Lab 01: git'em done

Submission instructions for labs can be found on the resource pages. In paticular, you should view this subsection: Creating a new branch and submitting

Description

• You will perform basic git commands to fork/clone/push

Preliminaries

• This assignment can be completed on any machine
• gitlab repository:

  http://saddleback.academy.usna.edu/aviv/lab-1.1
  

Instructions

• Fork and clone the assignment repository
• Update a json file: fill-me-in.json
• Create a new json file called current-temp.json that has the following fields:

  Location : current location (type string)
  Timestamp : seconds since epoch (type number) 
  GPS : gps coordinates of weather readong (type string)
  temp : temperature in celsiusm (type number)
  

• Submit all work to gitlab

Submission Requirements

• fill-me-in.json : json you fill in
• current-temp.json : new json you create

Description

• You will write a c program to brute force an encrypted message

Preliminaries

• This assignment can be completed on any machine but will require access to a course VM running on saddleback at port 2222

  ssh -p 2222 [email protected]
  

• gitlab repository:

  http://saddleback.academy.usna.edu/aviv/lab-1.2
  

Instructions

• fork and clone the assignment repository
• ssh into the course VM from a machine with a registered public key in gitlab.

  ssh -p 2222 [email protected]
  

• On the VM Execute the following binary to retrieve your secret encrypted message:

  ~aviv/lab/01.2/get_secret
  

• The output is an string hex of an encrypte secret message that was encrypted with the following code:

  //Encryption Routine
  unsigned short iv =  0xcafe;
  for(i=0; i < len ; i+=2){
    unsigned short * seg = (unsigned short *) &buffer[i];
    *seg = *seg ^ key ^ iv;
    iv = *seg;
  }
  

• Your task is to crack the encryption by determining the key and decrypting the message
• You must do this by creating a C-program named: cracker.c
• You must also provide a Makefile to compile your program
• Once you have cracked the message fill in the json file called solution.json with the following fields:

  key : two byte hex string for key (type string formated like "\xca\xfe")
  msg : the decrypted message (type string)
  

Submission Requirements

• Makefile : Makefile to compile cracker.c
• cracker.c : cracker.c code for cracking the inpput
• solution.json : json file with secret information

Hints

• Why not brute force … only two byte keys?
• How can you check if message is in ASCII? Have you checked out an ASCII table recently? http://www.asciitable.com/

Description

• Using the key cracked from the previous part, write an encryption routine to encrypt a new message

Preliminaries

• This assignment can be completed on any machine
• gitlab repository:

  http://saddleback.academy.usna.edu/aviv/lab-1.3
  

Instructions

• Fork and clone the repository
• Write a c-program named encyrpt.c that will encrypt a message using the following routine (in pseudo code)

  key := command_line_argument[1]  ; must be at most a 2-byte number
  IV  := command_line_argument[2]  ; must be at most a 2-byte number
  msg := command_line_argument[3]  
  
  cipher_text := [] ; /empty list/
  
  if len(msg) % 2 == 1: ; len(msg) should include entire message, with NULL bytes
     msg = msg|'\0'     ; round message length up to nearest 2-byte
  
  i := 0
  while i < len(msg){   ; len(msg) should include entire message, with NULL bytes
                        ; e.g., strlen(msg)+1
     m1 := msg[i]
     m2 := msg[i+1]
  
     plain_block = m2|m1    ; single bytes concatenated to form 2-byte block
                            ; note the order of byte is reversed
  
     cipher_block := plain_block ^ key ^ IV  ; encrypt with xor
  
     cipher_text := cipher_text|cipher_block ; concatenate cipher_block 
                                            ; on the cipher_text
  
     IV := cipher_block
     i := i+2
  }
  
  output to stdout: cipher_text as hex encoded string
  

• Complete the json file solution.json with the following fields all of which you can choose, but the encrypted message should be based on the output of your program:

  key : hex encoding of a key  (type string)
  IV  : hex encoding of an IV (type string)
  msg : plain text message  (type string)
  enc : encrypted message (type string)
  

• You are required to submit a Makefile to compile your program
• You will also find a compiled executable decrypt that you can use to test your output. Here's the -h output fo that program:

  user@si485H-base:1.3$ ./decrypt -h
  USAGE: ./decrypt key iv msg msg_len
  
  key     : hex value for the key, e.g  "0xffff"
  IV      : hex value for the IV, e.g., "0xffff"
  msg     : the message to be decrypted
  msg_len : the length of the message (in case it contains NULL)
  

Sample Usage

• Here's what your output for encrypt should look like:

  aviv@si485H-saddleback:1.3$ ./encrypt "0xffff" "0xbbbb" "Hello World!"
  key: 0xffff IV:0xbbbb
  msg: "Hello World!"
  msg_len: 14
  \x21\xc\xb2\x9f\x6d\xf\xfd\xa7\x6e\x2a\xb0\xb1\x4f\x4e
  

• Here's that message decyrpted with the provided decrypt function

  user@si485H-base:1.3$ ./decrypt "0xffff" "0xbbbb" $(printf "\x21\xc\xb2\x9f\x6d\xf\xfd\xa7\x6e\x2a\xb0\xb1\x4f\x4e") 14
  key: 0xffff IV:0xbbbb
  msg: "\x21\xc\xb2\x9f\x6d\xf\xfd\xa7\x6e\x2a\xb0\xb1\x4f\x4e"
  msg_len: 14
  Hello World!
  

Submission Requirements

• Makefile : Makefile to compile encrypt.c
• encrypt.c : source code for encryption routine
• submission.json : submission information as json

Hints

• pointer casting can really help, say casting a short * to char *.
• Remember your bit-wise operators:
  • & : bit-wise and
  • | : bit-wise or
  • ^ : bit-wise xor
  • << : left shift
  • >> : right shift