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crypto/tls: implement X25519MLKEM768

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This makes three related changes that work particularly well together
and would require significant extra work to do separately: it replaces
X25519Kyber768Draft00 with X25519MLKEM768, it makes CurvePreferences
ordering crypto/tls-selected, and applies a preference to PQ key
exchange methods over key shares (to mitigate downgrades).

TestHandshakeServerUnsupportedKeyShare was removed because we are not
rejecting unsupported key shares anymore (nor do we select them, and
rejecting them actively is a MAY). It would have been nice to keep the
test to check we still continue successfully, but testClientHelloFailure
is broken in the face of any server-side behavior which requires writing
any other messages back to the client, or reading them.

Updates #69985
Fixes #69393

Change-Id: I58de76f5b8742a9bd4543fd7907c48e038507b19
Reviewed-on: https://go-review.googlesource.com/c/go/+/630775
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Filippo Valsorda 2024-11-21 21:21:58 +01:00 • committed by Gopher Robot
parent 68e64cfceb
commit 77ea502eee
14 changed files with 177 additions and 206 deletions
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29
handshake_client_tls13.go
View file

@ -322,12 +322,11 @@ func (hs *clientHandshakeStateTLS13) processHelloRetryRequest() error {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: server sent an unnecessary HelloRetryRequest key_share")
}
// Note: we don't support selecting X25519Kyber768Draft00 in a HRR,
// because we currently only support it at all when CurvePreferences is
// empty, which will cause us to also send a key share for it.
// Note: we don't support selecting X25519MLKEM768 in a HRR, because it
// is currently first in preference order, so if it's enabled we'll
// always send a key share for it.
//
// This will have to change once we support selecting hybrid KEMs
// without sending key shares for them.
// This will have to change once we support multiple hybrid KEMs.
if _, ok := curveForCurveID(curveID); !ok {
c.sendAlert(alertInternalError)
return errors.New("tls: CurvePreferences includes unsupported curve")
@ -480,12 +479,12 @@ func (hs *clientHandshakeStateTLS13) establishHandshakeKeys() error {
c := hs.c
ecdhePeerData := hs.serverHello.serverShare.data
if hs.serverHello.serverShare.group == x25519Kyber768Draft00 {
if len(ecdhePeerData) != x25519PublicKeySize+mlkem.CiphertextSize768 {
if hs.serverHello.serverShare.group == X25519MLKEM768 {
if len(ecdhePeerData) != mlkem.CiphertextSize768+x25519PublicKeySize {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: invalid server key share")
return errors.New("tls: invalid server X25519MLKEM768 key share")
}
ecdhePeerData = hs.serverHello.serverShare.data[:x25519PublicKeySize]
ecdhePeerData = hs.serverHello.serverShare.data[mlkem.CiphertextSize768:]
}
peerKey, err := hs.keyShareKeys.ecdhe.Curve().NewPublicKey(ecdhePeerData)
if err != nil {
@ -497,17 +496,17 @@ func (hs *clientHandshakeStateTLS13) establishHandshakeKeys() error {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: invalid server key share")
}
if hs.serverHello.serverShare.group == x25519Kyber768Draft00 {
if hs.keyShareKeys.kyber == nil {
if hs.serverHello.serverShare.group == X25519MLKEM768 {
if hs.keyShareKeys.mlkem == nil {
return c.sendAlert(alertInternalError)
}
ciphertext := hs.serverHello.serverShare.data[x25519PublicKeySize:]
kyberShared, err := kyberDecapsulate(hs.keyShareKeys.kyber, ciphertext)
ciphertext := hs.serverHello.serverShare.data[:mlkem.CiphertextSize768]
mlkemShared, err := hs.keyShareKeys.mlkem.Decapsulate(ciphertext)
if err != nil {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: invalid Kyber server key share")
return errors.New("tls: invalid X25519MLKEM768 server key share")
}
sharedKey = append(sharedKey, kyberShared...)
sharedKey = append(mlkemShared, sharedKey...)
}
c.curveID = hs.serverHello.serverShare.group