Programming Assignment 3: Salted Password

1. Introduction

In this programming assignment, you will try to recover a password from a hash value. In the Lecture 26 (Slides

No. 7-9) we have discussed the concept of password salt. The salted password (i.e. password with a salt attached)

can greatly increase the search space for dictionary attack. In this assignment, you will conduct a dictionary attack

only knowing hash value of salted password. In other word, you will guess or recover a password given a hash

value of a salted password. To simply the guessing process, we provide a password file, which only contains 100

passwords, where each password has merely 6 uppercase letters (please refer to password.txt). Note in reality at

least 500,000 common passwords should be used in an attack.

Since normally passwords are stored as hash values, the common way to conduct a dictionary attack is to hash

every password in the password file and store the hash value. Whenever we obtain a hash value, we can compare

this value against the hash values in the file. If we find a match, we would know which password the hash value

corresponds to. Then the password is recovered. In our case, for a file with only 100 passwords, only 100 hash

values would be generated. It is very easy to search 100 hash values. To increase the difficulty of dictionary

attack, password salt is introduced. The salt is a random value that we attach to a plaintext password. The hash

value is calculated on the salted password (i.e. H(salt | password)). The salt (i.e. the random value) adds the

uncertainty to the password. For each password, the number of possible hash values is equivalent to the number of

possible combinations of salt.

In this assignment, you will use a three-digit salt. This means the salt is a decimal number and each digit can be

one of 10 possible numbers, namely 0-9. Since a salt has three digits, the number of all possible salt values is

10x10x10=1000. For one password, there are 1000 possible hash values. For a file of 100 passwords, the total

hash values are 100x1000=100,000. In other words, the search space for the dictionary attack is 100,000. One

way to conduct the dictionary attack for the salted password is to attach every possible salt to a password and then

hash the salted password (i.e. password with salt attached). Then we store all the hash values in a dictionary file.

When we obtain a hash value for an unknown password, we search this value in the dictionary file. If we find a

match, then the password is recovered (since the dictionary file should list which password the hash value

corresponds to). With the salt, the size of the dictionary file increases 1000 times in this example.

As mentioned above, each password has 6 uppercase letters. To calculate hash, those letters would be converted to

numeric values. Here we use ASCII value to represent a letter. ASCII values are widely used in computer to store

character. The ASCII table can be found at

https://www.asciitable.com/. The uppercase letters have values

ranging from 65 to 90. If a password is DEIKAE, you would first lay out the ASCII value of every letter side by

side. So for the password of DEIKAE, you would generate 686973756569. Then you would insert the salt in front

of this number sequence. For example, if a salt is 109, you would generate 109686973756569. Then apply the

following hash function to this number sequence

Hash function = ( (

243

x left ) + right ) %

85767489

Where, left is the left 8 digits of the number sequence. In this example, it is 10968697, which is treated as a long

integer number. And right is the rest 7 digits of the number sequence. In this example. it is 3756569, which is

treated as a long integer number.

The result of the hash function is the hash value for this salted password. If we want to generate all possible hash

values for this password, we need attach all possible values of salt to the password one by one. For the password

DEIKAE (whose ASCII string is 686973756569). We should have 1000 salted password possibilities for this

password as shown below. Then the hash values for those 1000 salted passwords will be stored in the dictionary

file.

2. Implementation

2.1. Inputs

As mentioned above, we will provide a password file, which contains 100 passwords. Your program will ask the

user to enter the name of the password file. For the user input, you can use scanf (in C programming) or Scanner

class (in Java) or anything equivalent. Then the program will ask the user to enter a hash value. Your program

will try to recover the password based on this hash value. Note this value should be treated as long integer.

2.2. Dictionary File

Based on the input password file, you will generate a dictionary file which contains all possible hash values for all

password. As mentioned above, for each password the possible hash values are 1000. Therefore, the dictionary

file will have 100 x 1000 = 100,000 entries. Your program will save all entries in a text file. You are required to

generate this text file. The entries of this dictionary file has the following format: [password salt hash_value]. For

example, the first few entries of dictionary file should be similar to the following:

XEGUOQ 000 23411352

XEGUOQ 001 47711352

XEGUOQ 002 72011352

XEGUOQ 003 10543863

XEGUOQ 004 34843863

2.3. Outputs

Once the user enters the name of password file, your program can generate the dictionary file as described above.

Now given a hash value, you can recover password by matching the given hash value to one of the hash values in

the dictionary file. You will ask the user to enter a hash value as the target hash value. Then you program searches

the dictionary file for this value. If a match was found, your program should print out indication that the password

is recovered. Then the program should print out the recovered password (which is the password corresponds to

the hash value) and the number of entries has been searched. If the user-entered hash value does not match any

hash value in the dictionary file. You should also print out a line indicating the password is not found and number

of entries has been searched. In this case, the number of entries searched should be 100,000.

000 686973756569

001 686973756569

002 686973756569

003 686973756569

. . . . . .

009 686973756569

010 686973756569

011 686973756569

. . . . . .

998 686973756569

999 686973756569

2.4. Long Integer

Since this assignment involves concatenating numbers, some of the numbers are too big to be stored in int.

When your program calculates hash function or prompt the user to enter hash value, please remember using

long to store the values.

2.5. Procedure

The basic procedure and requirements for this assignment are listed below:

Step 1: Prompt the user to enter the name of password file

Step 2: Generate the dictionary file

Create a dictionary file and for each password

Step 2.1: Generate all possible 3-digit salt

Step 2.2: Attach each salt to the password

Step 2.3: Calculate hash value using the hash function

Step 2.4: Write password, salt and hash value to the file

Step 2.5: Repeat Step 2.2-2.4 for all salts

Step 2.6: Repeat Step 2.1-2.5 for all passwords

Step 3: Prompt the user to enter a hash value.

Step 4: Search the dictionary file for a match of this value. If a match is found, print out a success message

and show the recovered password, salt value and number of entries have been searched. If no match is found,

print out a failure message and show the number of entries haven been searched.

3. Submission

Your source codes should be included in one file. You are required to comment your codes to help TAs understand

your process. You will also generate a report to describe your programs briefly and explain how to compile/run

your program on Eustis. Your report should include the screenshots to show the output results. For verification,

you should include screenshots for at least one successful case and one failure case. You will zip the source code

file and report in one file. Since your program will generate the dictionary file in the process, you do not need to

submit the dictionary file. You will submit the zip file through Webcourses. As discussed before, you may submit

multiple versions before deadline. So submit early. Only the last version before the deadline would be graded. The

late submission will receive penalty of 1 point per minute past the deadline.

Password.txt file

XEGUOQ WBBIPR FGCOGM JSAXZZ BREUGV LKKNQC JDSXBH HPUDCR VPDZRA DBOIYR WFJRFV EOZQMH QXMCIF TNPLVF DBNSSS TKINZI SUASHU FGDNVG VSDIFC IXKPLI MANVLO YOASRW SEBYLP SASQCZ HJDQEG VHVGSG OAIOQM BHRWVD YJVKGH GYCYUV ZEKAQU NKAHNQ NXEALY ZKDZWY PINARQ NJSKCK IOJOCO OSIGZA TIWNVG UPQIUC PAQUNN XTTMAZ RGRSST DHFGQM UCBAOM SZABIW UYROHE WAYIXM ZWZHVF IZSCVQ CWDXLK YDHJFC TORTOD VTBMUX HJDARK JYCORX DYUFNS JTFBFG QNXONG NWATEF QSLUNU TIHZMB JUOZTB PBOQKZ KBHKHI KBRBQP PLUPPS TXLANP PKBAYQ HKDJNH BASSAT VESYMF GQVMRN MODNJQ QXJHVO JWJBGK QQPROB RVBCAV OOVQQL NHQAEF GDMZRP AXRFNA LCMWJA XLFYQZ CEPAUM OPYGFE YVZAZJ ARPOKP TYHOKU JCDVQX TDHGAW UWJXLZ JOAWHN MPGBKY MKGVCW RHLGBU YNWZUP ECSICR IYNGNC ZFXOML