diff --git a/src/clientP2P/ClientManagementTCP.java b/src/clientP2P/ClientManagementTCP.java
index c7c16e6..b160d26 100644
--- a/src/clientP2P/ClientManagementTCP.java
+++ b/src/clientP2P/ClientManagementTCP.java
@@ -229,6 +229,17 @@ public class ClientManagementTCP implements Runnable {
 		} while(!fileFullyWritten);
 		if (!Arrays.equals(hash512, computeHashsum(filename, HashAlgorithm.SHA512))) {
 			System.err.println("Error: Hashsum does not match");
+			System.err.println("Computed checksum:");
+			byte[] c = computeHashsum(filename, HashAlgorithm.SHA512);
+			for (byte b: c) {
+				System.err.print(String.format("%02X", b));
+			}
+			System.err.println("");
+			System.err.println("Received checksum:");
+			for (byte b: hash512) {
+				System.err.print(String.format("%02X", b));
+			}
+			System.err.println("");
 			throw new InternalError();
 		}
 		socket.close();
diff --git a/src/clientP2P/ClientManagementUDP.java b/src/clientP2P/ClientManagementUDP.java
index 4d92f84..83b3d7b 100644
--- a/src/clientP2P/ClientManagementUDP.java
+++ b/src/clientP2P/ClientManagementUDP.java
@@ -216,6 +216,17 @@ public class ClientManagementUDP implements Runnable {
 		} while(!fileFullyWritten);
 		if (!Arrays.equals(hash512, computeHashsum(filename, HashAlgorithm.SHA512))) {
 			System.err.println("Error: Hashsum does not match");
+			System.err.println("Computed checksum:");
+			byte[] c = computeHashsum(filename, HashAlgorithm.SHA512);
+			for (byte b: c) {
+				System.err.print(String.format("%02X", b));
+			}
+			System.err.println("");
+			System.err.println("Received checksum:");
+			for (byte b: hash512) {
+				System.err.print(String.format("%02X", b));
+			}
+			System.err.println("");
 			throw new InternalError();
 		}
 	}
diff --git a/src/protocolP2P/FileList.java b/src/protocolP2P/FileList.java
index bc2ca69..1c04f30 100644
--- a/src/protocolP2P/FileList.java
+++ b/src/protocolP2P/FileList.java
@@ -7,6 +7,7 @@ import exception.ProtocolError;
 import exception.InternalError;
 import exception.SizeError;
 import java.io.UnsupportedEncodingException;
+import tools.BytesArrayTools;
 
 /** Representation of payload for list response.
  * @author	Louis Royer
@@ -48,11 +49,7 @@ public class FileList extends Payload {
 			throw new InternalError();
 		}
 		int size = getPayloadSize(packet);
-		try {
-			fileList = (new String(packet, PAYLOAD_START_POSITION, size, "UTF-8")).split("\n");
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		fileList = BytesArrayTools.readStringArray(packet, PAYLOAD_START_POSITION, size, "\n");
 	}
 
 	/** Returns a byte[] containing Packet with padding.
@@ -63,40 +60,14 @@ public class FileList extends Payload {
 	 */
 	protected byte[] toPacket() throws InternalError {
 		// compute size
-		int size = PAYLOAD_START_POSITION;
-		for (String s : fileList) {
-			size += s.length();
-			size += 1; // size for '\n'
-		}
-		size -=1; // remove trailing '\n'
+		int size = PAYLOAD_START_POSITION + BytesArrayTools.computeStringArraySize(fileList, "\n");
 		byte[] packet = new byte[size]; // java initialize all to zero
 		// set request/response code
 		packet[RequestResponseCode.RRCODE_POSITION] = requestResponseCode.codeValue;
 		// set payload size
 		setPayloadSize(size - PAYLOAD_START_POSITION, packet);
 		// Write fileList
-		int bCount = PAYLOAD_START_POSITION;
-		for(String s : fileList) {
-			if (bCount != PAYLOAD_START_POSITION) { // not on first iteration
-				try {
-					packet[bCount] = "\n".getBytes("UTF-8")[0]; // separator
-				} catch (UnsupportedEncodingException e) {
-					throw new InternalError();
-				}
-				bCount += 1;
-			}
-			// Copy filename
-			try {
-				byte[] sb = s.getBytes("UTF-8");
-				for(byte b : sb) {
-					packet[bCount] = b;
-					bCount += 1;
-				}
-			} catch (UnsupportedEncodingException e) {
-				throw new InternalError();
-			}
-			
-		}
+		BytesArrayTools.write(packet, fileList, PAYLOAD_START_POSITION, "\n");
 		return packet;
 	}
 
diff --git a/src/protocolP2P/FilePart.java b/src/protocolP2P/FilePart.java
index 2e2a211..df5699f 100644
--- a/src/protocolP2P/FilePart.java
+++ b/src/protocolP2P/FilePart.java
@@ -90,22 +90,11 @@ public class FilePart extends Payload {
 		BytesArrayTools.write(packet, TOTAL_FILESIZE_POSITION, totalSize);
 		// write filename’s size to Packet
 		BytesArrayTools.write(packet, FILENAME_SIZE_POSITION, filename.length());
-		try {
-			// write filename to Packet
-			int i = FILENAME_POSITION;
-			for (byte b : filename.getBytes("UTF-8")) {
-				packet[i] = b;
-				i += 1;
-			}
-			// write partialContent to Packet
-			for (byte b: partialContent) {
-				packet[i] = b;
-				i += 1;
-			}
-			return packet;
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		// write filename to Packet
+		BytesArrayTools.write(packet, filename, FILENAME_POSITION);
+		// write partialContent to  Packet
+		BytesArrayTools.write(packet, partialContent, FILENAME_POSITION + filename.length());
+		return packet;
 	}
 
 	/** Write from Packet into offset.
@@ -150,11 +139,7 @@ public class FilePart extends Payload {
 	 */
 	private void setFilename(byte[] packet) throws ProtocolError, SizeError, InternalError {
 		int filenameSize = getFilenameSize(packet); // this can throw ProtocolError or SizeError
-		try {
-			filename = new String(packet, FILENAME_POSITION, filenameSize, "UTF-8");
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		filename = BytesArrayTools.readString(packet, FILENAME_POSITION, filenameSize);
 	}
 
 	/** Write from Packet into partialContent.
@@ -165,11 +150,7 @@ public class FilePart extends Payload {
 	private void setPartialContent(byte[] packet) throws ProtocolError, SizeError {
 		int start = FILENAME_POSITION + getFilenameSize(packet); // this can throw SizeError or ProtocolError
 		int end = OFFSET_POSITION + getPayloadSize(packet); // this can throw SizeError
-		try {
-			partialContent = Arrays.copyOfRange(packet, start, end);
-		} catch (ArrayIndexOutOfBoundsException e) {
-			throw new ProtocolError();
-		}
+		partialContent = BytesArrayTools.readByteArray(packet, start, end);
 	}
 
 	/** partialContent getter.
diff --git a/src/protocolP2P/HashRequest.java b/src/protocolP2P/HashRequest.java
index 8caf2d7..92ab812 100644
--- a/src/protocolP2P/HashRequest.java
+++ b/src/protocolP2P/HashRequest.java
@@ -60,23 +60,18 @@ public class HashRequest extends Payload {
 		}
 		/* Read filename */
 		int filenameSize = BytesArrayTools.readInt(packet, FILENAME_SIZE_POSITION);
-		try {
-			filename = new String(packet, FILENAME_POSITION, filenameSize, "UTF-8");
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
 
+		/* Read filename */
+		filename = BytesArrayTools.readString(packet, FILENAME_POSITION, filenameSize);
+
+		/* Read algo list */
 		int size = getPayloadSize(packet);
-		try {
-			String[] l = (new String(packet, FILENAME_POSITION + filenameSize, size, "UTF-8")).split("\n");
-			int i = 0;
-			algoList = new HashAlgorithm[l.length];
-			for(String algo : l) {
-				algoList[i] = HashAlgorithm.fromName(algo);
-				i++;
-			}
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
+		String[] algoListStr = BytesArrayTools.readStringArray(packet, FILENAME_POSITION + filenameSize, size, "\n");
+		int i = 0;
+		algoList = new HashAlgorithm[algoListStr.length];
+		for(String algo : algoListStr) {
+			algoList[i] = HashAlgorithm.fromName(algo);
+			i++;
 		}
 	}
 
@@ -89,63 +84,24 @@ public class HashRequest extends Payload {
 	protected byte[] toPacket() throws InternalError {
 		// compute size
 		int filenameSize = filename.length();
-		int size = FILENAME_POSITION + filenameSize;
+		String[] algoListStr = new String[algoList.length];
+		int i = 0;
 		for (HashAlgorithm h : algoList) {
-			if (h == null) {
-				continue;
-			}
-			size += h.getName().length();
-			size += 1; // size for '\n'
+			algoListStr[i] = h.getName();
+			i++;
 		}
-		size -=1; // remove trailing '\n'
+		int size = FILENAME_POSITION + filenameSize + BytesArrayTools.computeStringArraySize(algoListStr, "\n");
 		byte[] packet = new byte[size + 1]; // java initialize all to zero
-		
 		// set request/response code
 		packet[RequestResponseCode.RRCODE_POSITION] = requestResponseCode.codeValue;
-		
 		// set Payload size
 		setPayloadSize(size - FILENAME_SIZE_POSITION, packet);
-
+		// write filename size
 		BytesArrayTools.write(packet, FILENAME_SIZE_POSITION, filenameSize);
-		
-		// Write filename
-		int bCount = FILENAME_POSITION;
-		try {
-			byte[] sb = filename.getBytes("UTF-8");
-			for(byte b : sb) {
-				packet[bCount] = b;
-				bCount += 1;
-			}
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
-		boolean firstIter = true;
-		for(HashAlgorithm h : algoList) {
-			if (h == null) {
-				continue;
-			}
-			String s = h.getName();
-			if (!firstIter) {
-				firstIter = false;
-				try {
-					packet[bCount] = "\n".getBytes("UTF-8")[0]; // separator
-				} catch (UnsupportedEncodingException e) {
-					throw new InternalError();
-				}
-				bCount += 1;
-			}
-			// Copy algoname
-			try {
-				byte[] sb = s.getBytes("UTF-8");
-				for(byte b : sb) {
-					packet[bCount] = b;
-					bCount += 1;
-				}
-			} catch (UnsupportedEncodingException e) {
-				throw new InternalError();
-			}
-			
-		}
+		// write filename
+		BytesArrayTools.write(packet, filename, FILENAME_POSITION);
+		// write algo list
+		BytesArrayTools.write(packet, algoListStr, FILENAME_POSITION + filename.length(), "\n");
 		return packet;
 	}
 
diff --git a/src/protocolP2P/HashResponse.java b/src/protocolP2P/HashResponse.java
index 64ea71c..2ff0440 100644
--- a/src/protocolP2P/HashResponse.java
+++ b/src/protocolP2P/HashResponse.java
@@ -63,33 +63,22 @@ public class HashResponse extends Payload {
 		}
 		/* Read filename */
 		int filenameSize = BytesArrayTools.readInt(packet, FILENAME_SIZE_POSITION);
-		try {
-			filename = new String(packet, FILENAME_POSITION, filenameSize, "UTF-8");
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		filename = BytesArrayTools.readString(packet, FILENAME_POSITION, filenameSize);
 
 		int size = getPayloadSize(packet);
 		int start = FILENAME_POSITION + filenameSize;
 		do {
 			int algoNameSize = BytesArrayTools.readInt(packet, start);
 			start +=4;
-			try {
-				String algoName = new String(packet, start, algoNameSize, "UTF-8");
-				start += algoNameSize;
-				int hashSize = BytesArrayTools.readInt(packet, start);
-				start += 4;
-				if (hashSize != 0) {
-					byte[] b = new byte[hashSize];
-					for (int i=0;i<hashSize;i++) {
-						b[i] = packet[start+i];
-					}
-					hashes.put(HashAlgorithm.fromName(algoName), b);
-				}
-				start += hashSize;
-			} catch (UnsupportedEncodingException e) {
-				throw new InternalError();
+			String algoName = BytesArrayTools.readString(packet, start, algoNameSize);
+			start += algoNameSize;
+			int hashSize = BytesArrayTools.readInt(packet, start);
+			start += 4;
+			if (hashSize != 0) {
+				byte[] b = BytesArrayTools.readByteArray(packet, start, start+hashSize);
+				hashes.put(HashAlgorithm.fromName(algoName), b);
 			}
+			start += hashSize;
 		} while (start < size);
 			
 	}
@@ -114,49 +103,28 @@ public class HashResponse extends Payload {
 		
 		// set request/response code
 		packet[RequestResponseCode.RRCODE_POSITION] = requestResponseCode.codeValue;
-		
 		// set Payload size
 		setPayloadSize(size - FILENAME_SIZE_POSITION, packet);
-
+		// write filename size
 		BytesArrayTools.write(packet, FILENAME_SIZE_POSITION, filenameSize);
-		
-		// Write filename
-		int bCount = FILENAME_POSITION;
-		try {
-			byte[] sb = filename.getBytes("UTF-8");
-			for(byte b : sb) {
-				packet[bCount] = b;
-				bCount += 1;
-			}
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		// write filename
+		BytesArrayTools.write(packet, filename, FILENAME_POSITION);
+		int bCount = FILENAME_POSITION + filename.length();
 		for(HashAlgorithm h : hashes.keySet()) {
 			String s = h.getName();
 			BytesArrayTools.write(packet, bCount, (int)s.length());
 			bCount += 4;
-			// Copy algoname
-			try {
-				byte[] sb = s.getBytes("UTF-8");
-				for(byte b : sb) {
-					packet[bCount] = b;
-					bCount += 1;
-				}
-			} catch (UnsupportedEncodingException e) {
-				throw new InternalError();
-			}
+			// write algoname
+			BytesArrayTools.write(packet, s, bCount);
+			bCount += s.length();
+			// write hash size
 			byte[] hashb = hashes.get(HashAlgorithm.fromName(s));
-			if (hashb.length == 0) {
-				BytesArrayTools.write(packet, bCount, (int)0);
-				bCount += 4;
-			} else {
-				BytesArrayTools.write(packet, bCount, (int)hashb.length);
-				bCount +=4;
-				// copy hash
-				for(byte b : hashb) {
-					packet[bCount] = b;
-					bCount += 1;
-				}
+			BytesArrayTools.write(packet, bCount, (int)hashb.length);
+			bCount += 4;
+			if (hashb.length != 0) {
+				// write hash
+				BytesArrayTools.write(packet, hashb, bCount);
+				bCount += hashb.length;
 			}
 		}
 		return packet;
diff --git a/src/protocolP2P/LoadRequest.java b/src/protocolP2P/LoadRequest.java
index 39c4952..4017cb0 100644
--- a/src/protocolP2P/LoadRequest.java
+++ b/src/protocolP2P/LoadRequest.java
@@ -64,11 +64,7 @@ public class LoadRequest extends Payload {
 		
 		/* Read filename */
 		int size = BytesArrayTools.readInt(packet, FILENAME_SIZE_POSITION);
-		try {
-			filename = new String(packet, FILENAME_POSITION, size, "UTF-8");
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		filename = BytesArrayTools.readString(packet, FILENAME_POSITION, size);
 	}
 
 	/** Returns a byte[] containing Packet with padding.
@@ -82,33 +78,18 @@ public class LoadRequest extends Payload {
 		int filenameSize = filename.length();
 		int size = FILENAME_POSITION + filenameSize;
 		byte[] packet = new byte[size + 1]; // java initialize all to zero
-		
 		// set request/response code
 		packet[RequestResponseCode.RRCODE_POSITION] = requestResponseCode.codeValue;
-		
 		// set Payload size
 		setPayloadSize(size - OFFSET_POSITION, packet);
-
 		// Write offset
 		BytesArrayTools.write(packet, OFFSET_POSITION, (long)offset);
-
 		// Write maxSizePartialContent
 		BytesArrayTools.write(packet, MAX_SIZE_PARTIAL_CONTENT_POSITION, (long)maxSizePartialContent);
-
 		// Write filenameSize
 		BytesArrayTools.write(packet, FILENAME_SIZE_POSITION, (int)filenameSize);
-		
 		// Write filename
-		int bCount = FILENAME_POSITION;
-		try {
-			byte[] sb = filename.getBytes("UTF-8");
-			for(byte b : sb) {
-				packet[bCount] = b;
-				bCount += 1;
-			}
-		} catch (UnsupportedEncodingException e) {
-			throw new InternalError();
-		}
+		BytesArrayTools.write(packet, filename, FILENAME_POSITION);
 		return packet;
 	}
 
diff --git a/src/tools/BytesArrayTools.java b/src/tools/BytesArrayTools.java
index 924f4fc..c11088c 100644
--- a/src/tools/BytesArrayTools.java
+++ b/src/tools/BytesArrayTools.java
@@ -1,5 +1,10 @@
 package tools;
 import exception.SizeError;
+import exception.ProtocolError;
+import java.io.UnsupportedEncodingException;
+import java.util.Arrays;
+
+
 /** Helper to manipulate byte[].
  * @author	Louis Royer
  * @author	Flavien Haas
@@ -116,4 +121,129 @@ public class BytesArrayTools {
 		}
 		return new String(bArray, 0, cpt + 1);
 	}
+
+	/** Write a list of string to a byte array. String are separated by a separator.
+	 * @param byteArray	array to write
+	 * @param strArray	string array to read
+	 * @param start	start position to write in byteArray
+	 * @param separator	separator to use
+	 * @throws	InternalError
+	 */
+	public static void write(byte[] byteArray, String[] strArray, int start, String separator) throws InternalError {
+		int bCount = start;
+		try {
+			byte[] sepb = separator.getBytes("UTF-8");
+			for(String s : strArray) {
+				// write separator
+				if (bCount != start) { // not on first iteration
+					for (byte b : sepb) {
+						byteArray[bCount] = b;
+						bCount += 1;
+					}
+				}
+				// Copy string
+				byte[] sb = s.getBytes("UTF-8");
+				for(byte b : sb) {
+					byteArray[bCount] = b;
+					bCount += 1;
+				}
+			}
+		} catch (UnsupportedEncodingException e) {
+			throw new InternalError();
+		}
+	}
+
+	/** Read string array from byte array starting at start with size parameter.
+	 * @param byteArray	Array to read
+	 * @param start	Start position
+	 * @param size	Size to read
+	 * @param separator	Separator used
+	 * @return	String array output
+	 * @throws	InternalError
+	 */
+	public static String[] readStringArray(byte[] byteArray, int start, int size, String separator) throws InternalError {
+		try {
+			return (new String(byteArray, start, size, "UTF-8")).split(separator);
+		} catch (UnsupportedEncodingException e) {
+			throw new InternalError();
+		}
+	}
+
+	/** Compute size of string array once converted to byte array with separator
+	 * @param strArray	String Array
+	 * @param separator	Separator used
+	 * @return	size
+	 */
+	public static int computeStringArraySize(String[] strArray, String separator) {
+		int size = 0;
+		for (String s: strArray) {
+			if (size != 0) {
+				size += separator.length();
+			}
+			size += s.length();
+		}
+		return size;
+	}
+
+	/** Write a string to a byte array.
+	 * @param array	Byte Array to write
+	 * @param str	String to read
+	 * @param start	Start position in byte array to write
+	 * @throws	InternalError
+	 */
+	public static void write(byte[] array, String str, int start) throws InternalError {
+		int bCount = start;
+		try {
+			byte[] sb = str.getBytes("UTF-8");
+			for(byte b : sb) {
+				array[bCount] = b;
+				bCount += 1;
+			}
+		} catch (UnsupportedEncodingException e) {
+			throw new InternalError();
+		}
+	}
+
+	/** Read string from byte array
+	 * @param array	Byte array to read
+	 * @param start	start position in byte array
+	 * @param size	size to read
+	 * @return	String read
+	 * @throws	InternalError
+	 */
+	public static String readString(byte[] array, int start, int size) throws InternalError {
+		try {
+			return new String(array, start, size, "UTF-8");
+		} catch (UnsupportedEncodingException e) {
+			throw new InternalError();
+		}
+	}
+
+	/** Write byte Array to byte Array.
+	 * @param dst	Destination byte Array
+	 * @param src	Source byte Array
+	 * @param start	Start in dest array
+	 */
+	public static void write(byte[] dst, byte[] src, int start) {
+		int i = start;
+		for (byte b: src) {
+			dst[i] = b;
+			i += 1;
+		}
+	}
+
+	/** Read byte Array to byte Array
+	 * @param src	Source byte Array
+	 * @param start	Start position in source
+	 * @param end	End position in source
+	 * @return	Resulting byte array
+	 * @throws	ProtocolError
+	 */
+	public static byte[] readByteArray(byte[] src, int start, int end) throws ProtocolError {
+		try {
+			return Arrays.copyOfRange(src, start, end);
+		} catch (ArrayIndexOutOfBoundsException e) {
+			throw new ProtocolError();
+		}
+	}
 }