Proving the Impossible with Alibi Protocols
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1 Proving the Impossible with Alibi Protocols Dave Levin Victoria Lai, Cristian Lumezanu, Neil Spring, Bobby Bhattacharjee, Bo Han, John Douceur, Jacob Lorch, Thomas Moscibroda
2 Uncooperative behavior Cooperation Anything and everything for the good of the network Selfishness Malice Gain at the potential expense of others Break the system for notoriety or profit
3 Uncooperative behavior Cooperation Routing: ARPANet s global policy Selfishness Malice Routing: BGP Local pref Routing: Prefix hijacking
4 Uncooperative behavior Cooperation Routing: Transport: ARPANet s global policy TCP congestion control Selfishness Malice Routing: BGP Local pref Routing: Prefix hijacking Transport: TCP Opt-Ack Transport: Mitnick attack
5 Uncooperative behavior Cooperation Routing: Transport: ARPANet s global policy TCP congestion control Selfishness Malice Routing: BGP Local pref Routing: Prefix hijacking Transport: TCP Opt-Ack Transport: Mitnick attack
6 Censorship via DNS injection Censoring AS [Anonymous authors, ACM CCR 2012]
7 Censorship via DNS injection Censoring AS [Anonymous authors, ACM CCR 2012]
8 Censorship via DNS injection lemon IP Censoring AS [Anonymous authors, ACM CCR 2012]
9 Censorship via DNS injection Censor-free ASes lemon IP Censoring AS [Anonymous authors, ACM CCR 2012]
10 Censorship via DNS injection Censor-free ASes lemon IP Censoring AS [Anonymous authors, ACM CCR 2012]
11 Censorship via DNS injection Censor-free ASes lemon IP lemon IP Censoring AS [Anonymous authors, ACM CCR 2012]
12 Censorship via DNS injection Censor-free ASes lemon IP Censoring AS [Anonymous authors, ACM CCR 2012]
13 Building secure decentralized systems Make malfeasance impossible Make malfeasance unprofitable Allow no progress if incorrect DNSSEC, Secure BGP,... Heavyweight Remove the incentive to be incorrect Assumptions not always aligned Make malfeasance detectable Allow incorrect progress Prove that nothing bad happened Ideally, lighter-weight
14 Building secure decentralized systems Make malfeasance impossible Make malfeasance unprofitable Allow no progress if incorrect DNSSEC, Secure BGP,... Heavyweight Remove the incentive to be incorrect Assumptions not always aligned Make malfeasance detectable Allow incorrect progress Prove that nothing bad happened Ideally, lighter-weight
15 Building secure decentralized systems Make malfeasance impossible Make malfeasance unprofitable Allow no progress if incorrect DNSSEC, Secure BGP,... Heavyweight Remove the incentive to be incorrect Assumptions not always aligned Make malfeasance detectable Allow incorrect progress Prove that nothing bad happened Ideally, lighter-weight
16 Building secure decentralized systems Make malfeasance impossible Make malfeasance unprofitable Allow no progress if incorrect DNSSEC, Secure BGP,... Heavyweight Remove the incentive to be incorrect Assumptions not always aligned Make malfeasance detectable Allow incorrect progress Prove that nothing bad happened Ideally, lighter-weight But how do you prove something did not happen?
17 One option: Monitor everything Watch everything that everyone does Watch those who watch everything that everyone does Simulate the system based on its inputs and outputs If it didn t happen in simulation, and if the monitoring was done well, then it probably didn t happen
18 Proving something didn t happen Provide a (small) proof that event A happened If events A and B are mutually exclusive Then B could not have happened
19 Proving something didn t happen Provide a (small) proof that event A happened If events A and B are mutually exclusive Then B could not have happened A serves as an alibi
20 Alibi protocols TrInc: Small, trusted h/w Fighting equivocation with trusted counters NSDI 09 Alibi routing Provably avoiding regions of the network Ongoing
21 Alibi protocols TrInc: Small, trusted h/w Fighting equivocation with trusted counters NSDI 09 Alibi routing Provably avoiding regions of the network Ongoing
22 Trust in distributed systems Selfish Participants Malicious Participants
23 Trust in distributed systems Selfish Participants Malicious Participants Powerful tool: Equivocation A participant equivocates by sending conflicting messages to others
24 Equivocation is versatile and powerful Byz. Generals
25 Equivocation is versatile and powerful Byz. Generals Advance Retreat
26 Equivocation is versatile and powerful Byz. Generals Voting BitTorrent Advance Counted your vote I have piece 5 Retreat Tally w/o s vote I don t have piece 5 Leader election Trusted logs sobgp Digital cash Online games Version control Auctions DHTs
27 Equivocation is versatile and powerful Byz. Generals Advance f malicious users If completely untrusted, 3f+1 users needed for consensus [Lamport et al., 1982] Retreat
28 Equivocation is versatile and powerful Byz. Generals Advance Retreat f malicious users If completely untrusted, 3f+1 users needed for consensus [Lamport et al., 1982] If users cannot equivocate, only 2f+1 users are needed [Chun et al., 2007]
29 Enter Trusted Hardware Equivocation can be rendered impossible with trusted hardware New design space All participants have a trusted component
30 Enter Trusted Hardware Equivocation can be rendered impossible with trusted hardware New design space All participants have a trusted component
31 Enter Trusted Hardware Equivocation can be rendered impossible with trusted hardware New design space All participants have a trusted component
32 Enter Trusted Hardware Equivocation can be rendered impossible with trusted hardware New design space All participants have a trusted component To be practical, the hardware must be small Ubiquity via low cost Tamper-resilient Easier to verify a small TCB
33 Motivating question What is the minimal abstraction needed to make equivocation impossible?
34 Motivating question What is the minimal abstraction needed to make equivocation impossible? A counter and a key are enough
35 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations 34 K
36 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) 34 K
37 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) 34 K
38 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) K
39 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K
40 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K Alibi: Nothing was bound to 35
41 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K Alibi: Nothing was bound to K
42 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K Alibi: Nothing was bound to 35 Attest(36, non) 36 K
43 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K Alibi: Nothing was bound to 35 Attest(36, non) 36 K
44 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K Alibi: Nothing was bound to 35 Attest(36, non) 36 < 36, 36, non >K K
45 TrInc: Trusted Incrementer 1. Monotonically increasing counter 2. Key for signing attestations Attest(36, data) < 34, 36, data >K K Alibi: Nothing was bound to 35 Attest(36, non) 36 < 36, 36, non >K K Status attestation
46 What can TrInc do? Trusted append-only logs Prevent under-reporting in BitTorrent Reduces communication in PeerReview BFT with fewer nodes and messages Ensure fresh data in DHTs Prevent Sybil attacks
47 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored
48 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log 10 Lookup(sequence num): No equivocating on what is or is not stored
49 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log 10 Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > Untrusted storage
50 Implementing a trusted log in TrInc append Append(data): Bind new data to the end of the log 10 Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > Untrusted storage
51 Implementing a trusted log in TrInc attest(11,, ) Append(data): Bind new data to the end of the log 10 Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > Untrusted storage
52 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log 10 Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > Untrusted storage
53 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > Untrusted storage
54 Implementing a trusted log in TrInc < 10,11, > Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > Untrusted storage
55 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > < 10,11, > Untrusted storage
56 Implementing a trusted log in TrInc lookup 10 Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > < 10,11, > Untrusted storage
57 Implementing a trusted log in TrInc lookup 10 Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > < 10,11, > Untrusted storage
58 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > < 10,11, > Untrusted storage
59 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > < 9,10, > < 10,11, > Untrusted storage
60 Implementing a trusted log in TrInc Append(data): Bind new data to the end of the log Lookup(sequence num): No equivocating on what is or is not stored < 3,8, > < 8,9, > < 9,10, > < 10,11, > < 9,10, > Fast lookups Few hardware accesses Untrusted storage
61 TrInc Summary Equivocation is versatile and powerful A small amount of trust can secure a large system TrInc is Minimal? A counter and a key Versatile Applies to a wide range of systems Practical Uses the familiar components (in unfamiliar ways)
62 Alibi protocols TrInc: Small, trusted h/w Fighting equivocation with trusted counters NSDI 09 Alibi routing Provably avoiding regions of the network Ongoing
63 Alibi protocols TrInc: Small, trusted h/w Fighting equivocation with trusted counters NSDI 09 Alibi routing Provably avoiding regions of the network Ongoing
64 Avoiding censors Censor-free ASes lemon IP Censoring AS
65 Avoiding censors Censor-free ASes lemon IP Censoring AS
66 Avoiding censors Censor-free ASes but avoid lemon IP Censoring AS
67 Alibi routing
68 Alibi routing
69 Alibi routing Solicit participation from a relay
70 Alibi routing A signature proves the relay forwarded it Solicit participation from a relay
71 Alibi routing A signature proves the relay forwarded it Solicit participation from a relay
72 Alibi routing
73 Alibi routing
74 Alibi routing The triangle inequality mostly holds in the Internet
75 Alibi routing The triangle inequality mostly holds in the Internet Going through the boycotted region would increase latency
76 Alibi routing The farther away the relay, the greater the latency increase. The triangle inequality mostly holds in the Internet Going through the boycotted region would increase latency
77 Finding relays Embed end hosts and regions into a coordinate space Query regions of the space that are far from the avoidee
78 Finding relays Embed end hosts and regions into a coordinate space Query regions of the space that are far from the avoidee
79 Finding relays Embed end hosts and regions into a coordinate space Query regions of the space that are far from the avoidee
80 Finding relays Embed end hosts and regions into a coordinate space Query regions of the space that are far from the avoidee
81 Finding relays Embed end hosts and regions into a coordinate space Query regions of the space that are far from the avoidee
82 Can countries avoid one another? NorthAmerica MiddleEast Europe SouthAmerica Asia 0.6 CDF Number of reachable destinations
83 Can countries avoid one another? Ideal NorthAmerica MiddleEast Europe SouthAmerica Asia 0.6 CDF Number of reachable destinations
84 Can countries avoid one another? NorthAmerica MiddleEast Europe SouthAmerica Asia 0.6 CDF Number of reachable destinations
85 Can countries avoid one another? NorthAmerica MiddleEast Europe SouthAmerica Asia CDF Multiple relays may be necessary Number of reachable destinations
86 Can countries avoid one another? NorthAmerica MiddleEast Europe SouthAmerica Asia CDF Multiple relays may be necessary A few tens of Number of reachable destinations milliseconds often suffices (not shown)
87 Alibi routing is not a panacea Packets can always be copied Provides a small but useful signal to systems: This packet didn t go somewhere bad Or else it might have Systems must decide how to react to that signal Drop the connection? Initiate stronger end-to-end protection?
88 Proving the impossible with alibis Global systems require interactions among self-interested parties Alibi protocols prove something untoward did not happen Without having to prove everything that did An attractive alternative to traditional accountability systems Lightweight Easy to deploy Easy to incorporate with existing systems
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