Prefix-Preserving IP Address Anonymization: Measurement-based Security Evaluation and a New Cryptography-based Scheme Jun Xu, Jinliang Fan, Mostafa Ammar, Sue Moon College of Computing Sprint ATL Georgia Tech modified & presented by Zihui Ge

1 Overview  Motivation  IP address anonymization prefix-preserving  Prefix-preserving anonymization  canonical form  TCPdpriv  cryptography-based scheme  Attacks  models, analysis, evaluation

1 Motivation  Traces collected, to share or not to share?  client personal privacy?  commercial confidentiality?  IP address anonymization  →  one to one mapping, consistent  Prefix relationships among IP addresses?  important: routing performance, clustering of end-systems  Prefix-preserving anonymization  →  →  preserve prefix correlation among addresses

1 IP Address Anonymization  Basic anonymization a: original 4-byte IP address a =a 1 a 2 … a 32 a’: anonymized IP addressa’=a’ 1 a’ 2 …a’ 32 F: 1-to-1 mapping functiona’=F(a)  Prefix preserving anonymization if a, b share k-bit prefix a 1 =b 1,a 2 =b 2, …, a k =b k, a k+1 =b k+1 then a’=F(a), b’=F(b) share k-bit prefix a’ 1 =b’ 1,a’ 2 =b’ 2, …, a’ k =b’ k, a’ k+1 =b’ k+1

1 Canonical Form  Canonical construction of F using a series of f i a’ i = a i  f i-1 (a 1, a 2, …, a i-1 ) f 0 is a constant  F is a prefix-preserving anonymization function  A prefix-preserving anonymization function necessarily takes this form  Different schemes use different f i  Visualized as a tree

1 Visualization : Address Space

1 Visualization: Original Address Tree

1 Visualization: Anonymization Function FlipLeaf Node f 0 ()= f 1 (0)=1 f 1 (1)=0 f 2 (0,0)=0

Visualization: Anonymized Address Tree

1 TCPdpriv a 1 a 2 …a k a k+1 a K+2 …a n rand(a 1 a 2 …a k a k+1 …a n ) a 1 a 2 …a k a k+1 b k+2 …b n a’ 1 a’ 2 …a’ k a’ k+1 …a’ n a’ 1 a’ 2 …a’ k a’ k+1 a’ 1 a’ 2 …a’ k a’ k+1 b’ k+2 …b’ n  Sequentially scan IP address  look up prefix in “history” table  randomly choose suffix  concatenate prefix,suffix; update “history” table rand(b k+2 …b n )

1 TCPdpriv  Sequentially scan IP address  look up prefix in “history” table  randomly choose suffix  concatenate prefix,suffix; update “history” table  Mapping is trace-dependent  Need to maintain a table to track previous mappings  table size grow over time  look up cost increase over time  Unable to process in parallel

1 New Crytography-Based Algorithm  deterministic f i function  trace-independent  What PRF to use?  Practical bock ciphers, e.g., AES, can be modeled as PRP L: least significant bit R: pseudo-random function P: secret padding K: secret key f i (a 1, a 2, …, a i-1 ) := L(R(P(a 1 a 2 …a i-1 ), K))

1 Attacks on Anonymization Schemes  Cryptographic attacks  scheme specific  vulnerability comes from the specific construction of f i  TCPdpriv: not susceptible  our scheme: provable secure  Semantic attacks  common to all schemes  vulnerability comes from the canonical construction of F  effectiveness should be measured

1 Evaluation of Semantic Attacks  Metrics to measure effect of attacks  Virtual (but theoretically interesting) attacks  good measure of the resistance of a specific trace to semantic attacks in general  good relative reference points for measuring the effectiveness of practical attacks.  Practical attacks

1 Metrics to Measure Effect of Attacks  Measure of attack severity:  U: # of unknown uncompressed bits  C: # of unknown compressed bits  K i : # of addresses with exactly i known most significant bit

1 If an address is compromised … C=9, U=18, K 1 =4, K 2 =2, K 3 =2, K 4 =1000?0010 1??? 000? 01?? 1???

1 Evaluation on Real Traces  Measure the resistance of a specific trace to semantic attacks in general  Effect of compromising random address  Effect of compromising greedily-generated address

1 Effect of Compromising Random Addresses

1 Practical Attacks  Frequency Analysis  DNS Server Address Tracing  Others

1 Conclusions  Canonical form of constructing prefix- preserving anonymization function  New cryptography-based scheme  Framework of measuring the resistance of traces and the effectiveness of attacks  Implementation