diff --git a/global/deviceIDs.go b/global/deviceIDs.go
index c4f32cf..2737365 100644
--- a/global/deviceIDs.go
+++ b/global/deviceIDs.go
@@ -7,19 +7,19 @@ import (
 )
 
 // GetCurrentDeviceID returns the current device ID or
-// FSMisc if there is no device ID (e.g. first run).
-func GetCurrentDeviceID() (string, error) {
+// nil if there is no device ID (e.g. first run).
+func GetCurrentDeviceID() (*string, error) {
 	deviceIDList, err := GenDeviceIDList()
 	if err != nil {
-		return "", errors.New("unable to generate device ID list: " + err.Error())
+		return nil, errors.New("unable to generate device ID list: " + err.Error())
 	}
 	var deviceID string
 	if len(deviceIDList) > 0 {
 		deviceID = (deviceIDList)[0].Name()
 	} else {
-		deviceID = FSMisc // indicates to server that no device ID is being replaced
+		return nil, nil // nil device ID indicates to server that no device ID is being replaced
 	}
-	return deviceID, nil
+	return &deviceID, nil
 }
 
 // GenDeviceIDList returns a slice of all registered device IDs.
diff --git a/global/init.go b/global/init.go
index 82f0fcf..47d5dcf 100644
--- a/global/init.go
+++ b/global/init.go
@@ -9,36 +9,35 @@ import (
 
 // DirInit creates the libmutton directories.
 // Returns: oldDeviceID (from before the directory reset; will be FSMisc if there is no pre-existing ID).
-func DirInit(preserveOldCfgDir bool) (string, error) {
+func DirInit(preserveOldCfgDir bool) (*string, error) {
+	var err error
+
 	// create EntryRoot
-	if err := os.MkdirAll(EntryRoot, 0700); err != nil {
-		return "", errors.New("unable to create \"" + EntryRoot + "\": " + err.Error())
+	if err = os.MkdirAll(EntryRoot, 0700); err != nil {
+		return nil, errors.New("unable to create \"" + EntryRoot + "\": " + err.Error())
 	}
 
 	// get old device ID before its potential removal
-	oldDeviceID, err := GetCurrentDeviceID()
-	if err != nil {
-		oldDeviceID = FSMisc
-	}
+	oldDeviceID, _ := GetCurrentDeviceID() // error ignored; oldDeviceID is set to nil on error, which is the correct assumption
 
 	// remove existing config directory (if it exists and not in append mode)
 	if !preserveOldCfgDir {
 		isAccessible, _ := back.TargetIsFile(CfgDir, false) // error is ignored because dir/file status is irrelevant
 		if isAccessible {
 			if err = os.RemoveAll(CfgDir); err != nil {
-				return "", errors.New("unable to remove existing config directory: " + err.Error())
+				return nil, errors.New("unable to remove existing config directory: " + err.Error())
 			}
 		}
 	}
 
 	// create config directory w/devices subdirectory
 	if err = os.MkdirAll(CfgDir+PathSeparator+"devices", 0700); err != nil {
-		return "", errors.New("unable to create \"" + CfgDir + "\": " + err.Error())
+		return nil, errors.New("unable to create \"" + CfgDir + "\": " + err.Error())
 	}
 
 	// create password age directory
 	if err = os.MkdirAll(AgeDir, 0700); err != nil {
-		return "", errors.New("unable to create \"" + AgeDir + "\": " + err.Error())
+		return nil, errors.New("unable to create \"" + AgeDir + "\": " + err.Error())
 	}
 
 	return oldDeviceID, nil
diff --git a/libmuttonserver.go b/libmuttonserver.go
index 9566bc2..06dcb92 100644
--- a/libmuttonserver.go
+++ b/libmuttonserver.go
@@ -93,17 +93,22 @@ func main() {
 		}
 	case "register":
 		// register a new device ID
-		// stdin[0] is expected to be the device ID
-		// stdin[1] is expected to be the old device ID (for removal)
-		f, err := os.OpenFile(global.CfgDir+global.PathSeparator+"devices"+global.PathSeparator+stdin[0], os.O_CREATE|os.O_WRONLY, 0600)
+		// stdin[0] is expected to be JSON matching type synccommon.RegisterReqT
+		var registerReq synccommon.RegisterReqT
+		err := json.Unmarshal([]byte(stdin[0]), &registerReq)
+		if err != nil {
+			fmt.Printf("{\"errMsg\":\"%s\"}", err.Error())
+			return
+		}
+		f, err := os.OpenFile(global.CfgDir+global.PathSeparator+"devices"+global.PathSeparator+registerReq.NewDeviceID, os.O_CREATE|os.O_WRONLY, 0600)
 		if err != nil {
 			fmt.Printf("{\"errMsg\":\"%s\"}", err.Error())
 			return
 		}
 		_ = f.Close()
-		if stdin[1] != global.FSMisc { // FSMisc is used to indicate that no device ID is being replaced
+		if registerReq.OldDeviceID != nil { // nil is used to indicate that no device ID is being replaced
 			// remove the old device ID file
-			if err = os.RemoveAll(global.CfgDir + global.PathSeparator + "devices" + global.PathSeparator + stdin[1]); err != nil {
+			if err = os.RemoveAll(global.CfgDir + global.PathSeparator + "devices" + global.PathSeparator + *registerReq.OldDeviceID); err != nil {
 				fmt.Printf("{\"errMsg\":\"%s\"}", err.Error())
 				return
 			}
@@ -116,8 +121,8 @@ func main() {
 			}
 			for _, deletion := range deletionsList {
 				affectedIDVanityPath := strings.Split(deletion.Name(), global.FSSpace)
-				if affectedIDVanityPath[0] == stdin[1] {
-					if err = os.Rename(deletionsDirRoot+deletion.Name(), deletionsDirRoot+stdin[0]+global.FSSpace+affectedIDVanityPath[1]+global.FSSpace+affectedIDVanityPath[2]); err != nil {
+				if affectedIDVanityPath[0] == *registerReq.OldDeviceID {
+					if err = os.Rename(deletionsDirRoot+deletion.Name(), deletionsDirRoot+registerReq.NewDeviceID+global.FSSpace+affectedIDVanityPath[1]+global.FSSpace+affectedIDVanityPath[2]); err != nil {
 						fmt.Printf("{\"errMsg\":\"%s\"}", err.Error())
 						return
 					}
@@ -126,8 +131,7 @@ func main() {
 		}
 
 		// print EntryRoot, AgeDir and bool indicating OS type to stdout for client to store in config
-		registerResp := synccommon.RegisterRespT{EntryRoot: global.EntryRoot, AgeDir: global.AgeDir, IsWindows: global.IsWindows}
-		registerRespBytes, err := json.Marshal(registerResp)
+		registerRespBytes, err := json.Marshal(synccommon.RegisterRespT{EntryRoot: global.EntryRoot, AgeDir: global.AgeDir, IsWindows: global.IsWindows})
 		if err != nil {
 			fmt.Printf("{\"errMsg\":\"%s\"}", err.Error())
 			return
diff --git a/syncclient/oneOff.go b/syncclient/oneOff.go
index 537a3d7..21f00d9 100644
--- a/syncclient/oneOff.go
+++ b/syncclient/oneOff.go
@@ -164,7 +164,7 @@ end:
 // Device IDs are guaranteed unique as the current UNIX time is appended to them.
 // Leave prefix empty to use the current hostname as the prefix.
 // Returns: the remote EntryRoot, the remote AgeDir, and OS type indicator.
-func GenDeviceID(oldDeviceID, prefix string) (string, string, bool, error) {
+func GenDeviceID(oldDeviceID *string, prefix string) (string, string, bool, error) {
 	// generate new device ID
 	if prefix == "" {
 		prefix, _ = os.Hostname()
@@ -173,7 +173,10 @@ func GenDeviceID(oldDeviceID, prefix string) (string, string, bool, error) {
 
 	// create new device ID file (locally)
 	newDeviceIDPath := global.CfgDir + global.PathSeparator + "devices" + global.PathSeparator + newDeviceID
-	oldDeviceIDPath := global.CfgDir + global.PathSeparator + "devices" + global.PathSeparator + oldDeviceID
+	var oldDeviceIDPath string
+	if oldDeviceID != nil {
+		oldDeviceIDPath = global.CfgDir + global.PathSeparator + "devices" + global.PathSeparator + *oldDeviceID
+	}
 	f, err := os.OpenFile(newDeviceIDPath, os.O_CREATE|os.O_WRONLY, 0600)
 	if err != nil {
 		return "", "", false, errors.New("unable to create local device ID file: " + err.Error())
@@ -183,7 +186,7 @@ func GenDeviceID(oldDeviceID, prefix string) (string, string, bool, error) {
 	cleanupOnFail := func() {
 		// remove new device ID file
 		_ = os.RemoveAll(newDeviceIDPath)
-		if oldDeviceID != global.FSMisc {
+		if oldDeviceID != nil {
 			// restore old device ID file (if it existed and has already been removed due to DirInit)
 			if isAccessible, _ := back.TargetIsFile(oldDeviceIDPath, true); !isAccessible {
 				f, _ := os.OpenFile(oldDeviceIDPath, os.O_CREATE|os.O_WRONLY, 0600)
@@ -200,7 +203,11 @@ func GenDeviceID(oldDeviceID, prefix string) (string, string, bool, error) {
 		cleanupOnFail()
 		return "", "", false, errors.New("unable to connect to SSH client: " + err.Error())
 	}
-	output, err := GetSSHOutput(sshClient, "libmuttonserver register", newDeviceID+"\n"+oldDeviceID)
+	registerReqBytes, err := json.Marshal(synccommon.RegisterReqT{NewDeviceID: newDeviceID, OldDeviceID: oldDeviceID})
+	if err != nil {
+		return "", "", false, errors.New("unable to marshal client register request: " + err.Error())
+	}
+	output, err := GetSSHOutput(sshClient, "libmuttonserver register", string(registerReqBytes))
 	if err != nil {
 		cleanupOnFail()
 		return "", "", false, errors.New("unable to register device ID with server: " + err.Error())
@@ -217,9 +224,11 @@ func GenDeviceID(oldDeviceID, prefix string) (string, string, bool, error) {
 	_ = sshClient.Close() // ignore error; non-critical/unlikely/not much could be done about it
 
 	// remove old device ID file (locally; may not exist)
-	if err = os.RemoveAll(oldDeviceIDPath); err != nil {
-		cleanupOnFail()
-		return "", "", false, errors.New("unable to remove old device ID file (locally): " + err.Error())
+	if oldDeviceID != nil {
+		if err = os.RemoveAll(oldDeviceIDPath); err != nil {
+			cleanupOnFail()
+			return "", "", false, errors.New("unable to remove old device ID file (locally): " + err.Error())
+		}
 	}
 
 	return registerResp.EntryRoot, registerResp.AgeDir, registerResp.IsWindows, nil
diff --git a/synccommon/common.go b/synccommon/common.go
index 95583af..3bf9794 100644
--- a/synccommon/common.go
+++ b/synccommon/common.go
@@ -42,6 +42,11 @@ type RegisterRespT struct {
 	IsWindows bool    `json:"isWindows"`
 }
 
+type RegisterReqT struct {
+	NewDeviceID string  `json:"newDeviceID"`
+	OldDeviceID *string `json:"oldDeviceID"` // nil if not replacing an existing device ID
+}
+
 // GetAllEntryData returns a map of all vanity paths to
 // their respective containing folders and mod+age timestamps.
 func GetAllEntryData() (EntryMapT, error) {