truly deterministic RSA keys

mockid/api/common.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"log"
 	"math/rand"
+	mathrand "math/rand"
 	"net/http"
 )
 
@@ -17,11 +18,25 @@ type options struct {
 	KeyType string `json:"kty"`
 	Seed    int64  `json:"-"`
 	SeedStr string `json:"seed"`
-	rndReader io.Reader `json:"-"`
+}
+
+// this shananigans is only for testing and debug API stuff
+func (o *options) nextRand() *mathrand.Rand {
+	if 0 == o.Seed {
+		panic(errors.New("called nextRand impossibly"))
+		return nil
+	}
+	return rand.New(rand.NewSource(o.Seed))
+}
+
+func (o *options) nextReader() io.Reader {
+	if 0 == o.Seed {
+		return RandomReader
+	}
+	return rand.New(rand.NewSource(o.Seed))
 }
 
 func getOpts(r *http.Request) (*options, error) {
-	rndReader := RandomReader
 	tok := make(map[string]interface{})
 	decoder := json.NewDecoder(r.Body)
 	err := decoder.Decode(&tok)
@@ -41,27 +56,25 @@ func getOpts(r *http.Request) (*options, error) {
 		seed, _ = binary.ReadVarint(bytes.NewReader(b[0:8]))
 	}
 
+	opts := &options{
+		Seed: seed,
+	}
+
 	var n int
 	if 0 != seed {
-		rnd := rand.New(rand.NewSource(seed))
-		rndReader = rnd
-		n = rnd.Intn(2)
+		n = opts.nextRand().Intn(2)
 	} else {
 		n = rand.Intn(2)
 	}
 
-	kty, _ := tok["kty"].(string)
-	if "" == kty {
+	opts.KeyType, _ = tok["kty"].(string)
+	if "" == opts.KeyType {
 		if 0 == n {
-			kty = "RSA"
+			opts.KeyType = "RSA"
 		} else {
-			kty = "EC"
+			opts.KeyType = "EC"
 		}
 	}
 
-	return &options{
-		KeyType:   kty,
-		Seed:      seed,
-		rndReader: rndReader,
-	}, nil
+	return opts, nil
 }

mockid/api/generate.go

@@ -38,7 +38,7 @@ func GeneratePrivateJWK(w http.ResponseWriter, r *http.Request) {
 
 // GeneratePrivateDER will create a new private key in a valid DER encoding
 func GeneratePrivateDER(w http.ResponseWriter, r *http.Request) {
-	log.Printf("%s %s\n", r.Method, r.URL.Path)
+	log.Printf("%s %s", r.Method, r.URL.Path)
 	if "POST" != r.Method {
 		http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
 		return
@@ -58,7 +58,7 @@ func GeneratePrivateDER(w http.ResponseWriter, r *http.Request) {
 
 // GeneratePrivatePEM will create a new private key in a valid PEM encoding
 func GeneratePrivatePEM(w http.ResponseWriter, r *http.Request) {
-	log.Printf("%s %s\n", r.Method, r.URL.Path)
+	log.Printf("%s %s", r.Method, r.URL.Path)
 	if "POST" != r.Method {
 		http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
 		return
@@ -80,9 +80,24 @@ func genPrivKey(opts *options) keypairs.PrivateKey {
 	var privkey keypairs.PrivateKey
 	if "RSA" == opts.KeyType {
 		keylen := 2048
-		privkey, _ = rsa.GenerateKey(opts.rndReader, keylen)
+		rndReader := opts.nextReader()
+		privkey, _ = rsa.GenerateKey(rndReader, keylen)
+		if rndReader != RandomReader {
+			for i := 0; i < 16; i++ {
+				otherkey, _ := rsa.GenerateKey(opts.nextRand(), keylen)
+				otherCmp := otherkey.D.Cmp(privkey.(*rsa.PrivateKey).D)
+				if 0 != otherCmp {
+					// There are two possible keys, choose the lesser D value
+					// See https://github.com/square/go-jose/issues/189
+					if otherCmp < 0 {
+						privkey = otherkey
+					}
+					break
+				}
+			}
+		}
 	} else {
-		privkey, _ = ecdsa.GenerateKey(elliptic.P256(), opts.rndReader)
+		privkey, _ = ecdsa.GenerateKey(elliptic.P256(), opts.nextReader())
 	}
 	return privkey
 }

mockid/mockid_test.go

@@ -121,7 +121,7 @@ func TestGenWithSeed(t *testing.T) {
 	res, err := client.Do(&http.Request{
 		Method: "POST",
 		URL:    urlstr,
-		Body:   ioutil.NopCloser(bytes.NewReader([]byte(`{"seed":"c"}`))),
+		Body:   ioutil.NopCloser(bytes.NewReader([]byte(`{"seed":"test"}`))),
 	})
 	if nil != err {
 		//t.Fatal(err)
@@ -135,13 +135,15 @@ func TestGenWithSeed(t *testing.T) {
 		return
 	}
 
+	// See https://github.com/square/go-jose/issues/189
+	for i := 0; i < 8; i++ {
 		// Key B
 		client = srv.Client()
 		urlstr, _ = url.Parse(srv.URL + "/private.jwk.json")
 		res, err = client.Do(&http.Request{
 			Method: "POST",
 			URL:    urlstr,
-		Body:   ioutil.NopCloser(bytes.NewReader([]byte(`{"seed":"c"}`))),
+			Body:   ioutil.NopCloser(bytes.NewReader([]byte(`{"seed":"test"}`))),
 		})
 		if nil != err {
 			//t.Fatal(err)
@@ -156,9 +158,12 @@ func TestGenWithSeed(t *testing.T) {
 		}
 
 		if '{' != dataA[0] || len(dataA) < 100 || string(dataA) != string(dataB) {
+			log.Println(string(dataA))
+			log.Println(string(dataB))
 			t.Error(errors.New("keys with identical seeds should be identical"))
 			return
 		}
+	}
 }
 
 func TestGenWithRand(t *testing.T) {