Decrypt settings on start (#2)

src/calanonsync/settings.go

@@ -10,6 +10,7 @@ import (
 	"github.com/spf13/cobra"
 	"golang.org/x/crypto/ssh/terminal"
 	"io"
+	"io/ioutil"
 	"log"
 	"os"
 	"strings"
@@ -33,22 +34,6 @@ type Settings struct {
 const settingsName = "calanonsync.json"
 const keyName = ".calanonsync.key"
 
-func ensurePassword(password *string, name string) {
-	if *password != "" {
-		// Nothing to do. Password already set.
-		return
-	}
-
-	print(name + " password: ")
-	b, err := terminal.ReadPassword(int(syscall.Stdin))
-	println()
-	if err != nil {
-		panic(err)
-	}
-
-	*password = string(b)
-}
-
 func LoadSettings() Settings {
 	f, err := os.Open(settingsName)
 	if err != nil {
@@ -64,6 +49,55 @@ func LoadSettings() Settings {
 		settings.CalDAV.URL += "/"
 	}
 
+	// Load a key if possible.
+	var key []byte = nil
+	keyString, err := ioutil.ReadFile(keyName)
+	if err == nil {
+		key, err = base64.StdEncoding.DecodeString(string(keyString))
+		if err != nil {
+			log.Fatalf("Could not load encryption key: %s\n", err)
+		}
+	} else if !os.IsNotExist(err) {
+		log.Fatalf("Could not load encryption key: %s\n", err)
+	}
+
+	ensurePassword := func(password *string, name string) {
+		if *password == "" {
+			print(name + " password: ")
+			b, err := terminal.ReadPassword(int(syscall.Stdin))
+			println()
+			if err != nil {
+				panic(err)
+			}
+
+			*password = string(b)
+		} else if key != nil {
+			// Password already set. Since we have an encryption key, try to
+			// decrypt the password.
+			pwbytes, err := base64.StdEncoding.DecodeString(*password)
+			if err != nil {
+				log.Fatalf("Could not decode password: %s\n", err)
+			}
+
+			block, err := aes.NewCipher(key)
+			if err != nil {
+				log.Fatalf("Could not create cipher: %s\n", err)
+			}
+
+			if len(pwbytes) < block.BlockSize() {
+				log.Fatalln("Could not decrypt password. Encrypted stream is too short.")
+			}
+
+			iv := pwbytes[:aes.BlockSize]
+			result := pwbytes[aes.BlockSize:]
+
+			stream := cipher.NewCFBDecrypter(block, iv)
+			stream.XORKeyStream(result, result)
+
+			*password = string(result)
+		}
+	}
+
 	ensurePassword(&settings.EWS.Password, "EWS")
 	ensurePassword(&settings.CalDAV.Password, "CalDAV")