auto generate additional ssh keys

cmd/generate.go

@@ -5,13 +5,17 @@
 package cmd
 
 import (
+	"bufio"
+	"encoding/pem"
 	"fmt"
 	"os"
+	"strings"
 
 	"code.gitea.io/gitea/modules/generate"
 
 	"github.com/mattn/go-isatty"
 	"github.com/urfave/cli/v2"
+	"golang.org/x/crypto/ssh"
 )
 
 var (
@@ -21,6 +25,7 @@ var (
 		Usage: "Generate Gitea's secrets/keys/tokens",
 		Subcommands: []*cli.Command{
 			subcmdSecret,
+			subcmdKeygen,
 		},
 	}
 
@@ -33,6 +38,17 @@ var (
 			microcmdGenerateSecretKey,
 		},
 	}
+	keygenFlags = []cli.Flag{
+		&cli.StringFlag{Name: "bits", Aliases: []string{"b"}, Usage: "Number of bits in the key, ignored when key is ed25519"},
+		&cli.StringFlag{Name: "type", Aliases: []string{"t"}, Value: "ed25519", Usage: "Keytype to generate"},
+		&cli.StringFlag{Name: "file", Aliases: []string{"f"}, Usage: "Specifies the filename of the key file", Required: true},
+	}
+	subcmdKeygen = &cli.Command{
+		Name:   "ssh-keygen",
+		Usage:  "Generate a ssh keypair",
+		Flags:  keygenFlags,
+		Action: runGenerateKeyPair,
+	}
 
 	microcmdGenerateInternalToken = &cli.Command{
 		Name:   "INTERNAL_TOKEN",
@@ -98,3 +114,49 @@ func runGenerateSecretKey(c *cli.Context) error {
 
 	return nil
 }
+
+func runGenerateKeyPair(c *cli.Context) error {
+	file := c.String("file")
+
+	// Check if file exists to prevent overwrites
+	if _, err := os.Stat(file); err == nil {
+		scanner := bufio.NewScanner(os.Stdin)
+		fmt.Printf("%s already exists.\nOverwrite (y/n)? ", file)
+		scanner.Scan()
+		if strings.ToLower(strings.TrimSpace(scanner.Text())) != "y" {
+			fmt.Println("Aborting")
+			return nil
+		}
+	}
+	keytype := c.String("type")
+	bits := c.Int("bits")
+	// provide defaults for bits, ed25519 ignores bit length so it's omitted
+	if bits == 0 {
+		if keytype == "rsa" {
+			bits = 3072
+		} else {
+			bits = 256
+		}
+	}
+
+	pub, priv, err := generate.NewSSHKey(keytype, bits)
+	if err != nil {
+		return err
+	}
+	f, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o600)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	err = pem.Encode(f, priv)
+	if err != nil {
+		return err
+	}
+	fmt.Printf("Your identification has been saved in %s\n", file)
+	err = os.WriteFile(file+".pub", ssh.MarshalAuthorizedKey(pub), 0o644)
+	if err != nil {
+		return err
+	}
+	fmt.Printf("Your public key has been saved in %s", file+".pub")
+	return nil
+}

modules/generate/generate.go

@@ -5,15 +5,22 @@
 package generate
 
 import (
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
 	"crypto/rand"
+	"crypto/rsa"
 	"encoding/base64"
+	"encoding/pem"
 	"fmt"
 	"io"
 	"time"
 
 	"code.gitea.io/gitea/modules/util"
 
 	"github.com/golang-jwt/jwt/v5"
+	"golang.org/x/crypto/ssh"
 )
 
 // NewInternalToken generate a new value intended to be used by INTERNAL_TOKEN.
@@ -72,3 +79,59 @@ func NewSecretKey() (string, error) {
 
 	return secretKey, nil
 }
+
+func NewSSHKey(keytype string, bits int) (ssh.PublicKey, *pem.Block, error) {
+	pub, priv, err := commonKeyGen(keytype, bits)
+	if err != nil {
+		return nil, nil, err
+	}
+	pemPriv, err := ssh.MarshalPrivateKey(priv, "")
+	if err != nil {
+		return nil, nil, err
+	}
+	sshPub, err := ssh.NewPublicKey(pub)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return sshPub, pemPriv, nil
+}
+
+// commonKeyGen is an abstraction over rsa, ecdsa and ed25519 generating functions
+func commonKeyGen(keytype string, bits int) (publicKey, privateKey crypto.PublicKey, err error) {
+	switch keytype {
+	case "rsa":
+		privateKey, err := rsa.GenerateKey(rand.Reader, bits)
+		if err != nil {
+			return nil, nil, err
+		}
+		return &privateKey.PublicKey, privateKey, nil
+	case "ed25519":
+		return ed25519.GenerateKey(rand.Reader)
+	case "ecdsa":
+		curve, err := getElipticCurve(bits)
+		if err != nil {
+			return nil, nil, err
+		}
+		privateKey, err := ecdsa.GenerateKey(curve, rand.Reader)
+		if err != nil {
+			return nil, nil, err
+		}
+		return &privateKey.PublicKey, privateKey, nil
+	default:
+		return nil, nil, fmt.Errorf("unknown keytype: %s", keytype)
+	}
+}
+
+func getElipticCurve(bits int) (elliptic.Curve, error) {
+	switch bits {
+	case 256:
+		return elliptic.P256(), nil
+	case 384:
+		return elliptic.P384(), nil
+	case 521:
+		return elliptic.P521(), nil
+	default:
+		return nil, fmt.Errorf("unsupported ECDSA curve bit length: %d", bits)
+	}
+}

modules/setting/ssh.go

@@ -56,7 +56,7 @@ var SSH = struct {
 	ServerMACs:                    []string{"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1"},
 	MinimumKeySizeCheck:           true,
 	MinimumKeySizes:               map[string]int{"ed25519": 256, "ed25519-sk": 256, "ecdsa": 256, "ecdsa-sk": 256, "rsa": 3071},
-	ServerHostKeys:                []string{"ssh/gitea.rsa", "ssh/gogs.rsa"},
+	ServerHostKeys:                []string{"ssh/gitea.rsa", "ssh/gitea.ed25519", "ssh/gitea.ecdsa", "ssh/gogs.rsa"},
 	AuthorizedKeysCommandTemplate: "{{.AppPath}} --config={{.CustomConf}} serv key-{{.Key.ID}}",
 	PerWriteTimeout:               PerWriteTimeout,
 	PerWritePerKbTimeout:          PerWritePerKbTimeout,

modules/ssh/ssh.go

@@ -6,9 +6,6 @@ package ssh
 import (
 	"bytes"
 	"context"
-	"crypto/rand"
-	"crypto/rsa"
-	"crypto/x509"
 	"encoding/pem"
 	"errors"
 	"io"
@@ -23,6 +20,7 @@ import (
 	"syscall"
 
 	asymkey_model "code.gitea.io/gitea/models/asymkey"
+	"code.gitea.io/gitea/modules/generate"
 	"code.gitea.io/gitea/modules/graceful"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/process"
@@ -54,6 +52,14 @@ import (
 
 const giteaPermissionExtensionKeyID = "gitea-perm-ext-key-id"
 
+type KeyType string
+
+const (
+	RSA     KeyType = "rsa"
+	ECDSA   KeyType = "ecdsa"
+	ED25519 KeyType = "ed25519"
+)
+
 func getExitStatusFromError(err error) int {
 	if err == nil {
 		return 0
@@ -367,17 +373,17 @@ func Listen(host string, port int, ciphers, keyExchanges, macs []string) {
 
 	if len(keys) == 0 {
 		filePath := filepath.Dir(setting.SSH.ServerHostKeys[0])
-
 		if err := os.MkdirAll(filePath, os.ModePerm); err != nil {
 			log.Error("Failed to create dir %s: %v", filePath, err)
 		}
-
-		err := GenKeyPair(setting.SSH.ServerHostKeys[0])
+		err := initDefaultKeys(filePath)
 		if err != nil {
 			log.Fatal("Failed to generate private key: %v", err)
 		}
-		log.Trace("New private key is generated: %s", setting.SSH.ServerHostKeys[0])
-		keys = append(keys, setting.SSH.ServerHostKeys[0])
+		for _, keytype := range []string{"rsa", "ecdsa", "ed25519"} {
+			filename := filePath + "/gitea." + keytype
+			keys = append(keys, filename)
+		}
 	}
 
 	for _, key := range keys {
@@ -387,7 +393,6 @@ func Listen(host string, port int, ciphers, keyExchanges, macs []string) {
 			log.Error("Failed to set Host Key. %s", err)
 		}
 	}
-
 	go func() {
 		_, _, finished := process.GetManager().AddTypedContext(graceful.GetManager().HammerContext(), "Service: Built-in SSH server", process.SystemProcessType, true)
 		defer finished()
@@ -398,13 +403,17 @@ func Listen(host string, port int, ciphers, keyExchanges, macs []string) {
 // GenKeyPair make a pair of public and private keys for SSH access.
 // Public key is encoded in the format for inclusion in an OpenSSH authorized_keys file.
 // Private Key generated is PEM encoded
-func GenKeyPair(keyPath string) error {
-	privateKey, err := rsa.GenerateKey(rand.Reader, 4096)
+func GenKeyPair(keyPath, keytype string) error {
+	bits := 4096
+	if keytype == "ecdsa" {
+		bits = 256
+	}
+
+	publicKey, privateKeyPEM, err := generate.NewSSHKey(keytype, bits)
 	if err != nil {
 		return err
 	}
 
-	privateKeyPEM := &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)}
 	f, err := os.OpenFile(keyPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o600)
 	if err != nil {
 		return err
@@ -419,13 +428,7 @@ func GenKeyPair(keyPath string) error {
 		return err
 	}
 
-	// generate public key
-	pub, err := gossh.NewPublicKey(&privateKey.PublicKey)
-	if err != nil {
-		return err
-	}
-
-	public := gossh.MarshalAuthorizedKey(pub)
+	public := gossh.MarshalAuthorizedKey(publicKey)
 	p, err := os.OpenFile(keyPath+".pub", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o600)
 	if err != nil {
 		return err
@@ -438,3 +441,19 @@ func GenKeyPair(keyPath string) error {
 	_, err = p.Write(public)
 	return err
 }
+
+// initDefaultKeys mirrors how ssh-keygen -A operates
+// it runs checks if public and private keys are already defined and creates new ones if not present
+// key naming does not follow the openssh convention due to existing settings being gitea.{keytype} so generation follows gitea convention
+func initDefaultKeys(path string) error {
+	var errs []error
+	keytypes := []string{"rsa", "ecdsa", "ed25519"}
+	for _, keytype := range keytypes {
+		privExists, _ := util.IsExist(path + "/gitea." + keytype)
+		pubExists, _ := util.IsExist(path + "/gitea." + keytype + ".pub")
+		if !privExists || !pubExists {
+			errs = append(errs, GenKeyPair(path+"/gitea."+keytype, keytype))
+		}
+	}
+	return errors.Join(errs...)
+}