Securing Data Authentication Securing Data Authentication with with Cryptographic Signatures in Cryptographic Signatures in

BitTorrentBitTorrent

Du Weiwedu @ cc.hut.fi / wei.du@hiit.fi

Supervisor : Professor Jukka Manner Instructor : Professor Sasu Tarkoma

Msc. Petri Savolainen

25-08-2009

Helsinki University of Technology, FinlandDepartment of Communications and Networking

OverviewOverview

1.Introduction

2.Background

3.Implemetation

4.Expermental Results and Analysis

5.Conclusion

Peer-to-Peer File Sharing systemsPeer-to-Peer File Sharing systems

Fast Growing Uses : Audio and Video files

A major part of traffic on the Internet

Different from Client/Server File Sharing systems

1. INTRODUCTION1. INTRODUCTION

BitTorrent BitTorrent   

A Peer-to-Peer File Sharing system 

The most popular P2P protocol worldwide 

Millions of users  

Critical ElementsA Web Server: provides the ‘metainfo’ file by HTTP

The .torrent File: contains ‘metainfo’ information (File name, size, checksum, URL of the Tracker, Pieces <hash1,hash2,….hashn>, Piece length )

A BitTorrent Tracker: manage the list of peers

Peers:

seeds: have the entire fileleechers: still downloading, also called downloaders.Free-riders: only download from others but do not upload

How BitTorrent Works?How BitTorrent Works?

Leecher A

Seed

Leecher B

Tracker

Web Server

1. O

btai

n.to

rren

t file

2. Contact the Tracker (U

RL) Get-announce

3. Obtain a peer list (c

ontains seeds &

leechers)

4. Shake-hand

4. Shake-hand

5. Get pieces

5.Get Pieces

BitTorrent   

Messages Peer - Peer Messages: TCP Sockets

Peer - Tracker Messages: HTTP Request/Response

File Organization

A PieceChunk size=256KB

A Block(subpiece)

16KB

File

421 3

Incomplete Piece

Piece Hash Value (SHA1)Size=20Bytes

How to validate dataGenerate piece hashes by SHA1 hashing algorithm

Save piece hashes in .torrent file

Seed will check if hashes are matched before upload the file

Leecher will verify data with hashes in .torrent file when each chunk is downloaded in parallel

Problems to AddressPiece hashes in .torrent file are not secure enough.

The size of .torrent file grows, when the file size increases.

Especially, when the chunk size (piece size) is small.

In P2P live streaming, the chunk size is smaller, the speed is faster. However, the chunk sizes are always large.

2. BACKGROUND2. BACKGROUND

Related WorkHash tree : simple but infeasible for a latency sensitive communication

Hash chain : lightweight but more complex schemes

Cryptographic Signatures AlgorithmsRSA (Rivest-Shamir-Adleman)

DSA (Digital Signature Algorithm)

ECDSA (Elliptic Curve Digital Signature Algorithm)

3. IMPELEMENTATION3. IMPELEMENTATION

3.1 Design

DSA

ECDSA

RSA

Key Pair

Step 1- Generate Key Pair by using Cryptographic

Algorithms

Step 2- Create signatures for .sig file with Private key

Save Public key in .torrent file

Step 3- Verify Signatures with Public key

Public keys are saved in the .torrent file with different Cryptographic Algorithm (Using Openssl library)

RSA : n, e

DSA : p, q, g

ECDSA : ecp

Adding SIGNATURE message in BitTorrent Protocol

Policy: Once downloading a piece completely, the peer can authenticate it efficiently right away.

This policy lets complete pieces could be authenticated quickly, even for smaller piece sizes (large piece numbers)

In order to keep the .torrent file smaller, we save the signatures in a .sig file separately and send corresponding signature separately before a piece is sent.

SIGNATURE:<len=005+X>< id=88><piece_index><signature>Payload Information:

len : (32 bits integer)

id : (32 bits integer)

piece_index : (32 bits integer)

signature : (X bytes)

3.2 SIGNATURE Message

4. 4. EXPERIMENTAL RESULTS AND ANALYSISEXPERIMENTAL RESULTS AND ANALYSIS

Hardware:2 Desktop PCs

1 Switch

Software:Ubuntu 9.04

Ktorrent 3.2.1

Openssl 0.9.8g

Wondershaper 1.0

4.1 Lab Environments

  PC1 PC2CPU Intel(R) Core(TM)2

Duo CPU E6750 @ 2.66GHz

Intel(R) Core(TM)2 Quad CPU Q9300 @ 2.50GHz

Memory 4GB 8GBNIC Intel Corporation

82566DM-2 Gigabit Ethernet

Broadcom Corporation NetXtreme BCM5754 Gigabit Ethernet

  i686 GNU/Linux x86_64 GNU/Linux

Signature Size (Chunk size=32KB)

4.2 Experimental Results

Key SizeKey Size 512(bit)512(bit) 1024(bit)1024(bit) 2048 (bit)2048 (bit) 3072(bit)3072(bit)

RSA Signature (Bytes)RSA Signature (Bytes) 6464 128128 256256 384384DSA Signature(Bytes)DSA Signature(Bytes) 4848 4848 4848 4848

Size (Bytes)Size (Bytes) ECSDA Secp-160r1ECSDA Secp-160r1 ECDSA Secp-224r1ECDSA Secp-224r1

ECC SignatureECC Signature 4242 5656

ECC 160bit = RSA 1024bit (algorithms strengths)

ECC 224bit = RSA 2048bit (algorithms strengths)

Signing and Verifying Time of Openssl PC1     Sign(ms) Verify(ms) Sign/s Verify/s

rsa 512 bits 0.446 0.033 2243.1 30283.3rsa 1024 bits 1.998 0.086 500.6 11679.6rsa 2048 bits 10.756 0.269 93.0 3723.2rsa 4096 bits 64.196 0.873 15.58 1145.8dsa 512 bits 0.345 0.410 2894.8 2440.3dsa 1024 bits 0.864 1.013 1157.8 987.2dsa 2048 bits 2.690 3.224 371.7 310.2ecdsa(secp160r1) 160 bits 0.3 1.4 3518.4 719.4ecdsa(secp224r1) 224 bits 1.5 1.7 677.9 576.37

 PC2     Sign(ms) Verify(ms) Sign/s Verify/s

rsa 512 bits 0.229 0.016 4359,3 63609rsa 1024 bits 0.897 0.043 1115,2 23120,2rsa 2048 bits 5.061 0.136 197,6 7338,4rsa 4096 bits 32.323 0.467 30,9 2140,9dsa 512 bits 0.158 0.174 6320,2 5731,8dsa 1024 bits 0.418 0.492 2394,5 2034,5dsa 2048 bits 1.325 1.578 754,8 633,8ecdsa(secp160r1) 160 bits 0.200 0.700 6285,5 1424,3ecdsa(secp224r1) 224 bits 0.700 1.100 1428,571 937,8

Average Download Speed (MB/s) : PC2, PC2, File File Size =150MBSize =150MB

Max Download Speed = 10MB/s, Max Upload Speed =10MB/s, Chunk size=32KB Max Download Speed = 10MB/s, Max Upload Speed =10MB/s, Chunk size=32KB  Average Download Speed (MB/s) Average Download Speed (MB/s)

 Algorithms/Key Size (bit) 512 1024 2048 3072

RSA 9,05 8,89 8,77 8,60

DSA 8,85 8,53 8,38 8,15

ECDSA(spec160r1/spec224r1)   9,00 8,80  

No Signature 9,23 9,23 9,23 9,23

Max Download Speed =128KB/s, Max Upload Speed =128KB/s, Max Download Speed =128KB/s, Max Upload Speed =128KB/s, Chunk size=32KBChunk size=32KB Average Download Speed (KB/s) Average Download Speed (KB/s)

 Algorithms/Key Size (bit) 512 1024 2048 3072

RSA 120,85 120,41 119,33 118,65

DSA 120,75 120,84 120,72 120,68

ECDSA(spec160r1/spec224r1) 120,89 120,75  

No Signature 121,43 121,43 121,43 121,43

4.3 Data AnalysisMax Download Speed Max Download Speed =10MB, 150MB File Size, Chunk size=32KB =10MB, 150MB File Size, Chunk size=32KB

Max Download Speed Max Download Speed =128KB, 150MB File Size, Chunk size=32KB =128KB, 150MB File Size, Chunk size=32KB

RSA is faster than DSA when Max download speed is 10MB

But RSA is slower than DSA when Max donwload speed is 128KB

Signature size is smaller, average download speed is faster, when bandwidth is small.

Verify time is faster, average download speed is faster, when bandwidth is large.

ECC is faster due to its small signature size, although it’s slower to verify

5. Conclusion5. Conclusion

P2P Networks P2P Networks Millions of UsersMillions of Users

Secure, Efficient, Secure, Efficient, Energy saving… Energy saving…

VoIP

BitTorrent

TCP

http

ServicesServices

Thank You!