From 66da93301d7e6b3cc5d5301600df85b34423da47 Mon Sep 17 00:00:00 2001
From: Christian Pointner <equinox@anytun.org>
Date: Sun, 17 Sep 2017 15:15:31 +0200
Subject: minor refactoring

---
 satp/crypto-kd.go | 43 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 11 deletions(-)

diff --git a/satp/crypto-kd.go b/satp/crypto-kd.go
index 208c4a9..b2b63df 100644
--- a/satp/crypto-kd.go
+++ b/satp/crypto-kd.go
@@ -35,21 +35,42 @@ type KeyUsage int
 type Label uint32
 
 const (
-	KeyLeft KeyDirection = iota
-	KeyRight
+	DirLeft KeyDirection = iota
+	DirRight
 
-	Encrypt KeyUsage = iota
-	Salt
-	Auth
+	UsageEncryptKey KeyUsage = iota
+	UsageEncryptSalt
+	UsageAuthKey
 
-	LabelLeftEncrypt  = 0x356A192B
-	LabelRightEncrypt = 0xDA4B9237
-	LabelLeftSalt     = 0x77DE68DA
-	LabelRightSalt    = 0x1B645389
-	LabelLeftAuth     = 0xAC3478D6
-	LabelRightAuth    = 0xC1DFD96E
+	LabelLeftEncrypt      = 0x356A192B
+	LabelRightEncrypt     = 0xDA4B9237
+	LabelLeftEncryptSalt  = 0x77DE68DA
+	LabelRightEncryptSalt = 0x1B645389
+	LabelLeftAuthKey      = 0xAC3478D6
+	LabelRightAuthKey     = 0xC1DFD96E
 )
 
 type KeyDerivation interface {
 	Generate(dir KeyDirection, usage KeyUsage, sequenceNumber uint32) ([]byte, error)
 }
+
+func getLabel(dir KeyDirection, usage KeyUsage) uint32 {
+	switch usage {
+	case UsageEncryptKey:
+		if dir == DirLeft {
+			return LabelLeftEncrypt
+		}
+		return LabelRightEncrypt
+	case UsageEncryptSalt:
+		if dir == DirLeft {
+			return LabelLeftEncryptSalt
+		}
+		return LabelRightEncryptSalt
+	case UsageAuthKey:
+		if dir == DirLeft {
+			return LabelLeftAuthKey
+		}
+		return LabelRightAuthKey
+	}
+	panic("Key-derivation: invalid direction and/or usage")
+}
-- 
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