Almost done with DHT

README.md

@@ -16,7 +16,7 @@ Alright, let's solve all those problems above with Kela! Kela consists of three
 
 ### Name resolution service
 
-In Kela, each user has an ID, which is a public key. Each user is associated with one or more Kela servers, which store that user's data. To find out which servers a user is associated with, you can query the name resolution system. All Kela servers participate in the name resolution system and act as DHT nodes. Each server stores a complete list of all DHT nodes. When a new server joins the DHT, it tries to peer with an existing server in the DHT. Say server `example.com` would like to peer with `test.net`. `example.com` first sends a GET request to `test.net/peer?peer=example.com`. `test.net` replies with its list of DHT nodes. Once `example.com` receives this reply, it adds `test.net` to its list of DHT nodes and attempts to peer with all servers in the reply that it hasn't peered with yet. `test.net` now also tries to peer with the server that just contacted it, in this case `example.com`. Servers periodically go through their list of DHT nodes and remove nodes that are no longer online.
+In Kela, each user has an ID, which is an Ed5519 public key encoded in URL-safe Base64. Each user is associated with one or more Kela servers, which store that user's data. To find out which servers a user is associated with, you can query the name resolution system. All Kela servers participate in the name resolution system and act as DHT nodes. Each server stores a complete list of all DHT nodes. When a new server joins the DHT, it tries to peer with an existing server in the DHT. Say server `example.com` would like to peer with `test.net`. `example.com` first sends a GET request to `test.net/peer?peer=example.com`. `test.net` replies with its list of DHT nodes. Once `example.com` receives this reply, it adds `test.net` to its list of DHT nodes and attempts to peer with all servers in the reply that it hasn't peered with yet. `test.net` now also tries to peer with the server that just contacted it, in this case `example.com`. Servers periodically go through their list of DHT nodes and remove nodes that are no longer online.
 
 The DHT stores key-value pairs. The key consists of a user's public key and timestamp (the current Unix time in seconds divided by 600, rounded down). The value consists of a timestamp (the current Unix time in seconds), a list of servers that the user is associated with, where the first server is their primary server, and a signature. A key-value pair is assigned to the 5 servers with smallest SHA-256 hashes of their domain name greater than the SHA-256 hash of the key. The purpose of the elaborate timestamp in the key is to ensure that the set of servers assigned to a key-value pair rotates every 600 seconds so an attacker must control a very large portion of the DHT to do a denial-of-service attack against a specific key-value pair. When servers join and leave the DHT, the servers that a user is associated with will ensure that that user's key-value pair is assigned to a new server if necessary to ensure that 5 servers store that key-value pair. The DHT supports two operations, get and put. For put operations, the server checks the signature to ensure the validity of the request. When a server receives either of these two operations, it computes the SHA-256 hash of the key and checks if it is supposed to store that key-value pair or not. If it is supposed to store that key-value pair, it performs the operation on that pair. Otherwise, the server will contact in parallel the 5 servers that store this key-value pair. If the operation is a get, the server will look at the 5 replies and return the value with the most recent timestamp. If the operation is a put, and one of the 5 parallel requests fails, the server will remove that offline server from its DHT node list and assign a new server to this key-value pair to replace the offline one. Each server periodically goes through its stored key-value pairs and deletes old ones.
 

server/dht.go

@@ -1,16 +1,27 @@
 package main
 
 import (
-	"crypto/ed25519"
+	"bytes"
+	"crypto/sha256"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io"
 	"log"
 	"net/http"
 	"sort"
+	"strconv"
 	"strings"
+	"sync"
+	"time"
 )
 
+// Get the sha256sum of string as a URL-safe unpadded base64 string
+func sha256sum(s string) string {
+	b := sha256.Sum256([]byte(s))
+	return base64.RawURLEncoding.EncodeToString(b[:])
+}
+
 // Try to peer with another server
 func addPeer(peer string) error {
 	peerHash := sha256sum(peer)
@@ -71,69 +82,123 @@ func peerHandler(w http.ResponseWriter, r *http.Request) {
 	go addPeer(peer)
 }
 
-// Handle DHT requests
-func dhtHandler(w http.ResponseWriter, r *http.Request) {
-	key := r.URL.String()[5:]
-	keyHash := sha256sum(key)
-	pubKey := asPubKey(key)
-	fmt.Println(key, keyHash, pubKey)
-	mu.Lock()
-	keyPos := sort.SearchStrings(peerHashes, keyHash)
+// Find the position of a key in the DHT
+func keyPos(key string) int {
+	keyPos := sort.SearchStrings(peerHashes, sha256sum(key))
 	if keyPos < myPos {
 		keyPos += len(peerHashes)
 	}
-	mu.Unlock()
-	if r.Method == "GET" {
-		if keyPos - myPos < 5 {
-			mu.Lock()
-			if val, ok := kvstore[key]; ok {
-				w.Write([]byte(val))
-			} else {
-				w.WriteHeader(http.StatusNotFound)
+	return keyPos
+}
+
+
+// Get the value for a key from the DHT
+func dhtGet(key string) ([]byte, error) {
+	keyPos := keyPos(key)
+	var wg sync.WaitGroup
+	var ret []byte
+	bestTime := 0
+	for i := 0; i < 5 && i < len(peerHashes); i++ {
+		wg.Add(1)
+		j := hashToDomain[peerHashes[(keyPos+i)%len(peerHashes)]]
+		go func() {
+			defer wg.Done()
+			resp, err := http.Get(j + "/dht/" + key + "?direct")
+			if err != nil {
+				// TODO: Remove this server from DHT?
+				// For sanity reasons this might be a bad idea
+				return
 			}
-			mu.Unlock()
-		} else {
-			for i := 0; i < 5 && i < len(peerHashes); i++ {
-				j := hashToDomain[peerHashes[(keyPos+i)%len(peerHashes)]]
-				go func() string {
-					resp, err := http.Get(j + r.URL.String())
-					if err != nil {
-						return ""
-					}
-					b, err := io.ReadAll(resp.Body)
-					if err != nil {
-						return ""
-					}
-					return string(b)
-				}()
-
+			b, err := io.ReadAll(resp.Body)
+			if err != nil {
+				return
 			}
+			err = verify(key, b)
+			if err != nil {
+				return
+			}
+			valTime, err := strconv.Atoi(strings.Split(string(b), "\n")[0])
+			if err != nil {
+				return
+			}
+			if ret == nil || valTime > bestTime {
+				ret = b
+				bestTime = valTime
+			}
+		}()
+	}
+	wg.Wait()
+	if ret == nil {
+		return nil, errors.New("id not in kvstore")
+	}
+	return ret, nil
+}
 
+// Put a key-value pair into the DHT
+func dhtPut(key string, val []byte) error {
+	err := verify(key, val)
+	if err != nil {
+		return err
+	}
+	keyPos := keyPos(key)
+	for i := 0; i < 5 && i < len(peerHashes); i++ {
+		j := hashToDomain[peerHashes[(keyPos+i)%len(peerHashes)]]
+		go func() {
+			http.Post(j + "/dht/" + key + "?direct", "application/octet-stream", bytes.NewBuffer(val))
+		}()
+	}
+	return nil
+}
 
+// Handle DHT requests
+func dhtHandler(w http.ResponseWriter, r *http.Request) {
+	key := r.URL.Path[5:]
+	r.ParseForm()
+	if r.Form.Get("direct") != "" {
+		// Directly modify kvstore
+		if keyPos(key) - myPos >= 5 {
+			w.WriteHeader(http.StatusNotFound)
+			return
 		}
-	} else if r.Method == "PUT" {
-		// Read request body
-		b, err := io.ReadAll(r.Body)
+		if r.Method == "GET" {
+			mu.Lock()
+			val, ok := kvstore[key + fmt.Sprint(time.Now().Unix() / 600)]
+			mu.Unlock()
+			if !ok || verify(key, val) != nil {
+				w.WriteHeader(http.StatusNotFound)
+				return
+			}
+			w.Write(val)
+		} else if r.Method == "POST" {
+			val, err := io.ReadAll(r.Body)
+			if err != nil {
+				w.WriteHeader(http.StatusInternalServerError)
+				return
+			}
+			mu.Lock()
+			kvstore[key + fmt.Sprint(time.Now().Unix() / 600)] = val
+			mu.Unlock()
+		}
+		return
+	}
+	if r.Method == "GET" {
+		val, err := dhtGet(key)
+		if err != nil {
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		w.Write([]byte(val))
+	} else if r.Method == "POST" {
+		val, err := io.ReadAll(r.Body)
 		if err != nil {
 			w.WriteHeader(http.StatusInternalServerError)
 			return
 		}
-		// Extract signature
-		valSplit := strings.Split(string(b), "\n")
-		sig := valSplit[len(valSplit)-1]
-		// Verify signature
-		if !ed25519.Verify(pubKey, b[:len(b)-len(sig)-1], []byte(sig)) {
-			w.WriteHeader(http.StatusUnauthorized)
+		err = dhtPut(key, val)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
 			return
 		}
-		if keyPos - myPos < 5 {
-			mu.Lock()
-			kvstore[key] = string(b[:len(b)-len(sig)-1])
-			mu.Unlock()
-		} else {
-
-		}
-	} else {
-		w.WriteHeader(http.StatusMethodNotAllowed)
+		w.WriteHeader(http.StatusOK)
 	}
 }

server/main.go

@@ -12,6 +12,7 @@ import (
 
 type user struct {
 	pubkey []byte
+	servers []string
 }
 
 var mu sync.Mutex
@@ -20,22 +21,7 @@ var myHash string
 var myPos int
 var hashToDomain map[string]string
 var peerHashes []string
-var kvstore map[string]string
-
-// Get the sha256sum of string as a URL-safe unpadded base64 string
-func sha256sum(s string) string {
-	b := sha256.Sum256([]byte(s))
-	return base64.RawURLEncoding.EncodeToString(b[:])
-}
-
-// Decode an ID to a public key
-func asPubKey(s string) ed25519.PublicKey {
-	b, err := base64.RawURLEncoding.DecodeString(s)
-	if err != nil {
-		return nil
-	}
-	return ed25519.PublicKey(b)
-}
+var kvstore map[string][]byte
 
 func main() {
 	bindAddr := flag.String("b", ":4200", "bind address")

server/user.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"crypto/ed25519"
+	"encoding/base64"
+	"errors"
+	"net/http"
+)
+
+func verify(id string, body []byte) error {
+	b, err := base64.RawURLEncoding.DecodeString(id)
+	if err != nil {
+		return err
+	}
+	if len(body) < ed25519.SignatureSize {
+		return errors.New("body too short")
+	}
+	message := body[:len(body)-ed25519.SignatureSize]
+	sig := body[len(body)-ed25519.SignatureSize:]
+	if !ed25519.Verify(ed25519.PublicKey(b), message, sig) {
+		return errors.New("signature verification failed")
+	}
+	return nil
+}
+
+// Create user
+func createHandler(w http.ResponseWriter, r *http.Request) {
+	r.ParseForm()
+	id := r.Form.Get("id")
+	dhtGet(id)
+
+}
+
+// Delete user
+func deleteHandler(w http.ResponseWriter, r *http.Request) {
+
+}