Lecture notes on Wireless and Mobile computing

security considerations in mobile and wireless computing
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Published Date:11-07-2017
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Lectures 6: Security for Mobile and Wireless Computing Ing-Ray Chen CS 6204 Mobile Computing Virginia Tech Courtesy of G.G. Richard III for providing some of the slides 1 Protect what? • Integrity – System: performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system. – Data: Should be possible for a receiver to verify that data has not been modified; an intruder should not be able to substitute fake data • Confidentiality – Only intended recipient(s) should be able to read data • Non-repudiation – Sender should not be able to falsely deny sending data. • Availability (Denial of Service, Distributed DoS) – A third party with no access should not be able to block legitimate parties from using a resource. 2 Security: Before/During/After Attack •Prevention (before) – Authentication, authorization, accounting •Detection (during) – Intrusion Detection • Host/network • Signature/Anomaly behavior •Reaction (after) – Digital Forensics • Evidence preservation • Who? What? When? From where? • Sources (files, logs, timestamp info, ISP records, …) – Attack Assessment, Damage Assessment, Data Recovery 3 Before • Prevention – Authentication: “Are they who they claim to be?” “The act of verifying a claimed identity, in the form of a pre- existing label from a mutually known name space, as the originator of a message (message authentication) or as the end- point of a channel (entity authentication).” – Authorization: “Do they have permission to do it?” “The act of determining if a particular right, such as access to some resource, can be granted to the presenter of a particular credential.” – Accounting: a log or history of what happened “The collection of resource consumption data for the purposes of capacity and trend analysis, cost allocation, auditing, and billing. Accounting management requires that resource consumption be measured, rated, assigned, and communicated between appropriate parties.” 4 Wireless Risks • Wireless – all of the above concerns plus an increased risk of eavesdropping (and transmitting). – No need to tap or plug into the network. Only need to be “nearby.” – Depending on the wireless technology, nearby can be line-of-sight, same room, outside a building, within a few miles • Greatly increases threats to confidentiality, integrity, authentication, non-repudiation 5 Wireless Risks (2) These risks can allow adversaries to: • Perform data snooping • Hijack sessions (e.g., Man-in-the-middle) • Commit fraud and identity theft (e.g., gathering an individual's personal information from RF-enabled cards carried on a person in their access control) 6 Risks: Resource Depletion • Hardware limitations, such as low network bandwidth and limited battery power, also increases denial-of-service risk: – Resource depletion/exhaustion attacks “want a business card?” “want a business card?” “want a business card?” “want a business card?” “want a business card?” “want a business card?” “want a business card?” “want a business card?” 7 Protections • Make it harder to intercept transmissions at the intruder’s physical layer – Use low power, limit reception/interception range. – Use a technique like frequency hopping • But, generally want anyone to be able to join in and use the network. • Frequency hopping is actually used to increase number of users, not for protection. 8 Protections • Encryption: “they” can’t decode data, so they can’t use what they do steal • Digital signatures: prevent forging or modifying data 9 Encryption P C ABC DEF ?T encryption GHI = function key cx • Public key: • Symmetric key: C = E (P), pub C = E (P), k P = D (C), also priv P = D (C) C’ = E (P), k priv P = D (C’) 10 pubBlock vs. Stream Cipher Block cipher: accumulates a group of key plaintext and then operates on it at once (e.g., 64 bits at a time) and produces an encrypted block of equal size. e.g., DES, AES, RSA E(block) block block Plain text cipher text stream key Pseudo-random stream generator Stream cipher: operate on plaintext a single 11 bit/byte at a time. e.g., RC4 used in WEP Simple examples – XOR: Plaintext Key Ciphertext • 1111 0000 XOR 1010 1010 = 0101 1010 • 0101 1010 XOR 1010 1010 = 1111 0000 ( Note that this is really a single sample from a key-stream.) – Rotation (trivial cipher): • ROT1: “HAL”  “IBM” 12 Message Digests and Hashes P H(P) Message Digest ABC 3C 00 3C FF 01 One-way FE CB E6 A4 22 DEF 19 5D 8B EE … hash GHI • A cryptographically secure one-way hash function produces a short sequence of bytes (e.g., 128 or 160 bits) based on the input. • e.g., MD4, MD5, SHA 13 Hash Space . . . 1,000,201,548,007 1,000,201,548,008 1,000,201,548,009 . . . A Long Time ago We the ABC in a galaxy people DEF far, far, … GHI away • Cryptographically secure: A single bit change in source changes ½ the bits in the hash. • Small changes in the hash come from very different sources. • Computationally infeasible to find matching source from hash. 14 Message Authentication Code (MAC) P + MAC key P ABC DEF H(P, key) ABC • H(P key) GHI DEF or P X. / n +p 1c M ex xq P MAC GHI • Encrypted H(P) Rk os qp … • For authenticity without secrecy: attach the MAC to the message • MAC is a one-way hash function plus a secret key – Hash the concatenation of the message and key, or – Encrypt the hash of the message with the key 15 Message Overhead of Encryption • Public key: send the message one by one using the receiver’s public key – Message overhead is n M, where • n: number of recipients • M: message length • Hybrid (PGP): encrypt shared session key using public key encryption one by one and then broadcast the encrypted message with the shared key – Message overhead is nK + M, where • K: key length of a shared session key • If M k, message overhead is greatly reduced 16 Costs of Protections • Encryption overhead (more tradeoffs) – Poor performance – CPU load – Power consumption – Reduced battery life – Increased data size  increased transmission time 17 Cost of Protections • Public Key Infrastructure (PKI) • Certificates – Certificate revocation or expiration rd – Trusted 3 party • Shared secret key (and risk) vs. public key • Key management – Key setup – Key exchange • Individual vs. group keys (overhead) 18 Misc. Attacks Counterattack methods: • Man-in-the-middle attacks – Use authentication • Replay attacks – Use sequence number or one-time unique number (called nounce) that will not be honored the second time • Traffic analysis – Use encrypted communication (e.g., IPsec) 19 IEEE 802 Standards – 802.11 – Wireless LAN • 802.11 – IEEE Standard, • 802.11 – “basic” wireless 1997. • 802.11a - 5GHz, 54Mb • 802 LAN/MAN Standard • 802.11b – 2.4GHz, 11Mb Committee • 802.11e – QoS – 802.1d – MAC bridging • 802.11f – AP interop standard • 802.11g – faster 802.11b, starting at 20Mbps – 802.1x – Port-based Network • 802.11h – transmit power Access Control control for 802.11a (Europe) – 802.2 – Logical Link Control • 802.11i – better security – 802.3 – Ethernet • 802.11j – Japanese 802.11 • 802.3z – 100BaseT Fast • 802.11n – 600Mb MIMO Ethernet • 802.11p – automotive apps – 802.5 – Token Ring – 802.15.1 Bluetooth – 802.15.4 Low-rate (low power) (ZigBee on top of 802.15.4) – 802.16 Wireless Metropolitan 20 Area Network (WMAN)

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