Dr. Frank Li

 Pro and Con of Asymmetric / Symmetric cryptosystem  DH key exchange and RSA  Digital Certificate and Digital Signatures  AAA service - Kerbros

 Asymmetric algorithm works much more slowly than a symmetric algorithm  Symmetric algorithms carry out relatively simplistic mathematical functions – substitution and transposition  Asymmetric algorithm uses much more complex mathematics to carry out their functions  Asymmetric algorithms  Can provide authentication and non-repudiation.  also provide for easier and more manageable key distribution 3

 Pro: Asymmetric algorithms  Can provide authentication and non-repudiation.  also provide for easier and more manageable key distribution  Cons: Asymmetric algorithm works much more slowly than a symmetric algorithm  Symmetric algorithms carry out relatively simplistic mathematical functions – substitution and transposition  Asymmetric algorithm uses much more complex mathematics to carry out their functions.

 Diffie-Hellman algorithm, a.k.a. Diffie-Hellman (D-H) key exchange  Was invented in 1976  is a cryptographic protocol that allows two parties that jointly establish a shared secret key over an insecure communications channel.  This key can then be used to encrypt subsequent communications using a symmetric key cipher. 5

6 Alice and Bob share a prime p and g. g < p g is a primitive root of p (detail is not required in this course)

 RSA, named after its inventors Ron Rivest, Adi Shamir, and Leonard Adleman, in 1977  de facto standard used for digital signatures, key exchange, and encryption.  The security of RSA comes from the difficulty of factoring large numbers.  The public and private keys are functions of a pair of large prime numbers  RSA is the most popular public key algorithm. It has been implemented in applications, operating systems, and at the hardware level in network interface cards, secure telephones, and smart cards. 7

1. Choose two random large prime numbers, p and q. and generate the product: n = pq. 2. Choose a random number e. So that e and  (n) = ( p – 1)( q – 1) are relatively prime. 3. Compute the decryption key d. e d = 1 mod  (n) (calculate d by using Extended Euclidean algorithm) The public key = (n, e), the private key = d. 8

9 Modulo operations are computational expensive. Thus, public cryptosystem is slower than symmetric cryptosystems.

 A potential weakness of public-key cryptography Q: How do you know that the pubic key you have for an individual is really for that individual?  The solution is authentication public key  Authentication is the process of proving that you are in fact the person you say you are.  E.g., A phone ID is commonly used to authenticate a person. Q: How to authenticate a public key?

 Signatures let you authenticate a public key  How the signature works?  You verify that another person’s key really belongs to that person. And then sign that public key with your own private key.  Others get that public key can see your signature and know you trust that key, so they may decide to trust it OR may decide to verify that key themselves.  Form a web of trust -- a peer to peer trust relationship  Example … Q: How to verify another person’s public key?

 Verify the public key in person or call the owner of the public key and check the key  A key usually has hundred of digits  Check bit by bit is not very efficient  A fingerprint is a smaller number that is derived from a very lengthy public key  Fingerprints are created by hashing the public key,  Hashing is a process by which a mathematical function is used that converts larger numbers into smaller numbers

Using digital certificate -- with PKI  A certificate is a numeric code that is used to identify an organization  Certificate authority (CA) verifies the credential of an organization or individual.  Then CA issues a client’s public key and sign it with CA’s private key E.g. VeriSign is an well-known CA

Encrypted TGS ticket Joe the User Key distribution center (KDC) USER=Joe; service=TGS uProve identity once to obtain special TGS ticket Instead of password, use key derived from password uUse TGS to get tickets for many network services File server, printer, other network services Encrypted service ticket Ticket granting service (TGS) TGS ticket Encrypted service ticket

 Client only needs to obtain TGS ticket once (say, every morning)  Ticket is encrypted; client cannot forge it or tamper with it User kinit program (client) Key Distribution Center (KDC) password ID c, ID TGS, time c Encrypt K c (K c,TGS, ID TGS, time KDC, lifetime, ticket TGS ) KcKc Convert into client master key Key = K c Key = K TGS TGS … All users must pre-register their passwords with KDC Fresh key to be used between client and TGS Decrypts with K c and obtains K c,TGS and ticket TGS Encrypt K TGS (K c,TGS, ID c, Addr c, ID TGS, time KDC, lifetime) Client will use this unforgeable ticket to get other tickets without re-authenticating

 Client uses TGS ticket to obtain a service ticket and a short-term key for each network service  One encrypted, unforgeable ticket per service (printer, , etc.) User Client Ticket Granting Service (TGS) usually lives inside KDC System command, e.g. “lpr –Pprint” ID v, ticket TGS, auth C Encrypt K c,TGS (K c,v, ID v, time TGS, ticket v ) Fresh key to be used between client and service Knows K c,TGS and ticket TGS Encrypt K c,TGS (ID c, Addr c, time c ) Proves that client knows key K c,TGS contained in encrypted TGS ticket Encrypt K v (K c,v, ID c, Addr c, ID v, time TGS, lifetime) Client will use this unforgeable ticket to get access to service V Knows key K v for each service

 For each service request, client uses the short-term key for that service and the ticket he received from TGS User Client Server V System command, e.g. “lpr –Pprint” ticket v, auth C Encrypt K c,v (time c +1) Knows K c,v and ticket v Encrypt K c,v (ID c, Addr c, time c ) Proves that client knows key K c,v contained in encrypted ticket Authenticates server to client Reasoning: Server can produce this message only if he knows key K c,v. Server can learn key K c,v only if he can decrypt service ticket. Server can decrypt service ticket only if he knows correct key K v. If server knows correct key K v, then he is the right server.

 Use of short-term session keys  Minimize distribution and use of long-term secrets; use them only to derive short-term session keys  Separate short-term key for each user-server pair  But multiple user-server sessions reuse the same key!  Proofs of identity are based on authenticators  Client encrypts his identity, address and current time using a short-term session key  Also prevents replays (if clocks are globally synchronized)  Server learns this key separately (via encrypted ticket that client can’t decrypt) and verifies user’s identity

 , FTP, network file systems and many other applications have been kerberized  Use of Kerberos is transparent for the end user  Transparency is important for usability!  Local authentication  login and su in OpenBSD  Authentication for network protocols  rlogin, rsh, telnet  Secure windowing systems  xdm, kx

Network Access Control and Cloud Security

 An umbrella term for managing access to a network  Authenticates users logging into the network and determines what data they can access and actions they can perform  Also examines the health of the user’s computer or mobile device

NAC systems deal with three categories of components: Access requester (AR) Node that is attempting to access the network and may be any device that is managed by the NAC system, including workstations, servers, printers, cameras, and other IP-enabled devices Also referred to as supplicants, or clients Policy server Determines what access should be granted Often relies on backend systems Network access server (NAS) Functions as an access control point for users in remote locations connecting to an enterprise’s internal network Also called a media gateway, remote access server (RAS), or policy server May include its own authentication services or rely on a separate authentication service from the policy server

 The actions that are applied to ARs to regulate access to the enterprise network  Many vendors support multiple enforcement methods simultaneously, allowing the customer to tailor the configuration by using one or a combination of methods Common NAC enforcement methods: IEEE 802.1X Virtual local area networks (VLANs) Firewall DHCP management

 EAP provides a generic transport service for the exchange of authentication information between a client system and an authentication server  The basic EAP transport service is extended by using a specific authentication protocol that is installed in both the EAP client and the authentication server Commonly supported EAP methods: EAP Transport Layer Security EAP Tunneled TLS EAP Generalized Pre-Shared Key EAP-IKEv2

Table 5.1 Terminology Related to IEEE 802.1X

 NIST defines cloud computing, in NIST SP (The NIST Definition of Cloud Computing ) “A model for enabling ubiquitous, convenient, on- demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models.”

 NIST SP (NIST Cloud Computing Reference Architecture ) “The NIST cloud computing reference architecture focuses on the requirements of “what” cloud services provide, not a “how to” design solution and implementation. The reference architecture is intended to facilitate the understanding of the operational intricacies in cloud computing. It does not represent the system architecture of a specific cloud computing system; instead it is a tool for describing, discussing, and developing a system-specific architecture using a common framework of reference.”

Cloud provider (CP) Can provide one or more of the cloud services to meet IT and business requirements of cloud consumers For each of the three service models (SaaS, PaaS, IaaS), the CP provides the storage and processing facilities needed to support that service model, together with a cloud interface for cloud service consumers For SaaS, the CP deploys, configures, maintains, and updates the operation of the software applications on a cloud infrastructure so that the services are provisioned at the expected service levels to cloud consumers For PaaS, the CP manages the computing infrastructure for the platform and runs the cloud software that provides the components of the platform, such as runtime software execution stack, databases, and other middleware components For IaaS, the CP acquires the physical computing resources underlying the service, including the servers, networks, storage, and hosting infrastructure Cloud Provider

Cloud carrier A networking facility that provides connectivity and transport of cloud services between cloud consumers and CPs Cloud broker Useful when cloud services are too complex for a cloud consumer to easily manage Three areas of support can be offered by a cloud broker: Service intermediation Value-added services such as identity management, performance reporting, and enhanced security Service aggregation The broker combines multiple cloud services to meet consumer needs not specifically addressed by a single CP, or to optimize performance or minimize cost Service arbitrage A broker has the flexibility to choose services from multiple agencies Cloud auditor An independent entity that can assure that the CP conforms to a set of standards

 The Cloud Security Alliance [CSA10] lists the following as the top cloud specific security threats, together with suggested countermeasures: Countermeasures: stricter initial registration and validation processes; enhanced credit card fraud monitoring and coordination; comprehensive introspection of customer network traffic; monitoring public blacklists for one’s own network blocks Abuse and nefarious use of cloud computing Countermeasures: enforce strict supply chain management and conduct a comprehensive supplier assessment; specify human resource requirements as part of legal contract; require transparency into overall information security and management practices, as well as compliance reporting; determine security breach notification processes Malicious insiders

Insecure interfaces and APIs Countermeasures: analyzing the security model of CP interfaces; ensuring that strong authentication and access controls are implemented in concert with encryption machines; understanding the dependency chain associated with the API Shared technology issues Countermeasures: implement security best practices for installation/configuration; monitor environment for unauthorized changes/activity; promote strong authentication and access control for administrative access and operations; enforce SLAs for patching and vulnerability remediation; conduct vulnerability scanning and configuration audits Data loss or leakage Countermeasures: implement strong API access control; encrypt and protect integrity of data in transit; analyze data protection at both design and run time; implement strong key generation, storage and management, and destruction practices

 Account or service hijacking  Countermeasures: prohibit the sharing of account credentials between users and services; leverage strong two-factor authentication techniques where possible; employ proactive monitoring to detect unauthorized activity; understand CP security policies and SLAs  Unknown risk profile  Countermeasures: disclosure of applicable logs and data; partial/full disclosure of infrastructure details; monitoring and alerting on necessary information

Table 5.3 NIST Guidelines on Security and Privacy Issues and Recommendation s (page 1 of 2) (Table can be found on Pages 154 – 155 in textbook)

Table 5.3 NIST Guidelines on Security and Privacy Issues and Recommendation s (page 2 of 2) (Table can be found on Pages 154 – 155 in textbook)

 The threat of data compromise increases in the cloud  Database environments used in cloud computing can vary significantly Provides a unique DBMS running on a virtual machine instance for each cloud subscriber This gives the subscriber complete control over role definition, user authorization, and other administrative tasks related to security Multi-instance model Provides a predefined environment for the cloud subscriber that is shared with other tenants, typically through tagging data with a subscriber identifier Tagging gives the appearance of exclusive use of the instance, but relies on the CP to establish and maintain a sound secure database environment Multi-tenant model

 Data must be secured while at rest, in transit, and in use, and access to the data must be controlled  The client can employ encryption to protect data in transit, though this involves key management responsibilities for the CP  For data at rest the ideal security measure is for the client to encrypt the database and only store encrypted data in the cloud, with the CP having no access to the encryption key  A straightforward solution to the security problem in this context is to encrypt the entire database and not provide the encryption/decryption keys to the service provider  The user has little ability to access individual data items based on searches or indexing on key parameters  The user would have to download entire tables from the database, decrypt the tables, and work with the results  To provide more flexibility it must be possible to work with the database in its encrypted form

 The Cloud Security Alliance defines SecaaS as the provision of security applications and services via the cloud either to cloud-based infrastructure and software or from the cloud to the customers’ on-premise systems  The Cloud Security Alliance has identified the following SecaaS categories of service:  Identity and access management  Data loss prevention  Web security  security  Security assessments  Intrusion management  Security information and event management  Encryption  Business continuity and disaster recovery  Network security

 Network access control  Elements of a network access control system  Network access enforcement methods  Extensible authentication protocol  Authentication methods  EAP exchanges  Cloud security as a service  IEEE 802.1X port-based network access control  Cloud computing  Elements  Reference architecture  Cloud security risks and countermeasures  Data protection in the cloud