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crypto/tls: add GetClientCertificate callback

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Currently, the selection of a client certificate done internally based
on the limitations given by the server's request and the certifcates in
the Config. This means that it's not possible for an application to
control that selection based on details of the request.

This change adds a callback, GetClientCertificate, that is called by a
Client during the handshake and which allows applications to select the
best certificate at that time.

(Based on https://golang.org/cl/25570/ by Bernd Fix.)

Fixes #16626.

Change-Id: Ia4cea03235d2aa3c9fd49c99c227593c8e86ddd9
Reviewed-on: https://go-review.googlesource.com/32115
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Adam Langley 2016-10-26 10:05:03 -07:00
parent 97a4987572
commit 0b375e2be0
4 changed files with 287 additions and 73 deletions
Download patch file Download diff file Expand all files Collapse all files

185
handshake_client.go
View file

@ -199,7 +199,7 @@ NextCipherSuite:
// Otherwise, in a full handshake, if we don't have any certificates
// configured then we will never send a CertificateVerify message and
// thus no signatures are needed in that case either.
if isResume || len(c.config.Certificates) == 0 {
if isResume || (len(c.config.Certificates) == 0 && c.config.GetClientCertificate == nil) {
hs.finishedHash.discardHandshakeBuffer()
}
@ -377,71 +377,11 @@ func (hs *clientHandshakeState) doFullHandshake() error {
certReq, ok := msg.(*certificateRequestMsg)
if ok {
certRequested = true
// RFC 4346 on the certificateAuthorities field:
// A list of the distinguished names of acceptable certificate
// authorities. These distinguished names may specify a desired
// distinguished name for a root CA or for a subordinate CA;
// thus, this message can be used to describe both known roots
// and a desired authorization space. If the
// certificate_authorities list is empty then the client MAY
// send any certificate of the appropriate
// ClientCertificateType, unless there is some external
// arrangement to the contrary.
hs.finishedHash.Write(certReq.marshal())
var rsaAvail, ecdsaAvail bool
for _, certType := range certReq.certificateTypes {
switch certType {
case certTypeRSASign:
rsaAvail = true
case certTypeECDSASign:
ecdsaAvail = true
}
}
// We need to search our list of client certs for one
// where SignatureAlgorithm is acceptable to the server and the
// Issuer is in certReq.certificateAuthorities
findCert:
for i, chain := range c.config.Certificates {
if !rsaAvail && !ecdsaAvail {
continue
}
for j, cert := range chain.Certificate {
x509Cert := chain.Leaf
// parse the certificate if this isn't the leaf
// node, or if chain.Leaf was nil
if j != 0 || x509Cert == nil {
if x509Cert, err = x509.ParseCertificate(cert); err != nil {
c.sendAlert(alertInternalError)
return errors.New("tls: failed to parse client certificate #" + strconv.Itoa(i) + ": " + err.Error())
}
}
switch {
case rsaAvail && x509Cert.PublicKeyAlgorithm == x509.RSA:
case ecdsaAvail && x509Cert.PublicKeyAlgorithm == x509.ECDSA:
default:
continue findCert
}
if len(certReq.certificateAuthorities) == 0 {
// they gave us an empty list, so just take the
// first cert from c.config.Certificates
chainToSend = &chain
break findCert
}
for _, ca := range certReq.certificateAuthorities {
if bytes.Equal(x509Cert.RawIssuer, ca) {
chainToSend = &chain
break findCert
}
}
}
if chainToSend, err = hs.getCertificate(certReq); err != nil {
c.sendAlert(alertInternalError)
return err
}
msg, err = c.readHandshake()
@ -462,9 +402,7 @@ func (hs *clientHandshakeState) doFullHandshake() error {
// certificate to send.
if certRequested {
certMsg = new(certificateMsg)
if chainToSend != nil {
certMsg.certificates = chainToSend.Certificate
}
certMsg.certificates = chainToSend.Certificate
hs.finishedHash.Write(certMsg.marshal())
if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
return err
@ -483,7 +421,7 @@ func (hs *clientHandshakeState) doFullHandshake() error {
}
}
if chainToSend != nil {
if chainToSend != nil && len(chainToSend.Certificate) > 0 {
certVerify := &certificateVerifyMsg{
hasSignatureAndHash: c.vers >= VersionTLS12,
}
@ -727,6 +665,117 @@ func (hs *clientHandshakeState) sendFinished(out []byte) error {
return nil
}
// tls11SignatureSchemes contains the signature schemes that we synthesise for
// a TLS <= 1.1 connection, based on the supported certificate types.
var tls11SignatureSchemes = []SignatureScheme{ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1}
const (
// tls11SignatureSchemesNumECDSA is the number of initial elements of
// tls11SignatureSchemes that use ECDSA.
tls11SignatureSchemesNumECDSA = 3
// tls11SignatureSchemesNumRSA is the number of trailing elements of
// tls11SignatureSchemes that use RSA.
tls11SignatureSchemesNumRSA = 4
)
func (hs *clientHandshakeState) getCertificate(certReq *certificateRequestMsg) (*Certificate, error) {
c := hs.c
var rsaAvail, ecdsaAvail bool
for _, certType := range certReq.certificateTypes {
switch certType {
case certTypeRSASign:
rsaAvail = true
case certTypeECDSASign:
ecdsaAvail = true
}
}
if c.config.GetClientCertificate != nil {
var signatureSchemes []SignatureScheme
if !certReq.hasSignatureAndHash {
// Prior to TLS 1.2, the signature schemes were not
// included in the certificate request message. In this
// case we use a plausible list based on the acceptable
// certificate types.
signatureSchemes = tls11SignatureSchemes
if !ecdsaAvail {
signatureSchemes = signatureSchemes[tls11SignatureSchemesNumECDSA:]
}
if !rsaAvail {
signatureSchemes = signatureSchemes[:len(signatureSchemes)-tls11SignatureSchemesNumRSA]
}
} else {
signatureSchemes = make([]SignatureScheme, 0, len(certReq.signatureAndHashes))
for _, sah := range certReq.signatureAndHashes {
signatureSchemes = append(signatureSchemes, SignatureScheme(sah.hash)<<8+SignatureScheme(sah.signature))
}
}
return c.config.GetClientCertificate(&CertificateRequestInfo{
AcceptableCAs: certReq.certificateAuthorities,
SignatureSchemes: signatureSchemes,
})
}
// RFC 4346 on the certificateAuthorities field: A list of the
// distinguished names of acceptable certificate authorities.
// These distinguished names may specify a desired
// distinguished name for a root CA or for a subordinate CA;
// thus, this message can be used to describe both known roots
// and a desired authorization space. If the
// certificate_authorities list is empty then the client MAY
// send any certificate of the appropriate
// ClientCertificateType, unless there is some external
// arrangement to the contrary.
// We need to search our list of client certs for one
// where SignatureAlgorithm is acceptable to the server and the
// Issuer is in certReq.certificateAuthorities
findCert:
for i, chain := range c.config.Certificates {
if !rsaAvail && !ecdsaAvail {
continue
}
for j, cert := range chain.Certificate {
x509Cert := chain.Leaf
// parse the certificate if this isn't the leaf
// node, or if chain.Leaf was nil
if j != 0 || x509Cert == nil {
var err error
if x509Cert, err = x509.ParseCertificate(cert); err != nil {
c.sendAlert(alertInternalError)
return nil, errors.New("tls: failed to parse client certificate #" + strconv.Itoa(i) + ": " + err.Error())
}
}
switch {
case rsaAvail && x509Cert.PublicKeyAlgorithm == x509.RSA:
case ecdsaAvail && x509Cert.PublicKeyAlgorithm == x509.ECDSA:
default:
continue findCert
}
if len(certReq.certificateAuthorities) == 0 {
// they gave us an empty list, so just take the
// first cert from c.config.Certificates
return &chain, nil
}
for _, ca := range certReq.certificateAuthorities {
if bytes.Equal(x509Cert.RawIssuer, ca) {
return &chain, nil
}
}
}
}
// No acceptable certificate found. Don't send a certificate.
return new(Certificate), nil
}
// clientSessionCacheKey returns a key used to cache sessionTickets that could
// be used to resume previously negotiated TLS sessions with a server.
func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {