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Homework #4: Basic Cryptography

Goal:

• Understand basic cipher and apply natural language statistics to decipher text encrypted using monoalphabetic cipher.
• Utilize OpenSSL aes command to encrypt and decrypt message.
• Understand RSA based encryption, authenticate, using simple example.
• Understand vulnerability of MD5 and the exploit scenario using stripwire created by Dan Kamisky.
• Understand about certificate creation, basic CA operation, secure web access with digital certifcates.

Assignment Date: 9/24/2008

Due Date: Parts 1-2 Due 10/1/2008; Parts 3-4 Due 10/8/2008; Part 5 Due 10/20/2008; Part 6 Due 10/10/2008

Description

Part 1: Understand basic cryptoanalysis and apply natural language statistics to decrypt a ciphertext. Document the process you use to analyze the encryption. Justify your answer by describing the various tests you perform to verify the results you obtained.

• Here is the ciphertext:

  HQCBCFDGDLJABEADLSFXARRCQQCCD
  FSDGCBBXLNCIRDSCHHBFJARUCHT
  FSDUACSAHBFJARABRCSELGHCCD
  FSDRCCOADDCQSCSAFGMFBFGLNCIRD
  HCQTABALHUASHLSHTAISDABEBCQHT
  
  
  HTASHCCOHTACHTAB,FGWIGHFGMFLB
  FSDTFJLSEYABTFYGHTAUAHHABNRFLK
  UANFIGALHQFGEBFGGXFSDQFSHADQAFB
  HTCIETFGMCBHTFHHTAYFGGLSEHTABA
  TFDQCBSHTAKBAFRRXFUCIHHTAGFKA
  
  
  FSDUCHTHTFHKCBSLSEAPIFRRXRFX
  LSRAFJAGSCGHAYTFDHBCDDASURFNO
  CTLOAYHHTAMLBGHMCBFSCHTABDFX
  XAHOSCQLSETCQQFXRAFDGCSHCQFX
  LDCIUHADLMLGTCIRDAJABNCKAUFNO
  
  
  LGTFRRUAHARRLSEHTLGQLHTFGLET
  GCKAQTABAFEAGFSDFEAGTASNA
  HQCBCFDGDLJABEADLSFQCCDFSDL
  LHCCOHTACSARAGGHBFJARADUX
  FSDHTFHTFGKFDAFRRHTADLMMABASNA
  

• Hint:
  • This is a poem with four quintain (five lines) stanzas. Line boundary helps locating starting and ending words.
  • Apply Ankur Patwa's character frequency tool to obtain the frequencies of uni-gram, di-gram, tri-gram in the ciphertext. Then try to generate a monalphabeic mapping using natural language statistics in viewgraph 10 of basic crypto. Normally we start by guessing the high frequency tri-grams as "the", "and". You can verify the correctness of the mapping by cross referencing among the tri-gram, di-gram, uni-gram, and also the starting words and ending words of a line.
  • Use Jeff Rupp's mono-alpha substitution tool, enter the cipher text and the current mapping we know. Once a potential word is deciphered, put space on the origintal text before and after the word. It will help tremedously in the following decrypt process.
  • Represent the plaintext and ciphertext in different cases or colors also help.
  • Here is a cryptoanalysis on another poem. http://cs.uccs.edu/~cs591/hw/example/hw4p1.html use example as username. Password to be announced in class.
• Document the key mappings, your observations, and intermediate cipher results.

Part 2: Encryption usign openssl with AES.

• An important hint of Part 1 is encrypted using OpenSSL with AES encryption and base 64 encoding. It is saved in http://cs.uccs.edu/~cs591/crypto/hw4Part1Hint.enc
• Decrypt the file with symmetric key (or called password/passphrase) cs591 and find out what it the hint. Give your best effort to solve the Part 1 before you try this hint.
• For the corresponding command see the above link. We are using 256 bit cbc (cipher block chaining) chaining mode.
• Question 2.1: Why we use base 64 encoding?
• Question 2.2: What are the benefit of using cbc?
• Question 2.3: Assume it takes exactly six seconds to run the decrypt command with a password on windom, and we know the password is a five letter word consisting of only alphanumerical characters (case matter here).
  • a. How long on average it will take to decript on windom by brute force (in terms of years)?
  • b. How do you know you have found the right password?

Part 3: Simple RSA-like encryption and authentication.

Repeat the RSA encipherment example for both Confidentiality and Authentication in page 35 of basic crypto viewgraph but apply Bob 's public key first followed by Alice private key. For example, the encipherment of 'H' will be (07^37 mod 77)^53 mod 77.

Show the enciphered values for H, E, L and D. Hint. You can use the bc program on CS Unix machines to compute the enciphered values as follows. First login to CS Unix machine. type "bc". The bc program then identifies itself (bc 1.06) and wait for your input of the expression. For the above encipherment equation. We enter (7^37 % 77)^53 % 77
the hit enter. The result will show in the next line. ^ represent "to the power" operation; % is the modulo operator.
Compare these values with those in the textbook example, what conclusion you can derive?
Repeat that for decipherment process by first applying Alice's public key then Bob's private key. Show the deciphered values for H, E, L and D.

Part 4: Vulnerability of MD5 and how it can be exploited.

• Read Wang et al and Kamisky's papers on MD5 vulnerability.
• Please login to bilbo or windom.uccs.edu to carry out this exercise. . If you run it on your own Linux machine, you can use "perl -MCPAN -e shell" then type "install Crypto::
• Copy the stripwire.tar.gz from cs591 account there with the following command:
  [bjardrey@athena ~]$ cp ~cs591/public_html/crypto/src/stripwire-1.1.tar.gz .
  [bjardrey@athena ~]$ tar xzvf stripwire-1.1.tar.gz
  stripwire-1.1/
  stripwire-1.1/backlash.pl
  stripwire-1.1/stripwire.pl
  [bjardrey@athena ~]$ cd stripwire-1.1
  [bjardrey@athena stripwire-1.1]$ dos2unix stripwire.pl
  The above dos2unix command convert the file to unix file format. Otherwise the shell will complain ": bad interpreter: No such file or directory".
  
• Then run the stripwire commands in the paper to generate two files with the same MD5 hash. Report what is the MD5 hash and SHA1 hashes generated.
  • ./stripwire.pl -v -b backlash.pl
  • diff fire.bin ice.bin
  • ./stripwire.pl -v -r ice.bin (failed unable to decrypt file)
  • ./stripwire.pl -v -r fire.bin & (should succeed and run backlash.pl on backgournd listen to 50023)
  • telnet 127.0.0.1 50023 (or telnet bilbo 50023 from another machine)
  • you should see
    Trying 127.0.0.1...
    Connected to 127.0.0.1.
    Escape character is ’ˆ]’.
  • You can then enter any command on this backdoor such as
    cat /etc/ssh/ssh_config
  • To conclude the telnet session type control-] (^]).
  • Note you should terminate the backlash.pl that is running on the background, by entering fg as command followed by control-C to kill that process.
    
• run the stripwire command to decrypt the file and run the command (backlash.pl) attached.
• use telnet 127.0.0.1 50023 to connect to the remote shell and run "cat backlash.pl" or "ls".
• Answer the following questions:
  • Q4.1. What are the MD5 and SHA1 hashes generated? Are they different from those in the paper?.
  • Q4.2. What formula is the base of Kamisky's implementation that can generate two files with arbitary length and same MD5 hash?
  • Q4.3. What is the block size of MD5? What is the length of SHA1 hash?

Part 5: Sign Server/Client Certificates and Setup Apache Web Server with mutual authentication using digital certificates.

• Repeat the steps in http://cs.uccs.edu/~cs591/secureWebAccess/secureWebAccess.htm for CA certificate signing and client/sever certificate request generation and signing.
• Note that we will use fc9 instead of fc4 and use Firefox browser instead of IE
• For the web server, use the domain name <yourlogin>.csnet.uccs.edu that was created for you.
• For the client certficates, create one for you and one for the cs591. Export them as .p12 files and install them in a Firefox browser either in the EN138 lab or your own PC.
• With the designated IP address and legitimate Domain name, you can access the web server securely through UCCS VPN.
• Use the fc9 virtual machine in your public_html/vmware directory. Use username csnet to login. The password and root password will be announced in class.
• Change fc9 vm name to <your login>fc9.
• Once start the fc9, you should
  • Start a terminal window by selecting Applications | System Tools | Terminal
  • switch to super user with "su -"
  • change the IP address to your designated IP address in http://cs.uccs.edu/~cs591/hw2F2008.html logistic section.
    for ecample Chris Eberle, should chagne its fc9 vm eth0 address to 128.198.61.43
    using
    ifconfig eth0 128.198.61.43 netmask 255.255.255.128
    route add default gw 128.198.61.1
  • change the hostname to <your ufp account without trailing #>.
  • two DNS entries were created for you <your ufp account without trailing #>.csnet.uccs.edu and <your ufp account without trailing #>2.csnet.uccs.edu on gandalf.uccs.edu (CSNET DNS server)
• Generate snapshots of server certificate and client certificate-based access as shown in the secure web access web page.
• Save the snapshot image files in your cs591 web page and email me just the urls.
  
• To spread the load, we will divide into two-person groups and some of the group will use walden, walrus, wind, and sis. For those groups not using the bilbo, I have copied the fc9 vm your directory in D:\work\cs591\F2008\<login>
  
  

  Group	Name	External IP addresses	Designated Host for vm
  1	Anderson, Christopher Alan	128.198.61.37-38	bilbo
  	Branch, Charles Thomas	128.198.61.39-40
  2	Brunner, Andrea Marie	128.198.61.41-42	bilbo
  	Eberle, Christopher James	128.198.61.43-44
  3	Edokpayi, Idaho Omoviro	128.198.61.45-46	bilbo
  	Godavari, Ganesh Kumar	128.198.61.47-48
  4	Greene, Michael Richard	128.198.61.49-50	bilbo
  	Johnson, Raoul Christopher	128.198.61.51-52
  5	Kidder, Jeffrey Lynn	128.198.61.53-54	bilbo
  	Miller, Jeffrey Wayne	128.198.61.55-56
  6	Mohsen, Fadi Fuad	128.198.61.57-58	bilbo
  	Nguyen, Hoang Huy	128.198.61.59-60
  7	Reddy, Sreedeepti	128.198.61.63-64	walden
  	Ruiz, Daniel Alfonso	128.198.61.65-66
  8	Sundquist, Nadine Dominique	128.198.61.67-68	wind
  	Taylor, Joe Bert	128.198.61.69-70
  9	Thomas, Ryan Matthew	128.198.61.71-72	walrus
  	Tran, Kim-lan Lim	128.198.61.73-74
  10	White, Richard Lee	128.198.61.75-76	sis
  	Hamann, Ronald William	128.198.61.83-84
  11	Florentino, Gustavo H	128.198.61.85-86	bilbo
  	Chow, Edward	128.198.61.77-78

Part 6. Prepare client certificate for midterm secure access.

• Submit certificate request.

  Please submit youir certificate request to me by Friday night,  I will return the signed certificate by Saturday night and give you chance to access the secure web site, which will host midterm page, on Athena.uccs.edu before our class next Monday. Please use your ufp account as Common Name and uccs email address for Email.

  Login to Bilbo
  cd public_html
  /etc/pki/tls/misc/CA –newreq
  mv newreq.pem csnetReq.pem
  mail -s "sign request" chow@eas.uccs.edu < csnetReq.pem
  mv newkey.pem csnetKey.pem

• Edward sign certficate.
  
  After receiving your certificate request, I will sign it on athena, leave a copy in http://cs.ucccs.edu/~cs591/crypto/ca, and return the signed certificate in an email.
• Generate .p12 file and import to firefox browser
  
  Assume your login name is csnet, here are the steps to create the .p12 file with your client certificate and private key for accessing secure web page on Athena.uccs.edu:
  • After receiving my email with csnetCert.pem as attachment, run the following command:
    openssl pkcs12 -export -in csnetCert.pem -inkey csnetKey.pem -out csnetClient.p12
  • Download the csnetClient.p12  to the PC you would like to use to access the midterm web page
  • Import csnetClient.p12 file as your client certificate to firefox
    • Start firefox
    • Select Tools | Options
    • Select Advanced  | Encryption tab  then hit the “View Certificate” button
    • Select Your Certificates  tab then hit “Import” button
    • Select the csnetClient.p12 file  to import the certificate
  • Type https://athena.uccs.edu/secure/ to see if you can access the secure web page there.
    When prompt for selecting the certificate make sure you select the one just imported.
    If you were ask to enter username or password, then the certificate you selected is wrong.