CSreport_lab1_DianYu&QiangHuang

Course: DT5721Instructors: Fredrik Jönsson Distributed Systems and SecurityLaboratory 1: DESLab Group: 1Dian Yu, Qiang HuangLaboratory Date: Nov 30, 2010Approved by ___________Date: ___________Contents1. Introduction 32. Results of Running Example Program 4 2.1 Program function and related concepts 42.2 Running results 63. Program Development and Running Result 7 3.1 Program development 7 3.2 Running results 9 Appendix 101.IntroductionThe Data Encryption Standard (DES) is a block cipher that uses shared secret encryption. It was selected by the National Bureau of Standards as an official Federal Information Processing Standard (FIPS) for the United States in 1976 and which has subsequently enjoyed widespread use internationally. It is based on a symmetric-key algorithm that uses a 56-bit key. The algorithm was initially controversial with classified design elements, a relatively short key length, and suspicions about a National Security Agency (NSA) backdoor. DES consequently came under intense academic scrutiny which motivated the modern understanding of block ciphers and their cryptanalysis.2.Results of Running Example ProgramThis chapter will discuss concepts relating with the example program, and also the result.2.1 Program functions and related conceptsFigure 1 shows how the DES works, A block to be enciphered is subjected to an initial permutation IP, then to a complex key-dependent computation and finally to a permutation which is the inverse of the initial permutation IP-1.The 64 bits of the input block to be enciphered are first subjected to the following permutation, called the initial permutation IP:That is the permuted input has bit 58 of the input as its first bit, bit 50 as its second bit, and so on with bit 7 as its last bit. The permuted input block is then the input to a complex key-dependent computation described below. The output of that computation, called the preoutput, is then subjected to the following permutation which is the inverse of the initial permutation:Let the 64 bits of the input block to an iteration consist of a 32 bit block L followed by a 32 bit block R. Using the notation defined in the introduction, the input block is then LR.Let K be a block of 48 bits chosen from the 64-bit key. Then the output L'R' of an iteration with input LR is defined by:L' = RR' = L ○+ f(R,K)With more notation we can describe the iterations of the computation in more detail. Let KS be function which takes an integer n in the range from 1 to 16 and a 64-bit block KEY as input and yields as output a 48-bit block Kn which is a permuted selection of bits from KEY. That isKn = KS(n,KEY)2.2 Running resultsThe result of the example program is showed below.3.Program Development and Running ResultThis chapter will show the development of the example program, and also the result.3.1 Program developmentAs the requirement, what we need to do is to complete the encryption, decryption and the F function party in the example code.EncryptionAs following the description, at first, The 64 bits of the input block to be enciphered are first subjected to the initial permutation (IP).applyIP(plaintext,ciphertext); //start by apply IPThe calculation of f(R,K), put the output at TempData2F(RTemp, roundKeys[r], TempData2);and then, perform an bitwise xor operation between the left part (LTemp) and the TempData2.TempData2[0] = TempData2[0] ^ *LTemp;TempData2[1] = TempData2[1] ^ *(LTemp+1);TempData2[2] = TempData2[2] ^ *(LTemp+2);TempData2[3] = TempData2[3] ^ *(LTemp+3);At last, exchange the left and right part.memcpy(LTemp, RTemp, 4);memcpy(RTemp, TempData2, 4); //update R and LDo the same work 16 times.for(r=1;r<=16;r++)apply inverse IPapplyInvIP(TempData , ciphertext);DecryptionThe only difference from encryption is K16 is used in the first iteration, K15 in the second, and so on, with K1 used in the 16th iteration.So, we just need to let roundKeys[16] to calculate with RTemp at first when doingt the 16 iterations.for(r=1;r<=16;r++){//call F, use correct roundKeyF(RTemp, roundKeys[17-r], TempData2);F functionA sketch of the calculation of f(R,K) is given in Figure 2.Let E denote a function which takes a block of 32 bits as input and yields a block of 48 bits as output. Let E be such that the 48 bits of its output, written as 8 blocks of 6 bits each, are obtained by selecting the bits in its inputs in order according to the following table:So, according to this, the function below is uesd for expand the input to 48 bit. applyE(R, ExpandArea); //expand R to 48-bitsand then, perform an bitwise xor operation between the ExpanArea and the sub-key(roundKeys[i]).for(i = 0; i < 6; i++){ExpandArea[i] = ExpandArea[i] ^ *(roundKey+i); //xor with roundKey }The output of the xor will have a complicated calculation with Sbox, here, we just need to call the function named SBox() which has already defined before.SBox(ExpandArea, TempOut); //call SBoxThe result is 48 bit, so we need use pbox to transform it to 32 bitapplyP(TempOut, output); //call final permutation3.2 Running resultsThe result of the program about encryption and decryption is showed below.AppendixPart of Code(which is modified by ourselves): des.c/*--------------YOU SHOULD IMPLEMENT encrypt, decrypt, and F ----------*/ byte* encrypt(byte* plaintext,byte** roundKeys){/*encrypt plaintext, using the roundKeys*/byte* ciphertext;int r; //Loop Variable to Keep track of Roundschar TempData[8];char TempData2[4];char *LTemp = TempData; /* left 4 bytes (half) of the data block. */char *RTemp = &(TempData[4]); /* right half of the ciphertext block. */ //allocate memory for ciphertextciphertext=calloc(8,sizeof(byte));if( NULL == ciphertext){printf("Memory Allocation Failed \n");return NULL;}//start by apply IPapplyIP(plaintext,ciphertext);//initiate L and Rmemcpy(TempData, ciphertext, 8);//iterate 16 rounds in DESfor(r=1;r<=16;r++){//call F, use correct roundKeyF(RTemp, roundKeys[r], TempData2);//xor with LTempData2[0] = TempData2[0] ^ *LTemp;TempData2[1] = TempData2[1] ^ *(LTemp+1);TempData2[2] = TempData2[2] ^ *(LTemp+2);TempData2[3] = TempData2[3] ^ *(LTemp+3);//update R and Lmemcpy(LTemp, RTemp, 4);memcpy(RTemp, TempData2, 4);}TempData2[0] = TempData[0];TempData2[1] = TempData[1];TempData2[2] = TempData[2];TempData2[3] = TempData[3];TempData[0] = TempData[4];TempData[1] = TempData[5];TempData[2] = TempData[6];TempData[3] = TempData[7];TempData[4] = TempData2[0];TempData[5] = TempData2[1];TempData[6] = TempData2[2];TempData[7] = TempData2[3];//apply inverse IPapplyInvIP(TempData , ciphertext);return ciphertext;}byte* decrypt(byte* ciphertext,byte** roundKeys){/*decrypts plaintext, using the roundKeys*/byte* plaintext;int r;char TempData[8];char TempData2[4];char *LTemp = TempData; /* left 4 bytes (half) of the data block. */ char *RTemp = &(TempData[4]); /* right half of the ciphertext block. */ //allocate memory for plaintextplaintext=calloc(8,sizeof(byte));//start by apply IPapplyIP(ciphertext,plaintext);//initiate L and Rmemcpy(TempData, plaintext, 8);//iterate 16 roundsfor(r=1;r<=16;r++){//call F, use correct roundKeyF(RTemp, roundKeys[17-r], TempData2);//xor with LTempData2[0] = TempData2[0] ^ *LTemp;TempData2[1] = TempData2[1] ^ *(LTemp+1);TempData2[2] = TempData2[2] ^ *(LTemp+2);TempData2[3] = TempData2[3] ^ *(LTemp+3);//update R and Lmemcpy(LTemp, RTemp, 4);memcpy(RTemp, TempData2, 4);}TempData2[0] = TempData[0];TempData2[1] = TempData[1];TempData2[2] = TempData[2];TempData2[3] = TempData[3];TempData[0] = TempData[4];TempData[1] = TempData[5];TempData[2] = TempData[6];TempData[3] = TempData[7];TempData[4] = TempData2[0];TempData[5] = TempData2[1];TempData[6] = TempData2[2];TempData[7] = TempData2[3];//apply inverse IPapplyInvIP(TempData , plaintext);return plaintext;}void F(byte* R,byte* roundKey,byte* output){/*The function F in DES */byte ExpandArea[6];byte TempOut[8];int i;//expand R to 48-bitsapplyE(R, ExpandArea);//xor with roundKeyfor(i = 0; i < 6; i++){ExpandArea[i] = ExpandArea[i] ^ *(roundKey+i);}//call SBoxSBox(ExpandArea, TempOut);//call final permutationapplyP(TempOut, output);}/*-----YOU DO NOT NEED TO MODIFY THE FOLLOWING METHODS--------*/。