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Review For Exam 3 © Abdou Illia – Spring 2012. The Elements of Cryptography.

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Presentation on theme: "Review For Exam 3 © Abdou Illia – Spring 2012. The Elements of Cryptography."— Presentation transcript:

1 Review For Exam 3 © Abdou Illia – Spring 2012

2 The Elements of Cryptography

3 3 Cryptography? Traditionally, cryptography refers to The practice and the study of encryption Transforming information in order to prevent unauthorized people to read it. Today, cryptography goes beyond encryption/decryption to include Techniques for making sure that encrypted messages are not modified en route Techniques for secure identification/authentication of communication partners.

4 4 Your knowledge about Cryptography Which of the following security issues is addressed by cryptographic systems? a) Confidentiality; i.e. protection against eavesdropping b) Authentication; i.e. assurance parties involved in a communication are who they claim to be c) Message integrity; i.e. assurance that messages are not altered en route d) Availability; i.e. making sure that communication systems are not shut down by intruders. e) All of the above

5 5 Basic Terminology 1 Network Plaintext “Hello” Ciphertext “11011101” Plaintext “Hello” Decryption Algorithm Interceptor Party A Party B Plaintext: original message to be sent. Could be text, audio, image, etc. Encryption/Decryption Algorithm: mathematical tool (software) used to encrypt or decrypt Key: A string of bits used by to encrypt the plaintext or decrypt the ciphertext Ciphertext: encrypted message. Looks like a random stream of bits + Decryption key Encryption Algorithm + Encryption key

6 6 Basic Terminology 2 Encryption: Converting plaintext into ciphertext using algorithms and keys The size of the ciphertext is proportional to the size of the plaintext Ciphertext is reversible to plaintext Symmetric Key Encryption: Same key is used both for encryption and decryption Keys are usually identical or trivially identical* Asymmetric Key Encryption: Also called Public/Private Key Encryption Two different keys are used: one for encryption, one for decryption Party A Party B Party A Party B * Trivially identical means simple transformation could lead from one key to the another. Flexcrypt: http://www.flexcrypt.com/flexcryptfree.htmlhttp://www.flexcrypt.com/flexcryptfree.html

7 7 Your knowledge about Cryptography 1) Based on how symmetric encryption systems work, which of the following is the worst thing to happen? a) An attacker gets a copy of the encryption and decryption algorithms b) An attacker gets the decryption key c) a and b are equally damaging 2) Which of the following presents more challenge for exchanging keys between partners? a) Asymmetric encryption b) Symmetric encryption c) A and b are equally challenging

8 8 Exhaustive search and Key length Key Length in bitsNumber of possible keys (2 key length in bits ) 12 24 416 8256 1665536 5672057594037927900 1125192296858534830000000000000000000 or 5.1923E+33 1683.74144E+50 2561.15792E+77 5121.3408E+154 Attacker could use the right algorithm and do an exhaustive search (i.e. try all possible keys) in order to decrypt the ciphertext Most attacks require the capture of large amount of ciphertext Every additional bit in the length of the key doubles the search time

9 9 Your knowledge about Cryptography 4)If you increase the key length from 56 bits to 66 bits. How much more key combinations an attacker who captures enough ciphertext will have to try in order to decipher the captured ciphertext using the appropriate algorithm? _______________________________________ 5)Assuming that it takes 7 days to try all possible combinations of a 56 bit key, how much time it would take to try all possible combinations when the key length is increased to 58 bits? ________________

10 10 Weak vs. Strong Keys Symmetric Key Encryption Usually used for customer e-business Keys with lengths of less than 100 bits are considered weak today. Keys with lengths of more than 100 bits are considered strong today. Asymmetric Key Encryption Usually used for B2B financial e-business Key pairs must be much longer (1024 bits and more) because of the disastrous consequences of breaking the decryption key Key Length in bits Number of possible keys ( 2 key length in bits ) 12 24 1665536 5672057594037927900 1125192296858534830000000000000000000 or 5.1923E+33 1683.74144E+50 2561.15792E+77 5121.3408E+154

11 11 Your knowledge about Cryptography 6)Most attacks require the capture of large amount of ciphertext, which can take a certain amount of time. Beside using strong keys what else can be done to make it harder to crack the key?

12 Symmetric Key Encryption

13 13 Symmetric Key Encryption methods Two categories of methods Stream cipher: algorithm operates on individual bits (or bytes); one at a time Block cipher: operates on fixed-length groups of bits called blocks Only a few symmetric methods are used today MethodsYear approvedComments Data Encryption Standard - DES19771998: Electronic Frontier Foundation’s Deep Crack breaks a DES key in 56 hours DES-Cipher Block Chaining Triple DES – TDES or 3DES1999 Advanced Encryption Standard – AES2001Its versions among the most used today Other symmetric encryption methods IDEA (International Data Encryption Algorithm), RC5 (Rivest Cipher 5), CAST (Carlisle Adams Stafford Tavares), Blowfish

14 14 Data Encryption Standard (DES) DES Encryption Process 64-Bit Ciphertext Block 64-Bit DES Symmetric Key (56 bits + 8 redundant bits) 64-Bit Plaintext Block DES is a block encryption method, i.e. uses block cipher DES uses a 64 bit key; actually 56 bits + 8 bits computable from the other 56 bits Problem: same input plaintext gives same output ciphertext

15 15 DES-Cipher Block Chaining First 64-Bit Plaintext Block DES Encryption Process Second 64-Bit Plaintext Block First 64-Bit Ciphertext Block Initialization Vector (IV) DES Encryption Process Second 64-Bit Ciphertext Block DES Key DES-CBC uses ciphertext from previous block as input making decryption by attackers even harder An 64-bit initialization vector is used for first block

16 16 Triple DES (3DES) SenderReceiver Encrypts original plaintext with the 1 st key Decrypts ciphertext with the 3d key Decrypts output of first step with the 2 nd key Encrypts output of the first step with the 2 nd key Encrypts output of second step with the 3d key; gives the ciphertext to be sent Decrypts output of second step with the 1 st key; gives the original plaintext 168-Bit Encryption with Three 56-Bit Keys 1st 2nd 3rd 2nd 1st

17 17 Triple DES (3DES) SenderReceiver Encrypts plaintext with the 1 st key Decrypts ciphertext with the 1 st key Decrypts output with the 2 nd key Encrypts output with the 2 nd key Encrypts output with the 1 st key Decrypts output with the 1 st key 112-Bit Encryption With Two 56-Bit Keys 1st 2nd 1st 2nd 1st

18 18 Your knowledge about Cryptography 7) Based on the way DES and 3DES work, which of the following is true? a) 3DES requires more processing time than DES b) Compared 3DES, DES requires more RAM c) Both a and b 8) Given the increasing use of hand-held devices, 3DES will be more practical than DES. a)True b)False

19 19 Advanced Encryption Standard - AES Developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen, and submitted to the AES selection process under the name "Rijndael", a portmanteau of the names of the inventors Offers key lengths of 128 bit, 192 bit, and 256 bit Efficient in terms of processing power and RAM requirements compared to 3DES Can be used on a wide variety of devices including: Cellular phones PDAs Etc.

20 Asymmetric Key Encryption

21 21 Public Key Encryption For confidentiality Party A Party B Decrypt with Party A’s Private Key Encrypt with Party A’s Public Key Encrypt with Party B’s Public Key Decrypt with Party B’s Private Key Encrypted Message Encrypted Message Each Party uses other party’s public key for encryption Each Party uses own private key for decryption No need to exchange private key, but key needs to be very strong (512+ bit. Most today’s key are at least 1024 bit)

22 22 Public Key Encryption methods Asymmetric encryption methods are used both for Encryption in order to provide confidentiality Digital signature in order to provide partners’ authentication MethodsYear proposedComments RSA by Ron Rivest, Adi Shamir, and Leonard Adleman 19771995: First attack in lab conditions was reported Elliptic Curve Cryptosystem - ECC1985Becoming widely used Other symmetric encryption methods: Dieffe-Hellman, El-Gamal

23 23 Basic Terminology 3 Hashing: Mathematical process for converting inputs into fixed-length outputs Hash function: Algorithm that does the hashing. Uses an input + a shared secret or password. Example: Message Digest 5 (MD5), Secure Hash Algorithm (SHA). Hash: Fixed-length output of the hashing

24 24 Encryption Versus Hashing Encryption Uses a key as an input to an encryption method Output is similar in length to input Reversible; ciphertext can be decrypted back to plaintext Use of Key Length of Result Reversibility Hashing Password is usually added to text; the two are combined, and the combination is hashed Output is of a fixed short length, regardless of input One-way function; hash cannot be “de-hashed” back to the original string

25 MD5 (M essage -D igest algorithm 5) A widely used cryptographic hash function used to hash inputs (typed texts or files) in order to generate hash values (called checksums, message digest, or output) An MD5 hash value is typically expressed as a 16- hexadecimal number like 912df11644fccac439b6fc5f80af5cdb Each hex number is 8 bits MD5 generates a 128-bit hash value regardless of the input length. Commonly used to check the integrity of files like downloaded software programs 25

26 SHA1 (Secure Hash Algorithm 1) A widely used cryptographic hash function used to hash inputs (typed texts or files) in order to generate hash values (called checksums, message digest, or output) A SHA1 hash value is typically expressed as a 20-hexadecimal number like 79054025255fb1a26e4bc422aef54eb4 SHA1 generates a 160-bit hash value regardless of the input length Commonly used to check the integrity of files like downloaded software programs 26

27 Application Security: General apps &Web service

28 28 Applications and Buffer Overflow Buffer Overflow is the biggest issue in application coding Buffer overflow leads to Buffer Overflow Attacks Buffers are RAM areas where data is stored temporarily If an attacker sends more data than the programmer had allocated to a buffer, a buffer might overflow, overwriting an adjacent section of RAM RAM Buffer1Buffer2 Buffer7Buffer3Buffer4Buffer6Buffer5

29 29 Buffer Overflow Attack Occurs when ill-written programs allow data destined to a memory buffer to overwrite instructions in adjacent memory register that contains instructions. If the data contains malware, the malware could run and creates a DoS Example of input data: ABCDEF LET JOHN IN WITHOUT PASSWORD 29 BufferInstructions 123456 Print Run Program Accept input BufferInstructions 123456 ABCDEFLET JOHN IN WITHOUT PASSWORD Run Program Accept input

30 30 Stack entry: data buffer & Return address registry Stack Entry and Buffer Overflow Return Address 1. Write Return Address 2. Add Data to Buffer Data Buffer 5. Start of Attacker data 3. Direction of Data Writing 4. Overwrite Return Address When a program must put one subprogram on hold to call another, it writes the return address in RAM areas called stack entries The called subprogram may add data to the buffer to the point it overwrites the return address If the added buffer data is Attack code, this will be a buffer overflow attack http://www.metacafe.com/watch/1452134/buffer_overflow_attacks_explained_with_beer/

31 31 Preventing Buffer Overflow Use Language tools that provide automatic bounds checking such as Perl, Python, and Java instead lower level language (C, C++, Assembly, etc). However, this is usually not possible or practical because almost all modern OS are written in the C language. Eliminate The Use Of Flawed Library Functions like gets(), strcpy, and strcmp that fail to check the length or bounds of their arguments. Design And Build Security Within Code Use Source Code Scanning Tools. Example: PurifyPlus Software Suite can perform a dynamic analysis of Java, C, or C++ source code. // replace le following line Strcpy (buffer2, strng2); // by Strcpy (buffer2, string2, 8) For instance, this simple change informs strcpy() that it only has an eight byte destination buffer and that it must discontinue raw copy at eight bytes.

32 32 Web service security

33 33 Webservice & E-Commerce apps Web applications could be the target of many types of attacks like: Directory browsing Traversal attacks Web defacement Using HTTP proxy to manipulate interaction between client and server IIS IPP Buffer Overflow Browser attacks Time configuration

34 34 Web sites’ directory browsing If Directory Browsing is disabled on a web server: User cannot get access to list of files in the directory by knowing or guessing directory names

35 35 Directory browsing If Directory Browsing enabled on a web server: User can get access to the list of files in the directory by knowing or guessing directory names

36 36 Traversal Attack Normally, paths start at the WWW root directory Adding../ (Windows) or..\ (Unix) in an HTTP request might take the attacker up a level, out of the WWW root directory. Example: http://website.com../../ Example: http://castle.eiu.edu/~a_illia/BUS3500/Brief/Case1/../ If attacker traverses to Command Prompt directory in Windows 2000 or NT, he can execute any command with system privileges

37 37 IIS IPP Buffer Overflow The Internet Printing Protocol (IPP) service included in IIS 5.0 and earlier versions is vulnerable to buffer overflow and traversal attacks The jill.c program was developed to launch the attack using: GET NULL.printer HTTP/1.0 Host: 420-byte jill.c code to launch the command shell IIS server responds launching the command shell (C:\WINNT\SYSTEM32\>) giving the attacker SYSTEM privileges.

38 38 Browser Attacks Malicious links User must click on them to execute (but not always) Common file extensions are hidden by default in some operating systems.  attack.txt.exe seems to be attack.txt

39 39 Browser Attacks (Cont.) Common Attacks Redirection to unwanted webpage Scripts might change the registry, home page Some scripts might “trojanize” your DNS error- handling routine when you mistype a URL Pop-up windows Web bugs; i.e. links that are nearly invisible, can be used to track users at a website Domain names that are common misspellings of popular domain names  Microsoff.com, www.whitehouse.com (a porn site)www.whitehouse.com

40 40 Host Hardening

41 Computer Hardware & Software Computer Hardware Operating System Web service software (IIS, Apache,...) Web browser Productivity Software Client & server application programs

42 Your knowledge about Host hardening Which of the following is most likely to make a computer system unable to perform any kind of work or provide any service? a) Client application programs get hacked b) Server application programs (web service software, database service, network service, etc.) get hacked c) The operating system get hacked d) The connection to the network/Internet get shut down

43 OS market share OS Vulnerability test 2010 by omnired.com OS tested: Win XP, Win Server 2003, Win Vista Ultimate, Mac OS Classic, OS X 10.4 Server, OS X 10.4 Tiger FreeBSD 6.2, Solaris 10, Fedora Core 6, Slackware 11.0, Suse Enterprise 10, Ubuntu 6.10 Tools used to test vulnerabilities: Scanning tools (Track, Nessus) Network mapping (Nmap command) All host with OS installation defaults Results Microsoft's Windows and Apple's OS X are ripe with remotely accessible vulnerabilities and allow for executing malicious code The UNIX and Linux variants present a much more robust exterior to the outside Once patched, however, both Windows and Apple’s OS are secure.

44 Your knowledge about Host hardening You performed an Out-of-the-box installation of Windows XP and Linux FreeBSD 6.2 on two different computers. Which computer is more likely to be secure ? a) Windows XP b) Linux FreeBSD 6.2 c) They will have the same level of security What needs to be done, first, in order to prevent a hacker from taking over a server with OS installation defaults that has to be connected to the Internet? a) Lock the server room b) Configure the firewall to deny all inbound traffic to the server c) Download and install patches for known vulnerabilities

45 Security Baseline Because it’s easy to overlook something in the hardening process, businesses need to adopt a standard hardening methodology: standard security baseline Need to have different security baseline for different kind of host; i.e. Different security baselines for different OS and versions Different security baselines for different types of server applications (web service, email service, etc.) Different security baselines for different types of client applications.

46 Options for Security Baselines Organization could use different standards OS vendors’ baselines and tools e.g. Follow MS Installation procedure and use Microsoft Baseline Security Analyzer (MBSA) Standards Agencies baselines e.g. CobiT* Security Baseline Company’s own security baselines Security Baseline to be implemented by Server administrators known as systems admin * Control Objectives for Information and Related Technology

47 Elements of Hardening Physical security Secure installation and configuration Fix known vulnerabilities Remove/Turn off unnecessary services (applications) Harden all remaining applications Manage users and groups Manage access permissions For individual files and directories, assign access permissions to specific users and groups Back up the server regularly Advanced protections According toAccording to baselinebaseline

48 Example of Security Baseline for Win XP Clients OS Installation Create a single partition on HDD Format disk using NTFS file system Install Win XP and Service Pack 3 Fixing OS vulnerabilities Download and install latest patches Turn on Windows’ Automatic Updates checking Configure Windows Firewall Block incoming connections except KeyAccess and Remote Assistance Turn off unnecessary services Turn off Alerter, Network Dynamic Data Exchange, telnet Application Installation Centrally assign applications using group policies Fixing applications’ vulnerabilities Turn on each application’s automatic update checking

49 Hardening servers The 5 ‘P’ s of security and compliance: Proper Planning Prevents Poor Performance Plan the installation Identify The purpose of the server. Example: provides easy & fast access to Internet services The services provided on the server Network service software (client and server) The users or types of users of the server Determine Privileges for each category of users If and how users will authenticate How appropriate access rights will be enforced Which OS and server applications meet the requirements The security baseline(s) for installation & deployment Install, configure, and secure the OS according to the security baseline Install, configure, and secure server software according to sec. baseline Test the security Add network defences Monitor and Maintain

50 Hardening servers (cont.) Choose the OS that provides the following: Ability to restrict admin access (Administrator vs. Administrators) Granular control of data access Ability to disable services Ability to control executables Ability to log activities Host-based firewall Support for strong authentication and encryption Disable or remove unnecessary services or applications If no longer needed, remove rather than disable to prevent re-enabling Additional services increases the attack vector More services can increase host load and decrease performance Reducing services reduces logs and makes detection of intrusion easier

51 Hardening servers (cont.) Configure user authentication Remove or disable unnecessary accounts (e.g. Guest account) Change names and passwords for default accounts Disable inactive accounts Assign rights to groups not individual users Don't permit shared accounts if possible Configure time sync Enforce appropriate password policy Use 2-factor authentication when necessary Always use encrypted authentication

52 UNIX / Linux Hardening Many versions of UNIX No standards guideline for hardening User can select the user interface Graphic User Interface (GUI) Command-Line Interfaces (CLIs) or shells CLIs are case-sensitive with commands in lowercase except for file names

53 UNIX / Linux Hardening Three ways to start services Start a service manually (a) through the GUI, (b) by typing its name in the CLI, or (c) by executing a batch file that does so Using the inetd program to start services when requests come in from users Using the rc scripts to start services automatically at boot up Inetd = Internet daemon; i.e. a computer program that runs in the background

54 UNIX / Linux Hardening Program A Program B Program C Program D inetd Port 23 Program A Port 80 Program B Port 123 Program C Port 1510 Program D 1. Client Request To Port 123 4. Start and Process This Request 3. Program C 2. Port 123 /etc/inetd.config Starting services upon client requests Services not frequently used are dormant Requests do not go directly to the service Requests are sent to the inetd program which is started at server boot up

55 UNIX / Linux Hardening Turning On/Off unnecessary Services In UNIX Identifying services running at any moment ps command (process status), usually with –aux parameters, lists running programs  Shows process name and process ID (PID) netstat tells what services are running on what ports Turning Off Services In UNIX kill PID command is used to kill a particular process  kill 47 (If PID=47)

56 Advanced Server Hardening Techniques File Integrity Checker Creates snapshot of files: a hashed signature (message digest) for each file After an attack, compares post-hack signature with snapshot This allows systems administrator to determine which files were changed Tripwire is a file integrity checker for Linux/UNIX, Windows, etc.: www.tripwire.com ( ftp://coast.cs.purdue.edu/pub/tools/unix ) ftp://coast.cs.purdue.edu/pub/tools/unix

57 Advanced Server Hardening Techniques File 1 File 2 … Other Files in Policy List File 1 File 2 … Other Files in Policy List File 1 Signature File 2 Signature … File 1 Signature File 2 Signature … Tripwire 1. Earlier Time 2. After Attack Post-Attack Signatures 3. Comparison to Find Changed Files Reference Base File Integrity problem: many files change for legitimate reasons. So it is difficult to know which ones the attacker changed.

58 Other types of host that can be Hardened Internetwork Operating System (IOS) For Cisco Routers, Some Switches, Firewalls Even cable modems with web-based management interfaces

59 59 Which of the following is true about Application Security? If a server application (or service) is no longer needed, it should be turned off Fewer applications on a computer, fewer attack opportunities Use good security baselines to install and configure apps Do not install application centrally using group policies Add application layer authentication by requiring users to provide credentials to run application programs Implement cryptographic authentication for sensitive apps If a server application (or service) is no longer needed, it should be removed Do not turn on each applications’ automatic update checking


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