// Unknown means that the OCSP responder doesn't know about the certificate.
Unknown = iota
// ServerFailed means that the OCSP responder failed to process the request.
ServerFailed = iota
)
// Response represents an OCSP response. See RFC 2560.
type Response struct {
// Status is one of {Good, Revoked, Unknown, ServerFailed}
Status int
SerialNumber *big.Int
ProducedAt, ThisUpdate, NextUpdate, RevokedAt time.Time
RevocationReason int
Certificate *x509.Certificate
// TBSResponseData contains the raw bytes of the signed response. If
// Certificate is nil then this can be used to verify Signature.
TBSResponseData []byte
Signature []byte
SignatureAlgorithm x509.SignatureAlgorithm
}
// CheckSignatureFrom checks that the signature in resp is a valid signature
// from issuer. This should only be used if resp.Certificate is nil. Otherwise,
// the OCSP response contained an intermediate certificate that created the
// signature. That signature is checked by ParseResponse and only
// resp.Certificate remains to be validated.
func (resp *Response) CheckSignatureFrom(issuer *x509.Certificate) error {
return issuer.CheckSignature(resp.SignatureAlgorithm, resp.TBSResponseData, resp.Signature)
}
// ParseError results from an invalid OCSP response.
type ParseError string
func (p ParseError) Error() string {
return string(p)
}
// ParseResponse parses an OCSP response in DER form. It only supports
// responses for a single certificate. If the response contains a certificate
// then the signature over the response is checked. If issuer is not nil then
// it will be used to validate the signature or embedded certificate. Invalid
// signatures or parse failures will result in a ParseError.
func ParseResponse(bytes []byte, issuer *x509.Certificate) (*Response, error) {
var resp responseASN1
rest, err := asn1.Unmarshal(bytes, &resp)
if err != nil {
return nil, err
}
if len(rest) > 0 {
return nil, ParseError("trailing data in OCSP response")
}
ret := new(Response)
if resp.Status != ocspSuccess {
ret.Status = ServerFailed
return ret, nil
}
if !resp.Response.ResponseType.Equal(idPKIXOCSPBasic) {
return nil, ParseError("bad OCSP response type")
}
var basicResp basicResponse
rest, err = asn1.Unmarshal(resp.Response.Response, &basicResp)
if err != nil {
return nil, err
}
if len(basicResp.Certificates) > 1 {
return nil, ParseError("OCSP response contains bad number of certificates")
}
if len(basicResp.TBSResponseData.Responses) != 1 {
return nil, ParseError("OCSP response contains bad number of responses")
}
ret.TBSResponseData = basicResp.TBSResponseData.Raw
ret.Signature = basicResp.Signature.RightAlign()
ret.SignatureAlgorithm = getSignatureAlgorithmFromOID(basicResp.SignatureAlgorithm.Algorithm)
if len(basicResp.Certificates) > 0 {
ret.Certificate, err = x509.ParseCertificate(basicResp.Certificates[0].FullBytes)
if err != nil {
return nil, err
}
if err := ret.CheckSignatureFrom(ret.Certificate); err != nil {
return nil, ParseError("bad OCSP signature")
}
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")
}
}
} else if issuer != nil {
if err := ret.CheckSignatureFrom(issuer); err != nil {
return nil, ParseError("bad OCSP signature")
}
}
r := basicResp.TBSResponseData.Responses[0]
ret.SerialNumber = r.CertID.SerialNumber
switch {
case bool(r.Good):
ret.Status = Good
case bool(r.Unknown):
ret.Status = Unknown
default:
ret.Status = Revoked
ret.RevokedAt = r.Revoked.RevocationTime
ret.RevocationReason = r.Revoked.Reason
}
ret.ProducedAt = basicResp.TBSResponseData.ProducedAt
ret.ThisUpdate = r.ThisUpdate
ret.NextUpdate = r.NextUpdate
return ret, nil
}
// https://tools.ietf.org/html/rfc2560#section-4.1.1
type ocspRequest struct {
TBSRequest tbsRequest
}
type tbsRequest struct {
Version int `asn1:"explicit,tag:0,default:0"`
RequestList []request
}
type request struct {
Cert certID
}
// RequestOptions contains options for constructing OCSP requests.
type RequestOptions struct {
// Hash contains the hash function that should be used when
// constructing the OCSP request. If zero, SHA-1 will be used.
Hash crypto.Hash
}
func (opts *RequestOptions) hash() crypto.Hash {
if opts == nil || opts.Hash == 0 {
// SHA-1 is nearly universally used in OCSP.
return crypto.SHA1
}
return opts.Hash
}
// CreateRequest returns a DER-encoded, OCSP request for the status of cert. If
// opts is nil then sensible defaults are used.
func CreateRequest(cert, issuer *x509.Certificate, opts *RequestOptions) ([]byte, error) {
hashFunc := opts.hash()
// OCSP seems to be the only place where these raw hash identifiers are
// used. I took the following from
// http://msdn.microsoft.com/en-us/library/ff635603.aspx
var hashOID asn1.ObjectIdentifier
switch hashFunc {
case crypto.SHA1:
hashOID = asn1.ObjectIdentifier([]int{1, 3, 14, 3, 2, 26})
case crypto.SHA256:
hashOID = asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 1})
case crypto.SHA384:
hashOID = asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 2})
case crypto.SHA512:
hashOID = asn1.ObjectIdentifier([]int{2, 16, 840, 1, 101, 3, 4, 2, 3})
default:
return nil, x509.ErrUnsupportedAlgorithm
}
if !hashFunc.Available() {
return nil, x509.ErrUnsupportedAlgorithm
}
h := opts.hash().New()
var publicKeyInfo struct {
Algorithm pkix.AlgorithmIdentifier
PublicKey asn1.BitString
}
if _, err := asn1.Unmarshal(issuer.RawSubjectPublicKeyInfo, &publicKeyInfo); err != nil {
return nil, err
}
h.Write(publicKeyInfo.PublicKey.RightAlign())
issuerKeyHash := h.Sum(nil)
h.Reset()
h.Write(issuer.RawSubject)
issuerNameHash := h.Sum(nil)
return asn1.Marshal(ocspRequest{
tbsRequest{
Version: 0,
RequestList: []request{
{
Cert: certID{
pkix.AlgorithmIdentifier{
Algorithm: hashOID,
Parameters: asn1.RawValue{Tag: 5 /* ASN.1 NULL */},
},
issuerNameHash,
issuerKeyHash,
cert.SerialNumber,
},
},
},
},
})
}