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Application Layer Security

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Presentation on theme: "Application Layer Security"— Presentation transcript:

1 Application Layer Security

2 Outline security Web security Social networking security

3 security is one of the most widely used and regarded network services; essentially file transfer, except: Sender and receiver not present at same time Has diversity (character sets, headers, …) Not a transparent channel (8 bit data, CRLF) Often across realms Currently message contents are not secure May be inspected either in transit Or by suitably privileged users on destination system Often principals have not met previously ⇒ use chain of certificates Current services are roughly like "postcards". Anyone who wants could pick it up and have a look as its in transit or sitting in the recipients mailbox.

4 Email security enhancements
Confidentiality: protection from disclosure Authentication: of sender of message Message integrity: protection from modification Non-repudiation of origin: protection from denial by sender Accounting, self-destruction, audit, anonymity, proof of delivery… What we want is something more akin to standard mail (contents protected inside an envelope) if not registered mail (have confidence about the sender of the mail and its contents).

5 Internet Email Protocol: SMTP:
ASCII commands, responses Separate headers from envelope TCP port 25 Uses DNS Binary content, structure MIME (multipurpose Internet mail extensions) Note: Mail servers and agents use SMTP for exchange, clients use SMTP typically for relaying only, preferring POP/IMAP for receiving What we want is something more akin to standard mail (contents protected inside an envelope) if not registered mail (have confidence about the sender of the mail and its contents).

6 Secure Email . - Alice wants to send confidential email, m, to Bob.
KS( ) . KB( ) + - KS(m ) KB(KS ) m KS KB Internet Alice: Generates random symmetric private key, KS Encrypts message with KS (for efficiency) Also encrypts KS with Bob’s public key Sends both KS(m) and KB(KS) to Bob Network Security

7 Secure Email . - Alice wants to send confidential email, m, to Bob.
KS( ) . KB( ) + - KS(m ) KB(KS ) m KS KB Internet Bob: Uses his private key to decrypt and recover KS Uses KS to decrypt KS(m) to recover m Network Security

8 Secure E-mail (Continued)
Alice wants to provide sender authentication message integrity H( ) . KA( ) - + H(m ) KA(H(m)) m KA Internet compare Alice digitally signs message Sends both message (in the clear) and digital signature Network Security

9 Secure Email (Continued)
Alice wants to provide secrecy, sender authentication, message integrity. H( ) . KA( ) - + KA(H(m)) m KA KS( ) KB( ) KB(KS ) KS KB Internet Alice uses three keys: her private key, Bob’s public key, newly created symmetric key Network Security

10 Pretty Good Privacy (PGP)
Widely used confidentiality and authentication service for securing electronic mail and other file storage applications Developed by Phil Zimmermann Selected best available crypto algorithms to use Integrated into a single program available on PC, Macintosh, Linux systems Free and commercial versions (e.g., GPG)

11 PGP Operation Summary Stallings Fig 15-2.

12 Why Johnny (Still) Can’t Encrypt
Usability studies (1999, 2007) showed majority of users could not properly encrypt using PGP The user interface is not intuitive enough Transparency of encryption/signature is confusing Users seem to need feedback that was secured Verification is confusing Users don’t follow the reasoning for verification

13 Outline security Web security Social networking security

14 The Web Web page: User agent for Web is called a browser:
Consists of “objects” Addressed by a URL Most Web pages consist of: Base HTML page, and Several referenced objects. URL has two components: host name and path name User agent for Web is called a browser: MS Internet Explorer Netscape Communicator Server for Web is called Web server: Apache (public domain) MS Internet Information Server Nginx (public domain)

15 The Web: the HTTP Protocol
HTTP: HyperText Transfer Protocol Web’s application layer protocol Client/server model Client: browser that requests, receives, “displays” Web objects Server: Web server sends objects in response to requests HTTP 1.0: RFC 1945 HTTP 1.1: RFC 2068 HTTP request PC running Explorer HTTP response HTTP request Server running NCSA Web server HTTP response Mac running Navigator

16 The HTTP Protocol (more)
HTTP: TCP transport service: Client initiates TCP connection (creates socket) to server, port 80 Server accepts TCP connection from client HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server) TCP connection closed HTTP is “stateless” Server maintains no information about past client requests aside Protocols that maintain “state” are complex! Past history (state) must be maintained If server/client crashes, their views of “state” may be inconsistent, must be reconciled

17 HTTP Example Suppose user enters URL (contains text, references to 10 JPEG images) 1a. HTTP client initiates TCP connection to http server (process) at Port 80 is default for HTTP server. 1b. HTTP server at host waiting for TCP connection at port 80. “Accepts” connection, notifies client 2. HTTP client sends http request message (containing URL) into TCP connection socket 3. HTTP server receives request message, forms response message containing requested object (aDepartment/index.html), sends message into socket time

18 HTTP Example (Cont.) time 4. HTTP server closes TCP connection.
5. HTTP client receives response message containing HTML file, displays HTML. Parsing HTML file, finds 10 referenced JPEG objects time 6. Steps 1-5 repeated for each of 10 JPEG objects

19 HTTP Message Format: Request
Two types of HTTP messages: request, response HTTP request message: ASCII (human-readable format) request line (GET, POST, HEAD commands) GET /somedir/page.html HTTP/1.0 User-agent: Mozilla/4.0 Accept: text/html, image/gif,image/jpeg Accept-language:fr (extra carriage return, line feed) header lines Carriage return, line feed indicates end of message

20 HTTP Message Format: Response
status line (protocol status code status phrase) HTTP/ OK Date: Thu, 06 Aug :00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 1998 …... Content-Length: 6821 Content-Type: text/html data data data data data ... header lines data, e.g., requested html file

21 Threat: Information Leakage
Sensitive information can be leaked via Web: All files accessible under a Web directory can be downloaded via GET requests Example 1: publicly accessible has no link to secret.jpg Attacker can still download secret.jpg via GET request! Example 2: searching online for “proprietary confidential” information

22 Threat: Misleading Websites
Cybersquatters can register domain names similar to (trademarked) company, individual names Example: vs. vs. … Practice is illegal if done “in bad faith” Arbitration procedures available for name reassignment (ICANN)

23 Threat: XSS and CSRF Cross-site scripting (XSS): inject JavaScript from external source into insecure websites Example: input <script type=“text/javascript”><!--evil code--></script> Cross-site request forgery (CSRF): force victim browser to send request to external website → performs task on browser’s behalf Example: force load <img src=“

24 Threat: SQL Injection Common vulnerability (~71 attacks/hour [18])
Exploits Web apps that [17, 19] Poorly validate user input for SQL string literal escape characters, e.g., ' Example: [19] "SELECT * FROM users WHERE name = '" + userName + "';" If userName is set to ' or '1'='1, the resulting SQL is SELECT * FROM users WHERE name = '' OR '1'='1'; This evaluates to SELECT * FROM users ⇒ displays all users

25 Threat: Malicious Shellcode
Shellcode is non-self-contained binary executable code Distinct from malware that executes on its own Shellcode can only execute after injection into a running process’s virtual address space Most shellcode written in Intel IA-32 assembly language (x86) When injected into JS code, shellcode executes Hijacks browser process Can totally control target process or system Shellcode: attack vector for malicious code execution on target systems (e.g., Conficker worm) Usually, browser downloads JS code containing shellcode JS code executes, controls target process/system

26 Threat: Shellcode Example
mov ebx, 0 mov eax, 1 int 0x80 Shellcode for exit() system call Store 0 into register ebx Store 1 into register eax Execute instruction int 0x80 Assembled shellcode injected into JS code Shellcode assembly bb b cd 80 Binary payload injection JS code ...3caabb b cd80ad46... more JS code Disguised as normal data; injected into target processes’ address spaces; compromises target processes’ security

27 Defense: HTTPS (HTTP Secure)
HTTPS uses cryptography with HTTP (TLS, SSL) Alice, Bob have public, private keys; public keys accessible via certificate authority (CA) Alice encrypts message with Bob’s public key, signs message with her private key Bob decrypts message with his private key, verifies message using Alice’s public key Once they “know” each other, they can communicate via symmetric crypto keys HTTPS provides greater assurance than HTTP

28 Defense: Blacklist Filtering (1)
Misleading websites: register domain names similar to trademarks, e.g., gogle.com, etc. XSS: Validate user input; reject invalid input Blacklist offending IP addresses CSRF: Use random “token” in web app forms If token is replayed, reject form (blacklist IP addresses) SQL injection: Validate user input to databases, reject invalid input Blacklist IP addresses Helpful browser extensions: NoScript/NotScripts/… (stop XSS) AdBlock (can stop malicious scripts in ads) SSL Everywhere (force HTTPS) Google Safe Browsing

29 Defense: Shellcode Two main detection approaches: Content Analysis
Checks objects’ contents before using them Decodes content into instruction sequences, checks if malicious Hijack Prevention Focuses on preventing shellcode from being fully executed Randomly inserts special bytes into objects’ contents, raises exception if executed Can be thwarted using several short “connected” shellcodes

30 Defense: Shellcode: Content Analysis
Two major types of content analysis: Static Analysis Uses signatures, code patterns to check for malicious instructions Advantage: Fast Disadvantages: Incomplete; can be thwarted by obfuscation techniques Dynamic Analysis Detects a malicious instruction sequence by emulating its execution Advantages: Resistant to obfuscation; more complete than static analysis Disadvantage: Slower Focus on dynamic analysis (greater completeness)

31 Defense: Shellcode: Dynamic Analysis
Approaches assume self-contained shellcodes Analyses’ shellcode emulation: Inefficiently uses JS code execution environment information All memory reads/writes only go to emulated memory system Detection uses GetPC code Current dynamic analysis approaches can be fooled: Shellcode using JS code execution environment info Shellcode using target process virtual memory info Shellcode not using GetPC code To detect all malicious shellcodes, we need a better approach

32 Defense: Shellcode: JSGuard (1)
Our design rationale: [20] Use dynamic analysis to detect malicious JS objects Create a virtual execution environment for detection Leveraging: (1) target processes’ virtual memory information; (2) target systems’ context information in detection NOT a whole-system emulator Facilitate multiple-level redundancy reduction Stack frames: check origins of JS code being interpreted Native methods: check if native methods to be called originate from JS interpreter or external components Objects’ properties Assume: JS interpreter’s (native) methods have no memory errors

33 Defense: Shellcode: JSGuard (2)
It’s hard to fool our method: [20] Shellcode can use JS code execution environment information to fool other dynamic analysis approaches Our design leverages system’s context information Shellcode can use target process’s virtual memory information to fool other dynamic analysis approaches Our design uses target processes’ virtual memory information Shellcode can avoid GetPC code to fool other dynamic analysis approaches Our method does not rely on GetPC code for detection. We leverage real virtual memory content to decode instructions and emulate their execution

34 Defense: Shellcode: JSGuard (3)
JSGuard architecture shown in figure below [20] We mainly check JSString objects for shellcode injection (hard to inject shellcode in other JS objects) Architecture runs in client-side application’s address space (Firefox browser) JSString objects input to malicious JSString detector, which scans for shellcode using shellcode analyzer Source: [20]

35 Outline security Web security Social networking security

36 Online Social Networking (OSN)
Online Web services enabling people to connect with each other, share information Common friends, interests, personal info… Post photos, videos, etc. for others to see Communicate via , instant message, etc. Major OSN services: Facebook, Twitter, MySpace, LinkedIn, etc.

37 Benefits of OSN Communication
Vast majority of college students use OSNs Organizations want to market products, services, etc. to this demographic OSNs can help them reach these potential buyers OSNs provide communal forum for expression (self, group, mass), collaboration, etc. Connect with old friends, find new friends and connect Play games with friends, e.g., Mafia Wars, Scrabulous Commerce in “virtual items” But using OSNs poses security issues for orgs as well as individuals

38 Mobile Social Networking (MSN)
E-SmallTalker E-Shadow

39 Small Talk People come into contact opportunistically
Face-to-face interaction Crucial to people's social networking Immediate non-verbal communication Helps people get to know each other Provides the best opportunity to expand social network Small talk is an important social lubricant Difficult to identify significant topics Superficial

40 A Naive Approach of Smartphone-based Small Talk
Main Idea Problems Store all user information, including each user’s full contact list User report either his own geo-location or a collection of phone IDs in his physical proximity to the server using Internet connection, SMS Server performs profile matching, finds out small talk topics (mutual contact, common interests, etc.) Results are pushed to or retrieved by users Require costly data services (phone’s internet connection, SMS) Require report and store sensitive personal information in 3rd party Trusted server may not exist Server is a bottleneck, single point of failure, target of attack

41 E-SmallTalker – A Fully Distributed Approach
No Internet connection required No trusted 3rd party No centralized server Information stored locally on mobile phones Original personal data never leaves a user’s phone Communication only happens in physical proximity

42 E-Shadow Enhanced E-SmallTalker Local profiles
Mobile phone based local social interaction tools E-Shadow publishing E-Shadow localization

43 Threats: OSNs Malware distribution Cyber harassment, stalking, etc.
Information “shelf life” in cyberspace Privacy issues: Information about person posted by him/herself, others Information about people collected by OSNs Information posted on OSNs impacts unemployment, insurance, etc. Organizations’ concerns: brand, laws, regulations

44 Threats: MSN Personal information leakage Malware distribution
Particularly dangerous because of physical proximity Malware distribution

45 Defense: OSN “Common Sense” Measures (1)
Use strong, unique passwords Provide minimal personal information: avoid entering birthdate, address, etc. Review privacy settings, set them to “maximum privacy” “Friends of friends” includes far more people than “friends only” Exercise discretion about posted material: Pictures, videos, etc. Opinions on controversial issues Anything involving coworkers, bosses, classmates, professors Anything related to employer (unless authorized to do so) Be wary of 3rd party apps, ads, etc. (P.T. Barnum’s quote) Supervise children’s OSN activity

46 Defense: OSN “Common Sense” Measures (2)
“If it sounds too good to be true, it probably is” Use browser security tools for protection: Anti-phishing filters (IE, Firefox) Web of Trust (crowdsourced website trust) AdBlock/NoScript/Do Not Track Plus Personal reputation management: Search for yourself online, look at the results… Google Alerts: s sent daily to you about results for any search query (free), e.g., your name Extreme cases: Cease using OSNs, delete accounts Contact law enforcement re. relentless online harassment

47 Defense: MSN: E-SmallTalker: Privacy-Preserved Information Exchange
Example of Alice’s Bloom filter Alice has multiple contacts, such as Bob, Tom, etc. Encode contact strings, such as and

48 Defense: MSN: E-Shadow: Layered Publishing
Spatial Layering WiFi SSID at least meters, 32 Bytes Bluetooth Device (BTD) Name 20 meters, 2k Bytes Bluetooth Service (BTS) Name 10 meters, 1k Bytes Temporal Layering For people being together long or repeatedly Erasure Code

49 Final Remarks Unencrypted email is easily intercepted
PGP, GPG can provide confidentiality, integrity, client authentication via encryption Web traffic vulnerable to attacks Defenses include domain name registration, blacklists, browser extensions, and malicious code detection Social networking attacks are possible both online and via mobiles Follow “common sense” for online social networks Mechanisms like Bloom filters, layered publishing can help safeguard personal information

50 Acknowledgment These slides are partially based on: J.F. Kurose and K.W. Ross, Computer Networking: A Top-Down Approach Featuring the Internet, Addison Wesley, 2011 A. Arora, “Lecture 5: security: PGP”, W. Stallings, Network Security Essentials, Pearson, 2014, (Ch. 8) A.C. Champion and D. Xuan’s CSE 4471 slides,


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