task 256: support passphrase-protected key loading

2 files changed, 128 insertions, 1 deletions

diff --git a/internal/ssh/ssh.go b/internal/ssh/ssh.go
index a191fd5..25b9d28 100644
--- a/internal/ssh/ssh.go
+++ b/internal/ssh/ssh.go
@@ -6,6 +6,7 @@ import (
 	"crypto/rsa"
 	"crypto/x509"
 	"encoding/pem"
+	"errors"
 	"fmt"
 	"net"
 	"os"
@@ -121,7 +122,20 @@ func PrivateKeySigner(keyFile string) (gossh.Signer, error) {
 	}
 	key, err := gossh.ParsePrivateKey(buffer)
 	if err != nil {
-		return nil, err
+		var passphraseMissingErr *gossh.PassphraseMissingError
+		if !errors.As(err, &passphraseMissingErr) {
+			return nil, err
+		}
+
+		passphrase := os.Getenv("DTAIL_KEY_PASSPHRASE")
+		if passphrase == "" {
+			return nil, err
+		}
+
+		key, err = gossh.ParsePrivateKeyWithPassphrase(buffer, []byte(passphrase))
+		if err != nil {
+			return nil, err
+		}
 	}
 	return key, nil
 }
diff --git a/internal/ssh/ssh_test.go b/internal/ssh/ssh_test.go
new file mode 100644
index 0000000..f413145
--- /dev/null
+++ b/internal/ssh/ssh_test.go
@@ -0,0 +1,113 @@
+package ssh
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/pem"
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+
+	gossh "golang.org/x/crypto/ssh"
+)
+
+func TestPrivateKeySignerLoadsUnencryptedKey(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	if err := os.WriteFile(keyFile, EncodePrivateKeyToPEM(privateKey), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	signer, err := PrivateKeySigner(keyFile)
+	if err != nil {
+		t.Fatalf("PrivateKeySigner failed: %v", err)
+	}
+	if signer == nil {
+		t.Fatalf("PrivateKeySigner returned nil signer")
+	}
+}
+
+func TestPrivateKeySignerLoadsEncryptedKeyWithEnvPassphrase(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	block, err := gossh.MarshalPrivateKeyWithPassphrase(privateKey, "", []byte("secret-passphrase"))
+	if err != nil {
+		t.Fatalf("MarshalPrivateKeyWithPassphrase failed: %v", err)
+	}
+	if err := os.WriteFile(keyFile, pem.EncodeToMemory(block), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	t.Setenv("DTAIL_KEY_PASSPHRASE", "secret-passphrase")
+
+	signer, err := PrivateKeySigner(keyFile)
+	if err != nil {
+		t.Fatalf("PrivateKeySigner failed: %v", err)
+	}
+	if signer == nil {
+		t.Fatalf("PrivateKeySigner returned nil signer")
+	}
+}
+
+func TestPrivateKeySignerReturnsPassphraseMissingWithoutEnv(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	block, err := gossh.MarshalPrivateKeyWithPassphrase(privateKey, "", []byte("secret-passphrase"))
+	if err != nil {
+		t.Fatalf("MarshalPrivateKeyWithPassphrase failed: %v", err)
+	}
+	if err := os.WriteFile(keyFile, pem.EncodeToMemory(block), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	_, err = PrivateKeySigner(keyFile)
+	if err == nil {
+		t.Fatalf("PrivateKeySigner succeeded without passphrase env")
+	}
+
+	var passphraseMissingErr *gossh.PassphraseMissingError
+	if !errors.As(err, &passphraseMissingErr) {
+		t.Fatalf("PrivateKeySigner returned %T, want PassphraseMissingError", err)
+	}
+}
+
+func TestPrivateKeySignerRejectsIncorrectEnvPassphrase(t *testing.T) {
+	keyFile := filepath.Join(t.TempDir(), "id_rsa")
+	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
+	if err != nil {
+		t.Fatalf("GenerateKey failed: %v", err)
+	}
+
+	block, err := gossh.MarshalPrivateKeyWithPassphrase(privateKey, "", []byte("secret-passphrase"))
+	if err != nil {
+		t.Fatalf("MarshalPrivateKeyWithPassphrase failed: %v", err)
+	}
+	if err := os.WriteFile(keyFile, pem.EncodeToMemory(block), 0o600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	t.Setenv("DTAIL_KEY_PASSPHRASE", "wrong-passphrase")
+
+	_, err = PrivateKeySigner(keyFile)
+	if err == nil {
+		t.Fatalf("PrivateKeySigner succeeded with wrong passphrase env")
+	}
+
+	var passphraseMissingErr *gossh.PassphraseMissingError
+	if errors.As(err, &passphraseMissingErr) {
+		t.Fatalf("PrivateKeySigner returned PassphraseMissingError instead of parse failure")
+	}
+}