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crypto/tls: implement TLS 1.3 version negotiation

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RFC 8446 recommends using the supported_versions extension to negotiate
lower versions as well, so begin by implementing it to negotiate the
currently supported versions.

Note that pickTLSVersion was incorrectly negotiating the ServerHello
version down on the client. If the server had illegally sent a version
higher than the ClientHello version, the client would have just
downgraded it, hopefully failing later in the handshake.

In TestGetConfigForClient, we were hitting the record version check
because the server would select TLS 1.1, the handshake would fail on the
client which required TLS 1.2, which would then send a TLS 1.0 record
header on its fatal alert (not having negotiated a version), while the
server would expect a TLS 1.1 header at that point. Now, the client gets
to communicate the minimum version through the extension and the
handshake fails on the server.

Updates #9671

Change-Id: Ie33c7124c0c769f62e10baad51cbed745c424e5b
Reviewed-on: https://go-review.googlesource.com/c/146217
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
This commit is contained in:
Filippo Valsorda 2018-10-31 09:34:10 -04:00
parent d4e9432552
commit 6d1d147e90
5 changed files with 100 additions and 46 deletions
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67
common.go
View file

@ -39,9 +39,6 @@ const (
recordHeaderLen = 5 // record header length
maxHandshake = 65536 // maximum handshake we support (protocol max is 16 MB)
maxUselessRecords = 5 // maximum number of consecutive non-advancing records
minVersion = VersionTLS10
maxVersion = VersionTLS12
)
// TLS record types.
@ -714,18 +711,43 @@ func (c *Config) cipherSuites() []uint16 {
return s
}
func (c *Config) minVersion() uint16 {
if c == nil || c.MinVersion == 0 {
return minVersion
}
return c.MinVersion
var supportedVersions = []uint16{
VersionTLS12,
VersionTLS11,
VersionTLS10,
VersionSSL30,
}
func (c *Config) maxVersion() uint16 {
if c == nil || c.MaxVersion == 0 {
return maxVersion
func (c *Config) supportedVersions(isClient bool) []uint16 {
versions := make([]uint16, 0, len(supportedVersions))
for _, v := range supportedVersions {
if c != nil && c.MinVersion != 0 && v < c.MinVersion {
continue
}
if c != nil && c.MaxVersion != 0 && v > c.MaxVersion {
continue
}
// TLS 1.0 is the minimum version supported as a client.
if isClient && v < VersionTLS10 {
continue
}
versions = append(versions, v)
}
return c.MaxVersion
return versions
}
// supportedVersionsFromMax returns a list of supported versions derived from a
// legacy maximum version value. Note that only versions supported by this
// library are returned. Any newer peer will use supportedVersions anyway.
func supportedVersionsFromMax(maxVersion uint16) []uint16 {
versions := make([]uint16, 0, len(supportedVersions))
for _, v := range supportedVersions {
if v > maxVersion {
continue
}
versions = append(versions, v)
}
return versions
}
var defaultCurvePreferences = []CurveID{X25519, CurveP256, CurveP384, CurveP521}
@ -738,18 +760,17 @@ func (c *Config) curvePreferences() []CurveID {
}
// mutualVersion returns the protocol version to use given the advertised
// version of the peer.
func (c *Config) mutualVersion(vers uint16) (uint16, bool) {
minVersion := c.minVersion()
maxVersion := c.maxVersion()
if vers < minVersion {
return 0, false
// versions of the peer. Priority is given to the peer preference order.
func (c *Config) mutualVersion(isClient bool, peerVersions []uint16) (uint16, bool) {
supportedVersions := c.supportedVersions(isClient)
for _, peerVersion := range peerVersions {
for _, v := range supportedVersions {
if v == peerVersion {
return v, true
}
}
}
if vers > maxVersion {
vers = maxVersion
}
return vers, true
return 0, false
}
// getCertificate returns the best certificate for the given ClientHelloInfo,