diff --git a/app/src/main/java/com/samourai/wallet/segwit/bech32/Bech32Segwit.java b/app/src/main/java/com/samourai/wallet/segwit/bech32/Bech32Segwit.java
index dda9e8bd4..decf0f14f 100644
--- a/app/src/main/java/com/samourai/wallet/segwit/bech32/Bech32Segwit.java
+++ b/app/src/main/java/com/samourai/wallet/segwit/bech32/Bech32Segwit.java
@@ -2,10 +2,6 @@
 
 import org.apache.commons.lang3.tuple.Pair;
 
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-
 public class Bech32Segwit {
 
     public static Pair<Byte, byte[]> decode(String hrp, String addr) throws Exception {
@@ -24,11 +20,8 @@ public static Pair<Byte, byte[]> decode(String hrp, String addr) throws Exceptio
         }
 
         byte[] data = p.getRight();
-        List<Byte> progBytes = new ArrayList<Byte>();
-        for(int i = 1; i < data.length; i++) {
-            progBytes.add(data[i]);
-        }
-        byte[] decoded = convertBits(progBytes, 5, 8, false);
+        byte[] decoded = new byte[getOutSize(data.length - 1, 5, 8, false)];
+        convertBits(data, 1, decoded, 0, 5, 8, false);
         if(decoded.length < 2 || decoded.length > 40)   {
             throw new Exception("invalid decoded data length");
         }
@@ -47,32 +40,32 @@ public static Pair<Byte, byte[]> decode(String hrp, String addr) throws Exceptio
 
     public static String encode(String hrp, byte witnessVersion, byte[] witnessProgram) throws Exception    {
 
-        List<Byte> progBytes = new ArrayList<Byte>();
-        for(int i = 0; i < witnessProgram.length; i++) {
-            progBytes.add(witnessProgram[i]);
-        }
-
-        byte[] prog = convertBits(progBytes, 8, 5, true);
-        byte[] data = new byte[1 + prog.length];
-
-        System.arraycopy(new byte[] { witnessVersion }, 0, data, 0, 1);
-        System.arraycopy(prog, 0, data, 1, prog.length);
+        byte[] data = new byte[1 + getOutSize(witnessProgram.length, 8, 5, true)];
+        data[0] = witnessVersion;
+        convertBits(witnessProgram, 0, data, 1, 8, 5, true);
 
         String ret = Bech32.bech32Encode(hrp, data);
 
         return ret;
     }
 
-    private static byte[] convertBits(List<Byte> data, int fromBits, int toBits, boolean pad) throws Exception    {
+    private static int getOutSize(int dataSize, int fromBits, int toBits, boolean pad) {
+        int outSize = dataSize * fromBits / toBits;
+        if (pad && outSize * toBits < dataSize * fromBits) {
+            outSize++;
+        }
+        return outSize;
+    }
+
+    private static void convertBits(byte[] src, int srcIdx, byte[] dest, int destIdx,
+                                    int fromBits, int toBits, boolean pad) throws Exception    {
 
         int acc = 0;
         int bits = 0;
         int maxv = (1 << toBits) - 1;
-        List<Byte> ret = new ArrayList<Byte>();
-
-        for(Byte value : data)  {
 
-            short b = (short)(value.byteValue() & 0xff);
+        for(; srcIdx < src.length; srcIdx++) {
+            short b = (short)(src[srcIdx] & 0xff);
 
             if (b < 0) {
                 throw new Exception();
@@ -88,26 +81,19 @@ else if ((b >> fromBits) > 0) {
             bits += fromBits;
             while (bits >= toBits)  {
                 bits -= toBits;
-                ret.add((byte)((acc >> bits) & maxv));
+                dest[destIdx++] = (byte)((acc >> bits) & maxv);
             }
         }
 
         if(pad && (bits > 0))    {
-            ret.add((byte)((acc << (toBits - bits)) & maxv));
+            dest[destIdx++] = (byte)((acc << (toBits - bits)) & maxv);
         }
         else if (bits >= fromBits || (byte)(((acc << (toBits - bits)) & maxv)) != 0)    {
-            return null;
+            throw new Exception();
         }
         else    {
             ;
         }
-
-        byte[] buf = new byte[ret.size()];
-        for(int i = 0; i < ret.size(); i++) {
-            buf[i] = ret.get(i);
-        }
-
-        return buf;
     }
 
     public static byte[] getScriptPubkey(byte witver, byte[] witprog) {