sftpd: auto generate an ed25519 host key too

docs/full-configuration.md

@@ -35,7 +35,7 @@ The `serve` command supports the following flags:
 
 Log file can be rotated on demand sending a `SIGUSR1` signal on Unix based systems and using the command `sftpgo service rotatelogs` on Windows.
 
-If you don't configure any private host key, the daemon will use `id_rsa` and `id_ecdsa` in the configuration directory. If these files don't exist, the daemon will attempt to autogenerate them (if the user that executes SFTPGo has write access to the `config-dir`). The server supports any private key format supported by [`crypto/ssh`](https://github.com/golang/crypto/blob/master/ssh/keys.go#L33).
+If you don't configure any private host key, the daemon will use `id_rsa`, `id_ecdsa` and `id_ed25519` in the configuration directory. If these files don't exist, the daemon will attempt to autogenerate them (if the user that executes SFTPGo has write access to the `config-dir`). The server supports any private key format supported by [`crypto/ssh`](https://github.com/golang/crypto/blob/master/ssh/keys.go#L33).
 
 The `gen` command allows to generate completion scripts for your shell and man pages. Currently the man pages visual representation is wrong, take a look at this upstream [bug](https://github.com/spf13/cobra/issues/1049) for more details.
 
@@ -68,7 +68,7 @@ The configuration file contains the following sections:
   - `actions`, struct. Deprecated, please use the same key in `common` section.
   - `keys`, struct array. Deprecated, please use `host_keys`.
     - `private_key`, path to the private key file. It can be a path relative to the config dir or an absolute one.
-  - `host_keys`, list of strings. It contains the daemon's private host keys. Each host key can be defined as a path relative to the configuration directory or an absolute one. If empty, the daemon will search or try to generate `id_rsa` and `id_ecdsa` keys inside the configuration directory. If you configure absolute paths to files named `id_rsa` and/or `id_ecdsa` then SFTPGo will try to generate these keys using the default settings.
+  - `host_keys`, list of strings. It contains the daemon's private host keys. Each host key can be defined as a path relative to the configuration directory or an absolute one. If empty, the daemon will search or try to generate `id_rsa`, `id_ecdsa` and `id_ed25519` keys inside the configuration directory. If you configure absolute paths to files named `id_rsa`, `id_ecdsa` and/or `id_ed25519` then SFTPGo will try to generate these keys using the default settings.
   - `kex_algorithms`, list of strings. Available KEX (Key Exchange) algorithms in preference order. Leave empty to use default values. The supported values can be found here: [`crypto/ssh`](https://github.com/golang/crypto/blob/master/ssh/common.go#L46 "Supported kex algos")
   - `ciphers`, list of strings. Allowed ciphers. Leave empty to use default values. The supported values can be found here: [crypto/ssh](https://github.com/golang/crypto/blob/master/ssh/common.go#L28 "Supported ciphers")
   - `macs`, list of strings. Available MAC (message authentication code) algorithms in preference order. Leave empty to use default values. The supported values can be found here: [crypto/ssh](https://github.com/golang/crypto/blob/master/ssh/common.go#L84 "Supported MACs")
@@ -172,16 +172,17 @@ If you want to use a private host key that uses an algorithm/setting different f
 
 where `id_rsa`, `id_ecdsa` and `id_ed25519`, in this example, are files containing your generated keys. You can use absolute paths or paths relative to the configuration directory.
 
-If you want the default host keys generation in a directory different from the config dir, please specify absolute paths to files named `id_rsa` or `id_ecdsa` like this:
+If you want the default host keys generation in a directory different from the config dir, please specify absolute paths to files named `id_rsa`, `id_ecdsa` or `id_ed25519` like this:
 
 ```json
 "host_keys": [
   "/etc/sftpgo/keys/id_rsa",
-  "/etc/sftpgo/keys/id_ecdsa"
+  "/etc/sftpgo/keys/id_ecdsa",
+  "/etc/sftpgo/keys/id_ed25519"
 ]
 ```
 
-then SFTPGo will try to create `id_rsa` and `id_ecdsa`, if they are missing, inside the existing directory `/etc/sftpgo/keys`.
+then SFTPGo will try to create `id_rsa`, `id_ecdsa` and `id_ed25519`, if they are missing, inside the existing directory `/etc/sftpgo/keys`.
 
 The configuration can be read from JSON, TOML, YAML, HCL, envfile and Java properties config files. If your `config-file` flag is set to `sftpgo` (default value), you need to create a configuration file called `sftpgo.json` or `sftpgo.yaml` and so on inside `config-dir`.
 

sftpd/internal_test.go

@@ -1741,17 +1741,21 @@ func TestLoadHostKeys(t *testing.T) {
 	assert.NoError(t, err)
 	rsaKeyName := filepath.Join(keysDir, defaultPrivateRSAKeyName)
 	ecdsaKeyName := filepath.Join(keysDir, defaultPrivateECDSAKeyName)
+	ed25519KeyName := filepath.Join(keysDir, defaultPrivateEd25519KeyName)
 	nonDefaultKeyName := filepath.Join(keysDir, "akey")
-	c.HostKeys = []string{nonDefaultKeyName, rsaKeyName, ecdsaKeyName}
+	c.HostKeys = []string{nonDefaultKeyName, rsaKeyName, ecdsaKeyName, ed25519KeyName}
 	err = c.checkAndLoadHostKeys(configDir, serverConfig)
 	assert.Error(t, err)
 	assert.FileExists(t, rsaKeyName)
 	assert.FileExists(t, ecdsaKeyName)
+	assert.FileExists(t, ed25519KeyName)
 	assert.NoFileExists(t, nonDefaultKeyName)
 	err = os.Remove(rsaKeyName)
 	assert.NoError(t, err)
 	err = os.Remove(ecdsaKeyName)
 	assert.NoError(t, err)
+	err = os.Remove(ed25519KeyName)
+	assert.NoError(t, err)
 	if runtime.GOOS != osWindows {
 		err = os.Chmod(keysDir, 0551)
 		assert.NoError(t, err)
@@ -1764,6 +1768,9 @@ func TestLoadHostKeys(t *testing.T) {
 		c.HostKeys = []string{ecdsaKeyName, rsaKeyName}
 		err = c.checkAndLoadHostKeys(configDir, serverConfig)
 		assert.Error(t, err)
+		c.HostKeys = []string{ed25519KeyName}
+		err = c.checkAndLoadHostKeys(configDir, serverConfig)
+		assert.Error(t, err)
 		err = os.Chmod(keysDir, 0755)
 		assert.NoError(t, err)
 	}

sftpd/server.go

@@ -25,9 +25,10 @@ import (
 )
 
 const (
-	defaultPrivateRSAKeyName    = "id_rsa"
-	defaultPrivateECDSAKeyName  = "id_ecdsa"
-	sourceAddressCriticalOption = "source-address"
+	defaultPrivateRSAKeyName     = "id_rsa"
+	defaultPrivateECDSAKeyName   = "id_ecdsa"
+	defaultPrivateEd25519KeyName = "id_ed25519"
+	sourceAddressCriticalOption  = "source-address"
 )
 
 var (
@@ -471,6 +472,33 @@ func (c *Configuration) checkSSHCommands() {
 	c.EnabledSSHCommands = sshCommands
 }
 
+func (c *Configuration) generateDefaultHostKeys(configDir string) error {
+	var err error
+	defaultHostKeys := []string{defaultPrivateRSAKeyName, defaultPrivateECDSAKeyName, defaultPrivateEd25519KeyName}
+	for _, k := range defaultHostKeys {
+		autoFile := filepath.Join(configDir, k)
+		if _, err = os.Stat(autoFile); os.IsNotExist(err) {
+			logger.Info(logSender, "", "No host keys configured and %#v does not exist; try to create a new host key", autoFile)
+			logger.InfoToConsole("No host keys configured and %#v does not exist; try to create a new host key", autoFile)
+			if k == defaultPrivateRSAKeyName {
+				err = utils.GenerateRSAKeys(autoFile)
+			} else if k == defaultPrivateECDSAKeyName {
+				err = utils.GenerateECDSAKeys(autoFile)
+			} else {
+				err = utils.GenerateEd25519Keys(autoFile)
+			}
+			if err != nil {
+				logger.Warn(logSender, "", "error creating host key %#v: %v", autoFile, err)
+				logger.WarnToConsole("error creating host key %#v: %v", autoFile, err)
+				return err
+			}
+		}
+		c.HostKeys = append(c.HostKeys, k)
+	}
+
+	return err
+}
+
 func (c *Configuration) checkHostKeyAutoGeneration(configDir string) error {
 	for _, k := range c.HostKeys {
 		if filepath.IsAbs(k) {
@@ -495,6 +523,15 @@ func (c *Configuration) checkHostKeyAutoGeneration(configDir string) error {
 						logger.WarnToConsole("error creating host key %#v: %v", k, err)
 						return err
 					}
+				case defaultPrivateEd25519KeyName:
+					logger.Info(logSender, "", "try to create non-existent host key %#v", k)
+					logger.InfoToConsole("try to create non-existent host key %#v", k)
+					err = utils.GenerateEd25519Keys(k)
+					if err != nil {
+						logger.Warn(logSender, "", "error creating host key %#v: %v", k, err)
+						logger.WarnToConsole("error creating host key %#v: %v", k, err)
+						return err
+					}
 				default:
 					logger.Warn(logSender, "", "non-existent host key %#v will not be created", k)
 					logger.WarnToConsole("non-existent host key %#v will not be created", k)
@@ -503,24 +540,8 @@ func (c *Configuration) checkHostKeyAutoGeneration(configDir string) error {
 		}
 	}
 	if len(c.HostKeys) == 0 {
-		defaultKeys := []string{defaultPrivateRSAKeyName, defaultPrivateECDSAKeyName}
-		for _, k := range defaultKeys {
-			autoFile := filepath.Join(configDir, k)
-			if _, err := os.Stat(autoFile); os.IsNotExist(err) {
-				logger.Info(logSender, "", "No host keys configured and %#v does not exist; try to create a new host key", autoFile)
-				logger.InfoToConsole("No host keys configured and %#v does not exist; try to create a new host key", autoFile)
-				if k == defaultPrivateRSAKeyName {
-					err = utils.GenerateRSAKeys(autoFile)
-				} else {
-					err = utils.GenerateECDSAKeys(autoFile)
-				}
-				if err != nil {
-					logger.Warn(logSender, "", "error creating host key %#v: %v", autoFile, err)
-					logger.WarnToConsole("error creating host key %#v: %v", autoFile, err)
-					return err
-				}
-			}
-			c.HostKeys = append(c.HostKeys, k)
+		if err := c.generateDefaultHostKeys(configDir); err != nil {
+			return err
 		}
 	}
 	return nil

utils/utils.go

@@ -5,6 +5,7 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/ecdsa"
+	"crypto/ed25519"
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
@@ -230,26 +231,58 @@ func GenerateECDSAKeys(file string) error {
 		return err
 	}
 
+	keyBytes, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return err
+	}
+	priv := &pem.Block{
+		Type:  "EC PRIVATE KEY",
+		Bytes: keyBytes,
+	}
+
 	o, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
 	if err != nil {
 		return err
 	}
 	defer o.Close()
 
-	keyBytes, err := x509.MarshalECPrivateKey(key)
+	if err := pem.Encode(o, priv); err != nil {
+		return err
+	}
+
+	pub, err := ssh.NewPublicKey(&key.PublicKey)
+	if err != nil {
+		return err
+	}
+	return ioutil.WriteFile(file+".pub", ssh.MarshalAuthorizedKey(pub), 0600)
+}
+
+// GenerateEd25519Keys generate ed25519 private and public keys and write the
+// private key to specified file and the public key to the specified
+// file adding the .pub suffix
+func GenerateEd25519Keys(file string) error {
+	pubKey, privKey, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return err
+	}
+	keyBytes, err := x509.MarshalPKCS8PrivateKey(privKey)
 	if err != nil {
 		return err
 	}
 	priv := &pem.Block{
-		Type:  "EC PRIVATE KEY",
+		Type:  "PRIVATE KEY",
 		Bytes: keyBytes,
 	}
+	o, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return err
+	}
+	defer o.Close()
 
 	if err := pem.Encode(o, priv); err != nil {
 		return err
 	}
-
-	pub, err := ssh.NewPublicKey(&key.PublicKey)
+	pub, err := ssh.NewPublicKey(pubKey)
 	if err != nil {
 		return err
 	}