diff --git a/caddy/https/client.go b/caddy/https/client.go
index 40e7a709..762e58aa 100644
--- a/caddy/https/client.go
+++ b/caddy/https/client.go
@@ -34,16 +34,7 @@ var NewACMEClient = func(email string, allowPrompts bool) (*ACMEClient, error) {
 	}
 
 	// The client facilitates our communication with the CA server.
-	var kt acme.KeyType
-	if rsaKeySizeToUse == Rsa2048 {
-		kt = acme.RSA2048
-	} else if rsaKeySizeToUse == Rsa4096 {
-		kt = acme.RSA4096
-	} else {
-		// TODO(hkjn): Support more types? Current changes are quick fix for #640.
-		return nil, fmt.Errorf("https: unsupported keysize")
-	}
-	client, err := acme.NewClient(CAUrl, &leUser, kt)
+	client, err := acme.NewClient(CAUrl, &leUser, KeyType)
 	if err != nil {
 		return nil, err
 	}
diff --git a/caddy/https/crypto.go b/caddy/https/crypto.go
index efc40d43..bc0ff637 100644
--- a/caddy/https/crypto.go
+++ b/caddy/https/crypto.go
@@ -1,26 +1,52 @@
 package https
 
 import (
+	"crypto"
+	"crypto/ecdsa"
 	"crypto/rsa"
 	"crypto/x509"
 	"encoding/pem"
+	"errors"
 	"io/ioutil"
 	"os"
 )
 
-// loadRSAPrivateKey loads a PEM-encoded RSA private key from file.
-func loadRSAPrivateKey(file string) (*rsa.PrivateKey, error) {
+// loadPrivateKey loads a PEM-encoded ECC/RSA private key from file.
+func loadPrivateKey(file string) (crypto.PrivateKey, error) {
 	keyBytes, err := ioutil.ReadFile(file)
 	if err != nil {
 		return nil, err
 	}
 	keyBlock, _ := pem.Decode(keyBytes)
-	return x509.ParsePKCS1PrivateKey(keyBlock.Bytes)
+	
+	switch keyBlock.Type {
+	case "RSA PRIVATE KEY":
+		return x509.ParsePKCS1PrivateKey(keyBlock.Bytes)
+	case "EC PRIVATE KEY":
+		return x509.ParseECPrivateKey(keyBlock.Bytes)
+	}
+
+	return nil, errors.New("unknown private key type")
 }
 
-// saveRSAPrivateKey saves a PEM-encoded RSA private key to file.
-func saveRSAPrivateKey(key *rsa.PrivateKey, file string) error {
-	pemKey := pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)}
+// savePrivateKey saves a PEM-encoded ECC/RSA private key to file.
+func savePrivateKey(key crypto.PrivateKey, file string) error {
+	var pemType string
+	var keyBytes []byte
+	switch key := key.(type) {
+	case *ecdsa.PrivateKey:
+		var err error
+		pemType = "EC"
+		keyBytes, err = x509.MarshalECPrivateKey(key)
+		if err != nil {
+			return err
+		}
+	case *rsa.PrivateKey:
+		pemType = "RSA"
+		keyBytes = x509.MarshalPKCS1PrivateKey(key)
+	}
+	
+	pemKey := pem.Block{Type: pemType + " PRIVATE KEY", Bytes: keyBytes}
 	keyOut, err := os.Create(file)
 	if err != nil {
 		return err
diff --git a/caddy/https/crypto_test.go b/caddy/https/crypto_test.go
index 39cd27b5..c1f32b27 100644
--- a/caddy/https/crypto_test.go
+++ b/caddy/https/crypto_test.go
@@ -2,6 +2,9 @@ package https
 
 import (
 	"bytes"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/x509"
@@ -10,23 +13,17 @@ import (
 	"testing"
 )
 
-func init() {
-	rsaKeySizeToUse = 2048 // TODO(hkjn): Bring back support for small
-	// keys to speed up tests? Current changes
-	// are quick fix for #640.
-}
-
 func TestSaveAndLoadRSAPrivateKey(t *testing.T) {
 	keyFile := "test.key"
 	defer os.Remove(keyFile)
 
-	privateKey, err := rsa.GenerateKey(rand.Reader, rsaKeySizeToUse)
+	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
 	if err != nil {
 		t.Fatal(err)
 	}
 
 	// test save
-	err = saveRSAPrivateKey(privateKey, keyFile)
+	err = savePrivateKey(privateKey, keyFile)
 	if err != nil {
 		t.Fatal("error saving private key:", err)
 	}
@@ -45,23 +42,70 @@ func TestSaveAndLoadRSAPrivateKey(t *testing.T) {
 	}
 
 	// test load
-	loadedKey, err := loadRSAPrivateKey(keyFile)
+	loadedKey, err := loadPrivateKey(keyFile)
 	if err != nil {
 		t.Error("error loading private key:", err)
 	}
 
 	// verify loaded key is correct
-	if !rsaPrivateKeysSame(privateKey, loadedKey) {
+	if !PrivateKeysSame(privateKey, loadedKey) {
 		t.Error("Expected key bytes to be the same, but they weren't")
 	}
 }
 
-// rsaPrivateKeysSame compares the bytes of a and b and returns true if they are the same.
-func rsaPrivateKeysSame(a, b *rsa.PrivateKey) bool {
-	return bytes.Equal(rsaPrivateKeyBytes(a), rsaPrivateKeyBytes(b))
+func TestSaveAndLoadECCPrivateKey(t *testing.T) {
+	keyFile := "test.key"
+	defer os.Remove(keyFile)
+
+	privateKey, err := ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// test save
+	err = savePrivateKey(privateKey, keyFile)
+	if err != nil {
+		t.Fatal("error saving private key:", err)
+	}
+
+	// it doesn't make sense to test file permission on windows
+	if runtime.GOOS != "windows" {
+		// get info of the key file
+		info, err := os.Stat(keyFile)
+		if err != nil {
+			t.Fatal("error stating private key:", err)
+		}
+		// verify permission of key file is correct
+		if info.Mode().Perm() != 0600 {
+			t.Error("Expected key file to have permission 0600, but it wasn't")
+		}
+	}
+
+	// test load
+	loadedKey, err := loadPrivateKey(keyFile)
+	if err != nil {
+		t.Error("error loading private key:", err)
+	}
+
+	// verify loaded key is correct
+        if !PrivateKeysSame(privateKey, loadedKey) {
+                t.Error("Expected key bytes to be the same, but they weren't")
+        }
 }
 
-// rsaPrivateKeyBytes returns the bytes of DER-encoded key.
-func rsaPrivateKeyBytes(key *rsa.PrivateKey) []byte {
-	return x509.MarshalPKCS1PrivateKey(key)
+// PrivateKeysSame compares the bytes of a and b and returns true if they are the same.
+func PrivateKeysSame(a, b crypto.PrivateKey) bool {
+	return bytes.Equal(PrivateKeyBytes(a), PrivateKeyBytes(b))
+}
+
+// PrivateKeyBytes returns the bytes of DER-encoded key.
+func PrivateKeyBytes(key crypto.PrivateKey) []byte {
+	var keyBytes []byte
+	switch key := key.(type) {
+	case *rsa.PrivateKey:
+		keyBytes = x509.MarshalPKCS1PrivateKey(key)
+	case *ecdsa.PrivateKey:
+		keyBytes, _ = x509.MarshalECPrivateKey(key)
+	}
+	return keyBytes
 }
diff --git a/caddy/https/https.go b/caddy/https/https.go
index 90022ed5..76e5e312 100644
--- a/caddy/https/https.go
+++ b/caddy/https/https.go
@@ -401,21 +401,10 @@ var (
 // default port for the challenge must be forwarded to this one.
 const AlternatePort = "5033"
 
-// KeySize represents the length of a key in bits.
-type KeySize int
-
-// Key sizes are used to determine the strength of a key.
-const (
-	Ecc224  KeySize = 224
-	Ecc256          = 256
-	Rsa2048         = 2048
-	Rsa4096         = 4096
-)
-
-// rsaKeySizeToUse is the size to use for new RSA keys.
+// KeyType is the type to use for new keys.
 // This shouldn't need to change except for in tests;
 // the size can be drastically reduced for speed.
-var rsaKeySizeToUse = Rsa2048
+var KeyType = acme.EC384
 
 // stopChan is used to signal the maintenance goroutine
 // to terminate.
diff --git a/caddy/https/user.go b/caddy/https/user.go
index 203e07a2..a7e6e5f6 100644
--- a/caddy/https/user.go
+++ b/caddy/https/user.go
@@ -3,8 +3,9 @@ package https
 import (
 	"bufio"
 	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
 	"crypto/rand"
-	"crypto/rsa"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -21,7 +22,7 @@ import (
 type User struct {
 	Email        string
 	Registration *acme.RegistrationResource
-	key          *rsa.PrivateKey
+	key          crypto.PrivateKey
 }
 
 // GetEmail gets u's email.
@@ -64,7 +65,7 @@ func getUser(email string) (User, error) {
 	}
 
 	// load their private key
-	user.key, err = loadRSAPrivateKey(storage.UserKeyFile(email))
+	user.key, err = loadPrivateKey(storage.UserKeyFile(email))
 	if err != nil {
 		return user, err
 	}
@@ -83,7 +84,7 @@ func saveUser(user User) error {
 	}
 
 	// save private key file
-	err = saveRSAPrivateKey(user.key, storage.UserKeyFile(user.Email))
+	err = savePrivateKey(user.key, storage.UserKeyFile(user.Email))
 	if err != nil {
 		return err
 	}
@@ -104,7 +105,7 @@ func saveUser(user User) error {
 // instead. It does NOT prompt the user.
 func newUser(email string) (User, error) {
 	user := User{Email: email}
-	privateKey, err := rsa.GenerateKey(rand.Reader, rsaKeySizeToUse)
+	privateKey, err := ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
 	if err != nil {
 		return user, errors.New("error generating private key: " + err.Error())
 	}
diff --git a/caddy/https/user_test.go b/caddy/https/user_test.go
index 5bc28b04..c1d115e1 100644
--- a/caddy/https/user_test.go
+++ b/caddy/https/user_test.go
@@ -114,7 +114,7 @@ func TestGetUserAlreadyExists(t *testing.T) {
 	}
 
 	// Assert keys are the same
-	if !rsaPrivateKeysSame(user.key, user2.key) {
+	if !PrivateKeysSame(user.key, user2.key) {
 		t.Error("Expected private key to be the same after loading, but it wasn't")
 	}