From fffb189cb543f51e3db21be9c22d91d2cf3be363 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Mon, 11 Mar 2019 15:01:47 +0900
Subject: [PATCH] use ChaCha if one of the peers doesn't have AES hardware
 support

---
 crypto.go    | 33 +++++++++++++++++++++++++++++----
 go.mod       |  2 +-
 package.json |  6 ++++++
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/crypto.go b/crypto.go
index 2b9cd52..c0ac657 100644
--- a/crypto.go
+++ b/crypto.go
@@ -13,6 +13,8 @@ import (
 	"math/big"
 	"time"
 
+	"golang.org/x/sys/cpu"
+
 	crypto "github.com/libp2p/go-libp2p-crypto"
 	ic "github.com/libp2p/go-libp2p-crypto"
 	peer "github.com/libp2p/go-libp2p-peer"
@@ -40,10 +42,11 @@ func NewIdentity(privKey ic.PrivKey) (*Identity, error) {
 	}
 	return &Identity{
 		config: tls.Config{
-			MinVersion:         tls.VersionTLS13,
-			InsecureSkipVerify: true, // This is not insecure here. We will verify the cert chain ourselves.
-			ClientAuth:         tls.RequireAnyClientCert,
-			Certificates:       []tls.Certificate{*cert},
+			MinVersion:               tls.VersionTLS13,
+			PreferServerCipherSuites: preferServerCipherSuites(),
+			InsecureSkipVerify:       true, // This is not insecure here. We will verify the cert chain ourselves.
+			ClientAuth:               tls.RequireAnyClientCert,
+			Certificates:             []tls.Certificate{*cert},
 			VerifyPeerCertificate: func(_ [][]byte, _ [][]*x509.Certificate) error {
 				panic("tls config not specialized for peer")
 			},
@@ -194,3 +197,25 @@ func keyToCertificate(sk ic.PrivKey) (*tls.Certificate, error) {
 		PrivateKey:  certKey,
 	}, nil
 }
+
+// We want nodes without AES hardware (e.g. ARM) support to always use ChaCha.
+// Only if both nodes have AES hardware support (e.g. x86), AES should be used.
+// x86->x86: AES, ARM->x86: ChaCha, x86->ARM: ChaCha and ARM->ARM: Chacha
+// This function returns true if we don't have AES hardware support, and false otherwise.
+// Thus, ARM servers will always use their own cipher suite preferences (ChaCha first),
+// and x86 servers will aways use the client's cipher suite preferences.
+func preferServerCipherSuites() bool {
+	// Copied from the Go TLS implementation.
+
+	// Check the cpu flags for each platform that has optimized GCM implementations.
+	// Worst case, these variables will just all be false.
+	var (
+		hasGCMAsmAMD64 = cpu.X86.HasAES && cpu.X86.HasPCLMULQDQ
+		hasGCMAsmARM64 = cpu.ARM64.HasAES && cpu.ARM64.HasPMULL
+		// Keep in sync with crypto/aes/cipher_s390x.go.
+		hasGCMAsmS390X = cpu.S390X.HasAES && cpu.S390X.HasAESCBC && cpu.S390X.HasAESCTR && (cpu.S390X.HasGHASH || cpu.S390X.HasAESGCM)
+
+		hasGCMAsm = hasGCMAsmAMD64 || hasGCMAsmARM64 || hasGCMAsmS390X
+	)
+	return !hasGCMAsm
+}
diff --git a/go.mod b/go.mod
index d1a70ad..30340cc 100644
--- a/go.mod
+++ b/go.mod
@@ -13,7 +13,7 @@ require (
 	golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2 // indirect
 	golang.org/x/net v0.0.0-20190310074541-c10a0554eabf // indirect
 	golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6 // indirect
-	golang.org/x/sys v0.0.0-20190310054646-10058d7d4faa // indirect
+	golang.org/x/sys v0.0.0-20190310054646-10058d7d4faa
 	golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2 // indirect
 	gopkg.in/yaml.v2 v2.2.2 // indirect
 )
diff --git a/package.json b/package.json
index 2bc7d04..19d87a0 100644
--- a/package.json
+++ b/package.json
@@ -12,6 +12,12 @@
       "hash": "QmbyjEKtxXmZdiByBiNhfayzEuEPPBvuD2dLpHky8cHUvy",
       "name": "go-conn-security",
       "version": "0.1.20"
+    },
+    {
+      "author": "marten-seemann",
+      "hash": "QmauyZ2BbYbcTJr1RudEsbQoKNgKkZi9pDZBJVyzw3uJD4",
+      "name": "cpu",
+      "version": "0.1.0"
     }
   ],
   "gxVersion": "0.12.1",