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“Blowfish”

1. It is indeed a restriction to the user to have a mandatory length of 16 ASCII characters for the input of the plaintext and 32 hex characters for the input of the ciphertext to the encryption and decryption respectively This was done though for display purposes and it does not mean that the algorithm cannot be used for longer inputs This is the reason why the Blowfish class is separate from the BlowfishProject class A developer can use the Blowfish class and run it to perform as long of inputs as he or she wants All in all the results were correct and the algorithm works despite the limitations of the software we created that wraps the class What We Learned First and foremost through this project we we re afforded the opportunity to explore another algorithm which was not presented in class In doing so we learned how Bruce Schneier was motivated to create a replacement for DES and also the theory behind creating this algorithm Unfortunately implementing this algorithm in java proved to be challenging For starters the java language does not support hex operations in an easy way like C and C As such we were forced to convert all of our plaintext to hexadecimal strings and then those strings had to be converted to integer in order to be XORed with the P box and S boxes using the Hex class we took from our professor s library In addition we learned that no cryptanalysis has been discovered for the Blowfish cipher Whil
2. Blowfish An implementation by Edward Wolf and Achilleas Tziaza Description The topic we investigated for our team project was Bruce Schneier s Blowfish cipher This cipher was proposed in December of 1993 and to this day no cryptanalysis has been discovered Even though this algorithm has been replaced with newer ciphers such as Twofish the Blowfish algorithm still remains a very simple and effective way to encrypt data When proposed the Blowfish algorithm was intended to replace DES because of its vulnerable 56 bit key length With the processing power of computers increasing 1t was possible that DES could become no longer secure Schneier s algorithm was aimed at providing a cipher that was capable of encrypting data with a key from 32 bits to 448 bits with the use of a key dependent S boxes and P box The purpose of this project was to demonstrate the practical application of this algorithm The software we developed demonstrated how a plaintext message can be encrypted using a 32 448 bit key or how an encrypted message can be decrypted Software Design Programming language When designing the software many approaches were taken into consideration Initially we looked into using Microsoft s C since it handles hex numbers in a much better way The conversion between integer and hex numbers was the main concern when selecting the programming language since the conversions are a vital part of the algorithm Converting
3. a hex number to an integer makes the use of exclusive or XOR much easier which is a part of the algorithm While deciding which language would fit our project the best we discovered a wide variety of tools in the RIT Computer Science Cryptography library by Dr Alan Kaminsky Using the class Hex java and its static methods that are described in http www cs rit edu ark cscl doc edu rit util Hex html we could easily convert a hex string to an integer and back to hex without any concerns This helped us conclude that our familiar programming language Java was the right approach The Algorithm Using the description of the algorithm found in the creator s Schneier s website and the resources found in the References section of this paper we developed the algorithm As a part of the algorithm are a P Box and four S Boxes The P Box 1s given by the creator whereas the S Boxes are created using the hexadecimal digits of the constant r For this implementation of the Blowfish algorithm the vectors for the S Boxes and the P Box were taken directly from Bruce Schneier s website This saves time when the algorithm is ran since the P Box and the S Boxes do not have to be created a process that is comparatively to the algorithm tedious The key that is used for Blowfish has a variable length from 32 bits up to 448 bits in 8 bit increments This implies flexibility in the strength of the algorithm The key is used in the follo
4. bits starting from the most significant bit MSB until the 32 bit are called L and the rest are called R which account as left and right as shown in Figure I below 32 bit Li 32 bit Ri Ee 32 bit Li 1 A we 32 bit Ri 1 a Figure 1 The feistel network Blowfish Encryption The left side is XORed with an integer from the P Box that has the same index It is then passed through the function F described later on and XORed with the right side of the 64 bit input Then the left and right chunks are flipped This happens 16 times On the 16 round there is no XOR ing happening The L and R are instead flipped Then the final L is XORed with the 17 index of the P Box and the final R is XORed with the 18 index of the P Box This new 64 bit output is the ciphertext and in the algorithm provided for this project is given in hex Since each hex number is 4 bits long the resulting ciphertext has a length of 16 hex characters The ciphertext along with the key can be later on used to decrypt the message The function F of the Blowfish algorithm is given by the following formula sBoxl aH sBox2 b 4sBox3 c sBox4 d where sBox1 sBox2 sBox3 and sBox4 are the four S Boxes and a b c d represent the 32 bit input to the function F chopped in four consecutive chunks of 8 bits each starting from the MSB in the following manner Figure 2 The input of the function F is divided into four 8 bit chunks The decryption i
5. ch in turn could reduce the code size and complexity However given the program s current implementation we could write a GUI that would show the encryption and decryption of a message using Blowfish fairly easily 11 References Schneier Bruce Description of a New Variable Length Key 64 Bit Block Cipher Blowfish Dec 1993 22 Mar 2008 lt http www schneier com paper blowfish fse html gt Schneier Bruce The Blowfish Encryption Algorithm One Year Later Schneier Sept 1995 22 Mar 2008 lt http www schneier com paper blowfish oneyear html gt Blowfish Encryption BletchleyPark 4 May 2008 lt http www bletchleypark net cryptology blowfish html gt Blowfish Cipher Wikipedia 3 Mar 2008 4 May 2008 lt http en wikipedia org wiki Blowfish_ cipher gt 12
6. e fact that the developer of this algorithm is recommending the adoption of Twofish it may not be worthwhile to spend time analyzing this problem One more improvement could happen in the error checking of the algorithm for example making sure that strings that should contain hexadecimal characters do indeed contain hexadecimal characters and that the input text in ASCII is of the pre defined size All the inputs to the Blowfish class are not checked for validity At least one Exception class that is part of the algorithm needs to be created to ensure that the proper information is given to the developer when using this implementation of Blowfish as part of a bigger software Also the Electronic Codebook Mode ECB is only used for display reasons and it is not supposed to be used in normal software because it leaks too much information about the plaintext This was of course used to display the fact that when an input string is longer than the default input defined by the algorithm encryption and decryption can still happen but in smaller chunks It is up to the developer to use other methods such as CBC mode or CFB mode etc Our purpose was to display the use of the Blowfish class in a wrapper class that processes the input and not to promote the use of ECB mode Lastly the program that we created was done using java We could implement the program in another language that is friendlier to bitwise operations and unsigned integers eg C whi
7. e the algorithm is still secure the developer still recommends that adopters move to his Twofish algorithm In building off of Blowfish s success Twofish uses 128 bit block encryption instead of 64 bit This adds additional security and is therefore more preferable to be implemented Lastly we learned about the applications of this algorithm Bruce Schneier s website lists over 150 different applications implementations of the algorithm After reading through the list we were fascinated to learn that this algorithm can be use in anything from file folder encryption to encrypting HTTP traffic 10 Possible Future Work The Blowfish algorithm uses key dependent S boxes and P box to encrypt data When the key is changed 521 operations are performed in order to generate the subkeys used in the algorithm In order to reduce the time of this generation a file containing all the subkey values could be created for each key This would reduce the amount of RAM and time needed in order to encrypt data It is possible that such a file could be loaded when the program parses its command line arguments In addition to increasing the algorithm s speed performing further cryptanalysis on this algorithm could yield additional vulnerabilities So far 4 rounds of the Blowfish algorithm are discoverable via a second order differential attack Further research would be necessary in order to discover more vulnerability to this algorithm However given th
8. n Blowfish is the exact same as the encryption with the only difference that the indices of the P Box are used in reverse order instead of looping from the first index to the 16 and then using indexes 17 and 18 to decrypt we loop from the 18 index to the 3 and then use the first and second for the final round The fact that the decryption is the same as the encryption but in reverse order makes the algorithm very easy to implement This sort of built in functionality of the algorithm was something we appreciated when coding the algorithm since we only had to figure out the encryption and then reverse the order of the loop and the indices to get the decryption Developer s Manual Using our implementation of the Blowfish algorithm is very easy Please follow the steps provided below e Once you download the jar file from our website you need to extract it in a folder The following files should appear in the folder o Blowrfish java the implementation of the algorithm o Hex java a class to manipulate hexadecimal numbers taken from the Computer Science Cryptography Library o BlowrfishProject java the main file you can run to test the algorithm e Navigate to that folder and use javac java to recompile and avoid using any previous versions of the class files that might have accidentally been included in the jar file For the developer we have included a UML diagram of the class that was created with instructions how t
9. o integrate this class in your own software development int pBox int sBoxi int sBox2 int sBox3 int sBox4 public Blowfish CString key public String encryptCString plaintxt public String decryptCString ciphertext private void xorKey private int functCString s Figure 3 UML diagram of Blowfish java A developer could easily use this simple class to incorporate the Blowfish algorithm by including the Blowfish java file as part of a bigger software platform The Blowfish constructor takes a key see key size in the description of the algorithm as a string of hexadecimal characters and then calls the xorKey function to XOR the key with the P Box and S Boxes This is done automatically and the developer does not need to worry about this part of the algorithm Once the key is instantiated there 1s no need to pass it when encrypting and decrypting If the main program remains loaded the key 1s stored in a private variable in the Blowfish class and cannot be accessed by anybody besides the Blowfish class itself A user can then send encrypt and decrypt requests to the software by calling the encrypt and decrypt functions Since the input is 64 bits if the input string is larger than that it can be divided into 64 bit pieces Each of the 64 bit inputs can be passed through the encryption function and the final ciphertext can be padded together to produce the resulting ciphertext The same can happen for the decrypti
10. on Once compiled the program can be executed by following the instructions specified in the User s Manual section of this report User s Manual After you compile the software using the instructions provided in the Developer s Manual use the following instruction to run the software e Type java BlowfishProject key plaintext or ciphertext e encrypt or d decrypt to encrypt or decrypt a message where o key 1s replaced with a 32 448 bit key given in hex in increments of one hex character 8 bits o plaintext or ciphertext is replaced with the paintext or the ciphertext depending on the operation the user would like to perform o e or d denote encryption or decryption Since the Blowfish algorithm encrypts only 64 bit blocks we used the Electronic Codebook mode to encrypt or decrypt the given plaintext or ciphertext The ECB mode simply divides the input into 64 bit chunks This way the resulting ciphertext or plaintext are e C E K P1 E K P2 e P D K C1 D K C2 o Where E denotes encryption P denotes decryption K is the key and P1 P2 C1 and C2 are the first two chunks of the input For simplicity reasons and in order to demonstrate that the encryption and decryption can be done in smaller chunks we only allow for an input of 16 ASCII characters for the plaintext 128 bits and an input of 32 hex characters for the ciphertext 128 bits This way two encryptions or two decryptions are happening and the
11. use of the algorithm is demonstrated more than once times Also the interface is currently in a command line mode Further improvements to the interface could be a graphical user interface Below is an example of the use of the software java BlowfishProject f4f3ffffffff EdWolfEdEdWolfEd e which means Encrypt the string EdWolfEdEdWolfEd with the given key ADO Terminal bash 80x24 Figure 4 Encryption As you can see here each round of the encryption is printed out and the final ciphertext is given at the end If we want to use the given ciphertext to decrypt it and receive back the plaintext we can use the following command java BlowfishProject f4f3ffffffff 7c59853b9c5e7e7f7c59853b9c5e7e7d d which means Decrypt the given ciphertext 7059853b9c5e7e7 7c59853b9c5e7e7F with the given key ANDO Terminal bash 80x24 Figure 5 Decryption As we can see the resulting text is our plaintext given back Results As shown in the previous section the software operates successfully We also tested the possibility of giving an incorrect key during encryption decryption which results to an incorrect output This means that our code is valid and that the Blowfish algorithm was implemented correctly Further tests included using incorrect sizes of the plaintext or ciphertext which yielded the program to not operate successfully and quit giving the user an error message that was informative
12. wing way e Take the first 32 bits of the key and XOR them with the first element of the P Box array Then take the next 32 bits and XOR them with the second element of the P Box array and so on and so forth If there are less than 32 bits remaining for the next item use the remaining bits and get the needed bits from the beginning of the key as if the key 1s really a circular string e Repeat this process for each S Box and the P Box This clearly implies that the bigger the key the fewer times the same parts of the key have to be used which in turn implies that the algorithm is even harder to break This is also the reason why the creation of the S Boxes and P Box were not included in the algorithm and were instead taken from the creator s website Since the key affects the S Boxes and P Box having them as constants inside the java class does not necessarily imply a security issue since they change according to the key Blowfish encrypts and decrypts 64 bit blocks This means that in terms of ASCH Blowfish can encrypt decrypt strings of length 8 Such strings are for example Ed Wolf which has a length of 8 characters ASCII Each ASCII character is represented as an 8 bit binary code which means that there are 64 bits in an ASCII string of 8 characters Such characters include exclamation marks and spaces To encrypt the 64 bits that are given as an input to the algorithm are separated to two 32 bit strings The first 32

“Blowfish”

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