Query a roughtime server to mitigate NTP attacks (#3151)

WORKSPACE

@@ -1260,3 +1260,16 @@ go_repository(
     commit = "11bc5ee7ad5de4bf1380f3103eebdd40db99a666",
     importpath = "github.com/prysmaticlabs/ethereumapis",
 )
+
+go_repository(
+    name = "com_github_cloudflare_roughtime",
+    commit = "6b7e31ac9cb2d6048096585d2e8563ee60b28f84",
+    importpath = "github.com/cloudflare/roughtime",
+)
+
+go_repository(
+    name = "com_googlesource_roughtime_roughtime_git",
+    build_file_generation = "on",
+    commit = "51f6971f5f06ec101e5fbcabe5a49477708540f3",
+    importpath = "roughtime.googlesource.com/roughtime.git",
+)

shared/roughtime/BUILD.bazel

@@ -0,0 +1,12 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["roughtime.go"],
+    importpath = "github.com/prysmaticlabs/prysm/shared/roughtime",
+    visibility = ["//visibility:public"],
+    deps = [
+        "@com_github_cloudflare_roughtime//:go_default_library",
+        "@com_googlesource_roughtime_roughtime_git//go/config:go_default_library",
+    ],
+)

shared/roughtime/roughtime.go

@@ -0,0 +1,86 @@
+// Package roughtime is a wrapper for a roughtime clock source
+package roughtime
+
+import (
+	"encoding/base64"
+	"time"
+
+	rt "github.com/cloudflare/roughtime"
+	"roughtime.googlesource.com/roughtime.git/go/config"
+)
+
+// offset is the difference between the system time and the time returned by
+// the roughtime server
+var offset time.Duration
+
+// Decode or panic
+func mustDecodeString(in string) []byte {
+	pk, err := base64.StdEncoding.DecodeString(in)
+	if err != nil {
+		panic(err)
+	}
+	return pk
+}
+
+func init() {
+	t0 := time.Now()
+
+	// A list of reliable roughtime servers with their public keys.
+	// From https://github.com/cloudflare/roughtime/blob/master/ecosystem.json
+	servers := []config.Server{
+		{
+			Name:          "Caesium",
+			PublicKeyType: "ed25519",
+			PublicKey:     mustDecodeString("iBVjxg/1j7y1+kQUTBYdTabxCppesU/07D4PMDJk2WA="),
+			Addresses: []config.ServerAddress{
+				{
+					Protocol: "udp",
+					Address:  "caesium.tannerryan.ca:2002",
+				},
+			},
+		},
+		{
+			Name:          "Chainpoint-Roughtime",
+			PublicKeyType: "ed25519",
+			PublicKey:     mustDecodeString("bbT+RPS7zKX6w71ssPibzmwWqU9ffRV5oj2OresSmhE="),
+			Addresses: []config.ServerAddress{
+				{
+					Protocol: "udp",
+					Address:  "roughtime.chainpoint.org:2002",
+				},
+			},
+		},
+		{
+			Name:          "Cloudflare-Roughtime",
+			PublicKeyType: "ed25519",
+			PublicKey:     mustDecodeString("gD63hSj3ScS+wuOeGrubXlq35N1c5Lby/S+T7MNTjxo="),
+			Addresses: []config.ServerAddress{
+				{
+					Protocol: "udp",
+					Address:  "roughtime.cloudflare.com:2002",
+				},
+			},
+		},
+	}
+
+	results := rt.Do(servers, rt.DefaultQueryAttempts, rt.DefaultQueryTimeout, nil)
+
+	// Compute the average difference between the system's time and the
+	// Roughtime responses from the servers, rejecting responses whose radii
+	// are larger than 2 seconds.
+	var err error
+	offset, err = rt.AvgDeltaWithRadiusThresh(results, t0, 2*time.Second)
+	if err != nil {
+		panic(err)
+	}
+}
+
+// Since returns the duration since t, based on the roughtime response
+func Since(t time.Time) time.Duration {
+	return time.Now().Add(offset).Sub(t)
+}
+
+// Until returns the duration until t, based on the roughtime response
+func Until(t time.Time) time.Duration {
+	return t.Sub(time.Now().Add(offset))
+}

shared/slotutil/BUILD.bazel

@@ -5,6 +5,7 @@ go_library(
     srcs = ["slotticker.go"],
     importpath = "github.com/prysmaticlabs/prysm/shared/slotutil",
     visibility = ["//visibility:public"],
+    deps = ["//shared/roughtime:go_default_library"],
 )
 
 go_test(

shared/slotutil/slotticker.go

@@ -2,6 +2,8 @@ package slotutil
 
 import (
 	"time"
+
+	"github.com/prysmaticlabs/prysm/shared/roughtime"
 )
 
 // SlotTicker is a special ticker for the beacon chain block.
@@ -34,7 +36,7 @@ func GetSlotTicker(genesisTime time.Time, secondsPerSlot uint64) *SlotTicker {
 		c:    make(chan uint64),
 		done: make(chan struct{}),
 	}
-	ticker.start(genesisTime, secondsPerSlot, time.Since, time.Until, time.After)
+	ticker.start(genesisTime, secondsPerSlot, roughtime.Since, roughtime.Until, time.After)
 	return ticker
 }