Anonymity in Bitcoin. Presenter: Muhammad Anas Imtiaz

Transcription

1 Anonymity in Bitcoin Presenter: Muhammad Anas Imtiaz Based on: An analysis of anonymity in the Bitcoin System [1], and Tracking digital footprints: anonymity within the bitcoin system [4]

2 Introduction Decentralized, P2P cryptocurrency introduced by Nakamoto [2] in 2008 First transaction in January, 2009 All-time high market cap of $300+ billion [3] Transactions published in a public ledger Nodes maintain copy of ledger to validate transactions

3 Introduction Concerns regarding untraceability US: FBI [5], senators Europe: Der Bundesverband Digitale Wirtschaft Tax evasions, money laundering, illegal transactions General unawareness regarding anonymity throughout Bitcoin community Is it really anonymous?

4 Transaction Transfer of Bitcoin from a source account to a destination account An account is a public/private-keypair Signed with private key of sender Destination is the public key of recipient

5 Transaction com/uploads/images/ ad1f3d1790b9f1f7764 fbc72f2337b6c44cd5a dfba10324a9a8a65e5 b6b09125.png An input may be claimed only once Multiple inputs, multiple outputs Sum of the values of inputs sum of the values of outputs

6 Block A set of transactions Created by participants of the Bitcoin network

7 Blockchain A collection of blocks ordered chronologically Each block is linked to the previous block Public ledger Each node has its own copy

8 Features of Interest Public availability of the ledger Transactions with multiple inputs and multiple outputs Payer and payee identified through public-keys Multiple public-keys

9 Features of Interest Public availability of the ledger Transactions with multiple inputs and multiple outputs Payer and payee identified through public-keys Multiple public-keys Allow to create two network structures The transaction network The user network

10 Transaction Network Flow of Bitcoins between transactions Vertex: transaction Directed edge: output of source transaction to input of target transaction; value of transaction

11 Transaction Network

12 User Network Flow of Bitcoins between users Vertex: user Directed edge: input-output pair of a single transaction; value of transaction

13 User Network Flow of Bitcoins between users Vertex: user single public-key Directed edge: input-output pair of a single transaction between users public-keys; value of transaction

14 User Network

15 Features of Interest Public availability of the ledger Transactions with multiple inputs and multiple outputs Payer and payee identified through public-keys Multiple public-keys Allow to create two network structures The transaction network The user network

16 User Network Some linking is still unavoidable with multi-input transactions, which necessarily reveal that their inputs were owned by the same owner. The risk is that if the owner of a key is revealed, linking could reveal other transactions that belonged to the same owner [2]

17 User Network

18 Analysis De-anonymize users No user directory Off-Network information On-line stores, exchanges etc. Voluntary disclosure

19 Analysis More information can be derived

20 Analysis

21 Case Study

22 Case Study

23 Case Study

24 Further Analysis Is this really helpful for law enforcement agencies? Do exchanges require user information?

25 Further Analysis Round 1 Tor, fake information (name, birth date, ) Submitted as real to exchanges

26 Further Analysis Round 2 Ninja Cloak, fake information (name, birth date, ), correct information (street names, numbers) Submitted as real to exchanges

27 Possible Workarounds (?) Use a mixing service Requires trust Mixing services may store information Don t store all Bitcoin in one location

28 Interesting Links Bitcoin theft: Paper thrashing: and Patching Bitcoin: BitcoinWiki on Anonymity:

29

30 References [1] Reid, Fergal, and Martin Harrigan. "An analysis of anonymity in the bitcoin system." Privacy, Security, Risk and Trust (PASSAT) and 2011 IEEE Third Inernational Conference on Social Computing (SocialCom), 2011 IEEE Third International Conference on. IEEE, [2] Satoshi Nakamoto. Bitcoin: A peer-to-peer electronic cash system. [3] [4] Reynolds, Perri, and Angela SM Irwin. "Tracking digital footprints: anonymity within the bitcoin system." Journal of Money Laundering Control 20.2 (2017): [5] Bitcoin FBI.