crypto/tls: remove RSA KEX ciphers from the default list

[gostls13.git] / src / crypto / tls / cipher_suites.go

diff --git a/src/crypto/tls/cipher_suites.go b/src/crypto/tls/cipher_suites.go
index 3f976c9c58b7f307280b9f78c3f602865240ec15..eaeb7e04e6ccfdd118823151c375c9a50d00dd44 100644 (file)
--- a/src/crypto/tls/cipher_suites.go
+++ b/src/crypto/tls/cipher_suites.go
@@ -17,6 +17,7 @@ import (
        "fmt"
        "hash"
        "internal/cpu"
+       "internal/godebug"
        "runtime"
 
        "golang.org/x/crypto/chacha20poly1305"
@@ -335,10 +336,35 @@ var disabledCipherSuites = []uint16{
 }
 
 var (
-       defaultCipherSuitesLen = len(cipherSuitesPreferenceOrder) - len(disabledCipherSuites)
-       defaultCipherSuites    = cipherSuitesPreferenceOrder[:defaultCipherSuitesLen]
+       defaultCipherSuitesLen int
+       defaultCipherSuites    []uint16
 )
 
+// rsaKexCiphers contains the ciphers which use RSA based key exchange,
+// which we disable by default.
+var rsaKexCiphers = map[uint16]bool{
+       TLS_RSA_WITH_RC4_128_SHA:        true,
+       TLS_RSA_WITH_3DES_EDE_CBC_SHA:   true,
+       TLS_RSA_WITH_AES_128_CBC_SHA:    true,
+       TLS_RSA_WITH_AES_256_CBC_SHA:    true,
+       TLS_RSA_WITH_AES_128_CBC_SHA256: true,
+       TLS_RSA_WITH_AES_128_GCM_SHA256: true,
+       TLS_RSA_WITH_AES_256_GCM_SHA384: true,
+}
+
+var rsaKEXgodebug = godebug.New("tlsrsakex")
+
+func init() {
+       rsaKexEnabled := rsaKEXgodebug.Value() == "1"
+       for _, c := range cipherSuitesPreferenceOrder[:len(cipherSuitesPreferenceOrder)-len(disabledCipherSuites)] {
+               if !rsaKexEnabled && rsaKexCiphers[c] {
+                       continue
+               }
+               defaultCipherSuites = append(defaultCipherSuites, c)
+       }
+       defaultCipherSuitesLen = len(defaultCipherSuites)
+}
+
 // defaultCipherSuitesTLS13 is also the preference order, since there are no
 // disabled by default TLS 1.3 cipher suites. The same AES vs ChaCha20 logic as
 // cipherSuitesPreferenceOrder applies.