Securing Data Authentication with Cryptographic Signatures in BitTorrent Du Wei cc.hut.fi / Supervisor : Professor Jukka Manner Instructor : Professor Sasu Tarkoma Msc. Petri Savolainen Helsinki University of Technology, Finland Department of Communications and Networking

Overview Overview 1.Introduction 2.Background 3.Implemetation 4.Expermental Results and Analysis 5.Conclusion

Peer-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. INTRODUCTION

BitTorrent BitTorrent A Peer-to-Peer File Sharing system The most popular P2P protocol worldwide Millions of users Critical Elements A Web Server : provides the ‘ metainfo ’ file by HTTP The.torrent File : contains ‘ metainfo ’ information (File name, size, checksum, URL of the Tracker, Pieces, Piece length ) A BitTorrent Tracker: manage the list of peers Peers : seeds : have the entire file leechers : still downloading, also called d ownloaders. Free-riders: only download from others but do not upload

How BitTorrent Works? Leecher A Seed Leecher B Tracker Web Server 1. Obtain.torrent file 2. Contact the Tracker (URL) Get-announce 3. Obtain a peer list (contains seeds & leechers) 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 Piece Chunk size=256KB A Block (subpiece) 16KB File Incomplete Piece Piece Hash Value (SHA1) Size=20Bytes

How to validate data Generate 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 Address Piece 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. BACKGROUND Related Work Hash tree : simple but infeasible for a latency sensitive communication Hash chain : lightweight but more complex schemes Cryptographic Signatures Algorithms RSA (Rivest-Shamir-Adleman) DSA (Digital Signature Algorithm) ECDSA (Elliptic Curve Digital Signature Algorithm)

3. 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: Payload Information: len : (32 bits integer) id : (32 bits integer) piece_index : (32 bits integer) signature : (X bytes) 3.2 SIGNATURE Message

4. EXPERIMENTAL RESULTS AND ANALYSIS Hardware: 2 Desktop PCs 1 Switch Software: Ubuntu 9.04 Ktorrent Openssl 0.9.8g Wondershaper Lab Environments PC1PC2 CPU Intel(R) Core(TM)2 Duo CPU 2.66GHz Intel(R) Core(TM)2 Quad CPU 2.50GHz Memory4GB8GB NIC 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 Size 512(bit) 1024(bit) 2048 (bit) 3072(bit) RSA Signature (Bytes) DSA Signature(Bytes) Size (Bytes) ECSDA Secp-160r1 ECDSA Secp-224r1 ECC Signature 4256 ECC 160bit = RSA 1024bit (algorithms strengths) ECC 224bit = RSA 2048bit (algorithms strengths)

Signing and Verifying Time of Openssl PC1 Sign(ms)Verify(ms)Sign/sVerify/s rsa512bits rsa1024bits rsa2048bits rsa4096bits dsa512bits dsa1024bits dsa2048bits ecdsa(secp160r1)160bits ecdsa(secp224r1)224bits PC2 Sign(ms)Verify(ms)Sign/sVerify/s rsa512bits , rsa1024bits ,223120,2 rsa2048bits ,67338,4 rsa4096bits ,92140,9 dsa512bits ,25731,8 dsa1024bits ,52034,5 dsa2048bits ,8633,8 ecdsa(secp160r1)160bits ,51424,3 ecdsa(secp224r1)224bits ,571937,8

PC2, File Size =150MB Average Download Speed (MB/s) : PC2, File Size =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) Algorithms/Key Size (bit) RSA9,058,898,778,60 DSA8,858,538,388,15 ECDSA(spec160r1/spec224r1) 9,008,80 No Signature9,23 Max Download Speed =128KB/s, Max Upload Speed =128KB/s, Chunk size=32KB Average Download Speed (KB/s) Algorithms/Key Size (bit) RSA120,85120,41119,33118,65 DSA120,75120,84120,72120,68 ECDSA(spec160r1/spec224r1)120,89120,75 No Signature121,43

4.3 Data Analysis Max Download Speed =10MB, 150MB File Size, Chunk size=32KB Max Download Speed =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. Conclusion P2P Networks Millions of Users Secure, Efficient, Energy saving… VoIP BitTorrent TCP http Services

Thank You!