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Introduction Issues Design Goals Classifications TCP Over Ad Hoc Wireless Networks Other Transport Layer Protocols. Security in Ad Hoc Wireless Networks Network Security Requirements Issues and challenges in security Network security attacks Key Management Secure Routing.
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Introduction • Issues • Design Goals • Classifications • TCP Over Ad Hoc Wireless Networks • Other Transport Layer Protocols • Security in Ad Hoc Wireless Networks • Network Security Requirements • Issues and challenges in security • Network security attacks • Key Management • Secure Routing Chapter 9: Transport Layer and Security Protocols for Ad Hoc Wireless Networks
Introduction • The objectives of a transport layer protocol include setting up of: • End-to-end connection • End-to-end delivery of data packets • Flow control • Congestion control • Transport layer protocols • User datagram protocol (UDP): unreliable and connection-less transport layer protocols • Transmission control protocol (TCP): reliable, byte-stream-based, and connection-oriented transport layer protocols • These traditional wired transport layer protocols are not suitable for ad hoc wireless networks.
Issues • Issues while designing a transport layer protocol for ad hoc wireless networks: • Induced traffic refers to the traffic at any given link due to the relay traffic through neighboring links. • Induced throughput unfairness refers to the throughput unfairness at the transport layer due to the throughput/delay unfairness existing at the lower layers such as the network and MAC layers. • Separation of congestion control, reliability, and flow control could improve the performance of the transport layer. • Power and bandwidth constraints affects the performance of a transport layer protocol. • Misinterpretation of congestion occurs in ad hoc wireless networks. • Completely decoupled transport layer needs to adapt to the changing network environment. • Dynamic topology affects the performance of a transport layer.
Design Goal • The protocol should maximize the throughput per connection. • It should provide throughout fairness across contending flows. • It should minimize connection setup and connection maintenance overheads. • The protocol should have mechanisms for congestion control and flow control in the network. • It should be able to provide both reliable and unreliable connections. • The protocol should be able to adapt to the dynamics of the network. • One of the important resources must be used efficiently. • The protocol should be aware of resource constraints. • The protocol should make use of information from the lower layer. • It should have a well-defined cross-layer interaction framework. • The protocol should maintain end-to-end semantics.
Classification of Transport Layer Solutions Transport Layer Solutions for Ad Hoc Wireless Networks Other transport layer approach TCP over ad hoc wireless networks ACTP ATP Split Approach End-to-end approach TCP-ELFN Split-TCP TCP-F TCP-Bus ATCP
TCP over Ad Hoc Wireless Networks • TCP taking 90% of the traffic is predominant in the Internet. • This chapter focuses on TCP extension in ad hoc wireless networks. • Transport protocol should be independent of the network layer technology, e.g., no matter fiber or radio is used • But TCP is optimized for wired network Congestion control • TCP assumes timeout is due to congestion • Wireless links are not reliable, packet loss may be as high as 20% • In wired network, packet loss is due to congestion slow down • In wireless network, due to wireless links try harder
Why does TCP not perform well in Ad Hoc Wireless Networks • Misinterpretation of packet loss • Frequent path breaks • Effect of path length • Misinterpretation of congestion window • Asymmetric link behavior • Uni-directional path: TCP ACK requires RTS-CTS-Data-ACK exchange • Multipath routing • Network partitioning and remerging • The use of sliding-window-based transmission
TCP Over Ad Hoc Wireless Network • Feedback-based TCP (TCP Feedback – TCP-F) • Requires the support of a reliable link layer and a routing protocol that can provide feedback to the TCP sender about the path breaks. • The routing protocol is expected to repair the broken path within a reasonable time period. • Advantages: Simple, permits the TCP congestion control mechanism to respond to congestion • Disadvantages: • If a route to the sender is not available at the failure point (FP), then additional control packets may need to be generated for routing the route failure notification (RFN) packet. • Requires modification to the existing TCP. • The congestion window after a new route is obtained may not reflect the achievable transmission rate acceptable to the network and the TCP-F receiver.
TCP Over Ad Hoc Wireless Network • TCP with explicit link failure notification (TCP-ELFN) • Handle explicit link failure notification • Use TCP probe packets for detecting the route reestablishment. • The ELFN is originated by the node detecting a path break upon detection of a link failure to the TCP sender. • Advantages: • improves the TCP performance by decoupling the path break information from the congestion information by the use of ELFN. • Less dependent on the routing protocol and requires only link failure notification • Disadvantages • When the network is partitioned, the path failure may last longer • The congestion window after a new route is obtained may not reflect the achievable transmission rate acceptable to the network and TCP receiver.
TCP Over Ad Hoc Wireless Network • TCP with buffering capability and sequence information (TCP-BuS) • Use feedback information from an intermediate node on detection of a path break. • Use localized query (LQ) and REPLY to find a partial path • Upon detection of a path break, an upstream intermediate node originates an explicit route disconnection notification (ERDN) message. • Advantages • Performance improvement and avoidance of fast retransmission • Use on-demand routing protocol • Disadvantages • Increased dependency on the routing protocol and the buffering at the intermediate nodes • The failure of intermediate nodes may lead to loss of packets. • The dependency of TCP-BuS on the routing protocol many degrade its performance.
TCP Over Ad Hoc Wireless Network • Ad Hoc TCP (ATCP) • uses a network layer feedback mechanism to make the TCP sender aware of the status of the network path • Based on the feedback information received from the intermediate nodes, the TCP sender changes its state to the persist state, congestion control state, or the retransmit state. • When an intermediate node finds that the network is partitioned, then the TCP sender state is changed to the persist state. • The ATCP layer makes use of the explicit congestion notification (ECN) for maintenance for the states. • Advantages • Maintain the end-to-end semantics of TCP • Compatible with traditional TCP • Provides a feasible and efficient solution to improve throughput of TCP • Disadvantages • The dependency on the network layer protocol to detect the route changes and partitions • The addition of a thin ATCP layer to the TCP/IP protocol changes the interface functions currently being used.
TCP Over Ad Hoc Wireless Network • Split-TCP • provides a unique solution to the channel fairness problem by splitting the transport layer objectives into congestion control and end-to-end reliability. • Splits a long TCP connection into a set of short concatenated TCP connections with a number of selected intermediate nodes as terminating points of these short connections. • Advantages • Improved throughput • Improved throughput fairness • Lessened impact of mobility • Disadvantages • It requires modifications to TCP protocol. • The end-to-end connection handling of traditional TCP is violated. • The failure of proxy nodes can lead to throughput degradation.
Other Transport Layer Protocols • Application controlled transport protocol (ACTP) • A light-weight transport layer protocol and not an extension to TCP. • ACTP assigns the responsibility of ensuring reliability to the application layer. • ACTP stands in between TCP and UDP where TCP experiences low performance with high reliability and UDP provides better performance with high packet loss in ad hoc wireless networks. • Advantages • Provides the freedom of choosing the required reliability level to the application layer. • Scalable for large networks • There is no congestion window • Disadvantages • It is not compatible with TCP. • Could lead to heavy congestion
Other Transport Layer Protocols • Ad hoc transport protocol (ATP) • specifically designed for ad hoc wireless networks and is not a variant of TCP and differ from TCP in the following ways: • Coordination among multiple layers • Rate based transmissions • Decoupling congestion control and reliability • Assisted congestion control • ATP uses information from lower layers for • Estimation of the initial transmission rate • Detection, avoidance, and control of congestion • Detection of path breaks • Advantages: improved performance, decoupling of the congestion control and reliability mechanisms, and avoidance of congestion window fluctuations • Disadvantages • The lack of interoperability with TCP • Fine-grained per-flow timer may cause the scalable problem
Security in Ad Hoc Wireless Networks • A security protocol should meet following requirements • Data confidentiality/secrecy is concerned with ensuring that data is not exposed to unauthorized users. • Data integrity means that unauthorized users should not be able to modify any data without the owner's permission. • System availability means that nobody can disturb the system to have it unusable. • Authentication is concerned with verifying the identity of a user. • Non-repudiation means that the sender cannot deny having sent a message and the recipient cannot deny have received the message.
Security in Ad Hoc Wireless Networks • Issues and challenges in security provisioning • Shared broadcast radio channel: The radio channel in ad hoc wireless networks is broadcast and is shared by all nodes in the network. • Insecure operational environment: The operating environments where ad hoc wireless networks are used may not always be secure. For example, battlefields. • Lack of central authority: There is no central monitor in ad hoc wireless networks. • Lack of association: A node can join and leave the network at any point. • Limited resource availability: Resources such as bandwidth, battery power, and computational power are scarce. • Physical vulnerability: Nodes in these networks are usually compact and hand-held in nature.
Need for Security • Some people who cause security problems and why.
Security Threats • Four types of security threats: • Interception refers to the situation that an unauthorized party has gained access to a service or data. • Interruption refers to the situation in which services or data become unavailable, unusable, or destroyed. • Modifications involve unauthorized changing of data or tampering with a service. • Fabrication refers to the situation in which additional data or activity are generated that would normally not exist.
Network Security Attacks • Network Layer Attacks • Wormhole attack: an attacker receives packets at one location in the network and tunnels them to another location in the network. • Blackhole attack: A malicious node could divert the packets. • Byzantine attack: A compromised intermediate node could create routing loops. • Information disclosure: A compromised node may leak confidential infomraiton to unauthorized nodes in the network. • Resource consumption attack: A malicious node tries to consume/waste away resources of other nodes present in the network. • Routing attacks • Routing table overflow: An adversary node advertises routes to non-existent nodes. • Routing table poisoning: The compromised nodes send fictitious routing updates. • Packet replication: An adversary node replicates stale packets. • Route cache poisoning: Each node maintains a route cache that can be poisoned by a adversary node. • Rushing attack: On-demand routing protocols that use duplicate suppression during the route discovery process are vulnerable to this attack.
Network Security Attacks • Transport Layer Attacks • Session hijacking: An adversary takes control over a session between two nodes. • Application Layer Attacks • Repudiation: Repudiation refers to the denial or attempted denial by a node involved in a communication. • Other Attacks • Multi-layer attacks could occur in any layer of the network protocol stack. • Denial of service: An adversary attempts to prevent authorized users from accessing the service. • Jamming: Transmitting signals on the frequency of senders and receivers to hinder the communication. • SYN flooding: An adversary send a large number of SYN packets to a victim node. • Distributed DoS attack: Several adversaries attack a service at the same time. • Impersonation: An adversary pretends to be other node. • Device tampering: Mobile devices get damaged or stolen easily.
Network Security Attacks Security Attacks Active Attacks Passive Attacks Snooping MAC Layer Attacks Network Layer Attacks Other attacks Transport Layer Attacks Application Layer Attacks Wormhole attack Session hijacking Jamming Repudiation DoS Impersonation Blackhole attack Manipulation of network traffic Byzantine attack Information disclosure Device tampering Resource consumption attack Routing attacks
Key Management • Cryptography is one of the most common and reliable means to ensure security. • The purpose of cryptography is to take a message or a file, called the plaintext (P), and encrypt it into the ciphertext (C) in such a way that only authorized people know how to convert it back to the plaintext. • The secrecy depends on parameters to the algorithms called keys. • The four main goals of cryptography are confidentiality, integrity, authentication, and non-repudiation. • Usually, the encryption method E is made public, but let the encryption as a whole be parameterized by means of a key k (same for decryption). • Three types of intruders: • Passive intruder only listens to messages. • Active intruder can alter messages. • Active intruder can insert messages.
Cryptography Intruders and eavesdroppers in communication.
Cryptography • There are two major kinds of cryptographic algorithms: • Symmetric (secret-key) system: Use a single key to (1) encrypt the plaintext and (2) decrypt the ciphertext. Requires that sender and receiver share the secret key. • Asymmetric (public-key) system: Use different keys for encryption and decryption, of which one is private, and the other public. • Hashing system: Only encrypt data and produce a fixedlength digest. There is no decryption; only comparison is possible.
Security Cryptography Security algorithms services Secret Public Message Privacy Authentication Message key key digest integrity (e.g., DES) (e.g., RSA) (e.g., MD5) Cryptography Functions • Cryptography functions • Secret key (symmetric cryptography, e.g., DES) • Public key (asymmetric cryptography, e.g., RSA) • Hashing (one-way function - message digest, e.g., MD5)Security services • Security services • Privacy (Secrecy): preventing unauthorized release of information • Authentication: verifying identity of the remote participant • Integrity: making sure message has not been altered
Symmetric Cryptosystems • Substitute Cipher: each letter or group of letter is replaced by another letter or group of letters • Caesar cipher: rotate the letter (a D, b E, c F, z C). • Example: attack DWWDFN • Monoalphabetic substitution • Each letter replaced by different letter Plaintext: ABCDEFGHIJKLMNOPQRSTUVWXYZ Ciphertext: QWERTYUIOPASDFGHJKLZXCVBNM • Disadvantage: It does not smooth out frequencies in the cipher text. • Polyalphabatic cipher – use multiple cipher alphabets.
Secret-Key Cryptography • Transposition cipher: reorder the letters, but don't disguise them. • Select a key MEGABUCK 7 4 5 1 2 8 3 6 p l e a s e t r a n s f e r o n e h u n d r e d afnsedtoelnhesurndpaeerr Plain text cipher text
Transposition Ciphers • A transposition cipher.
One-Time Pads The use of a one-time pad for encryption and the possibility of getting any possible plaintext from the ciphertext by the use of some other pad.
Symmetric Cryptosystems: DES • Data Data Encryption Standard (DES) was developed by IBM and adopted as a US national standard in 1977. • The encryption function maps a 64-bit plaintext input into a 64-bit encrypted output using a 56-bit master key. • The DES algorithm is difficult to break using analytical methods ((the rationale behind the design has never been clearly explained). Using a brute-force attack will do the job because the key length is 56 bits. In June 1997, it was successfully cracked. Only used for the protection of low-value information. • Triple-DES: apply DES three times with another two different keys. Give strength against brute-force attacks. • Advanced Encryption Standard (AES). • In 1997, the US NIST (National Institute of Standards and Technology) issued an invitation for Advanced Encryption Standard (AES). • NIST announced the approval of the Federal Information Processing Standard (FIPS) for the Advanced Encryption Standard, FIPS-197. • This standard specifies Rijndael algorithm (blocks of 128 bits) as a FIPS-approved symmetric encryption algorithm that may be used by U.S. Government organizations (and others) to protect sensitive information. • The algorithm has been designed to be fast enough so that it can even be implemented on smart cards.
Data Encryption Standard • The data encryption standard. (a) General outline.(b) Detail of one iteration. The circled + means exclusive OR.
Triple DES • (a) Triple encryption using DES. (b) Decryption.
Stream Cipher Mode • A stream cipher. (a) Encryption. (b) Decryption.
Cryptanalysis • Some common symmetric-key cryptographic algorithms.
Public-Key Cryptography • Asymmetric (Public-key) cryptography uses an encryption algorithm E and a decryption algorithm D such that deriving D is effectively impossible even with a complete description of E. You can encrypt without knowing how to decrypt. • Requirements: • D (E(P)) = P • It is extremely difficult to deduce the decryption key from the encryption key. • E cannot be broken by a plaintext attack. • All users pick a public key/private key pair • publish the public key • private key not published • Public key is the encryption key • private key is the decryption key
Public-Key Cryptosystems: RSA • RSA • RSA, named after its inventors Rivest, Shamir, and Adlemean, a public-key cryptographic algorithm. • The security of RSA comes from the fact that no methods are known to efficiently find the prime factors to large numbers. • For example, 2100 can be written as 2100 = 2 x 2 x 3 x 5 x 5 x 7 making 2, 3, 5, and 7 the prime factors in 2100. • In RSA, the private and public keys are constructed from very large prime numbers. It turns out breaking RSA is equivalent to finding those two prime numbers.
Public-Key Cryptosystems: RSA • Generating the private and public key requires four steps: • Choose two very large prime numbers, p and q • Compute n = p x q and z = (p – 1) x (q – 1) • Choose a number d that is relatively prime to z (that is, such that d has no common factors with z) • Compute the number e such that e x d = 1 mod z • Group P into blocks such that C=Pe (mod n) and P=Cd(mod n) where 0 <= P < n
Public-Key Cryptography • Example: p=13 q=17 n = 13 x 17 = 221 z = (13 – 1) x (17 – 1) = 192. let d=5 (prime to z) e x d = 1 mod 192 = 1, 193, 385, ... 385 is divisible by d e = 385/5 = 77 • Example: p=3 q=11 n = 3 x 11 = 33 z = (3 – 1) x (11 – 1) = 20. let d=7 (prime to z) 7 x e mod 20 = 1 e=3 C = P3 (mod 33), P = C7 (mod 33)
RSA • An example of the RSA algorithm.
Hashing system • Hashing System • Oneway function: Given some output mout of ES , it is (analytically or) computationally infeasible to find min • Weak collision resistance: Given an input m and its associated output h = H(m) it is computationally infeasible to find an m’ such that H(m) = H(m’). • Strong collision resistance: given only H, it is computationally infeasible to find any two different inputs m and m’ such that H(m) = H(m’). • One way function: • Function such that given formula for f(x) • easy to evaluate y = f(x) • But given y • computationally infeasible to find x • Example: Those functions used in public-key cryptography.
Digital Signatures • Digital signatures make it possible to sign email messages and other digital documents in such a way that they cannot be repudiated by the sender later. • Steps to use digital signatures: • The sender runs the document through a one-way hashing algorithm • The sender applies his private key to the hash to get D(hash). This is called the signature block. • The receiver computes the hash of the document using MD5 or SHA and then applies the sender’s public key to the signature block to get E(D(hash)). Compare hash and E(D(hash)).
Digital Signatures • Computing a signature block • What the receiver gets (b)
Digital Signatures • The most popular hashing functions used are: • MD5 (Message Digest) which produces a 16-byte result. • SHA (Secure Hash Algorithm) which produces a 20-byte result. • The public key is usually published. To avoid altering, message senders can attach a certificate to the message, which contains: • The user’s name • The public key • Digitally singed by a trusted third party
Hash Functions • Secure Hash Algorithm (SHA), • which produces a 256-bit message digest. This provides protection of the integrity of encrypted files as well as public key files. • SHA was developed by the NIST in the United States, who announced the approval of FIPS 180-2, Secure Hash Standard, containing the specifications for the Secure Hash Algorithm SHA-256. • MD5 • MD5 (Message Digest 5) is an algorithm that is used to verify data integrity through the creation of a 128-bit message digest from data input which may be a message of any length. • MD5, which was developed by Professor Ronald L. Rivest of MIT, is intended for use with digital signature applications, which require that large files must be compressed by a secure method before being encrypted with a secret key, under a public key cryptosystem. • MD5 is currently a standard, Internet Engineering Task Force (IETF) Request for Comments (RFC) 1321.
Certificates • A possible certificate and its signed hash.
X.509 • X.509 is the ITU-T (International Telecommunications Union-T) standard for Digital Certificates. • The basic fields of an X.509 certificate.
Public-Key Infrastructures • A Public Key Infrastructure (PKI) integrates software, hardware, encryption technologies and services for managing the cryptographic infrastructure and users' public keys. (a) A hierarchical PKI. (b) A chain of certificates.
IPsec (IP Security) • The IPsec authentication header in transport mode for IPv4.
IPsec (2) (a) ESP in transport mode. (b) ESP in tunnel mode.
Rest of the Internet Firewall Local site Firewalls • A firewall is a set of related programs, located at a network gateway server, that protects the resources of a private network from users from other networks.