Data Encryption Standard DES Most widely used block
Data Encryption Standard (DES) • Most widely used block cipher in the world • Adopted in 1977 by NIST – as FIPS PUB 46 • Encrypts 64 -bit data using 56 -bit key • Has widespread use • Has been considerable controversy over its security
DES Encryption
Initial Permutation: IP • • • First step of the data computation IP reorders the input data bits Even bits to LH half, odd bits to RH half Has quite regular structure (easy in h/w) Example: IP(675 a 6967 5 e 5 a 6 b 5 a) = (ffb 2194 d 004 df 6 fb)
Permutation Tables for DES
![Initial Permutation unsigned char IP[]={ 58, 50, 42, 34, 26, 18, 10, 2, 60,](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-5.jpg "Initial Permutation unsigned char IP[]={ 58, 50, 42, 34, 26, 18, 10, 2, 60,")
Initial Permutation unsigned char IP[]={ 58, 50, 42, 34, 26, 18, 10, 2, 60, 52, 44, 36, 28, 20, 12, 4, 62, 54, 46, 38, 30, 22, 14, 6, 64, 56, 48, 40, 32, 24, 16, 8, 57, 49, 41, 33, 25, 17, 9, 1, 59, 51, 43, 35, 27, 19, 11, 3, 61, 53, 45, 37, 29, 21, 13, 5, 63, 55, 47, 39, 31, 23, 15, 7 }; Data[1] Data[0] Initial Permutation New. Data[1] New. Data[0]
![Initial Permutation Data[1] Data[0] 1 2 3 4 5 6 7 8 9 10](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-6.jpg "Initial Permutation Data[1] Data[0] 1 2 3 4 5 6 7 8 9 10")
Initial Permutation Data[1] Data[0] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 New. Data[1] New. Data[0]
Initial Permutation Initial. Permutation(unsigned long *Data) { DWORD tmp. Mask; DWORD set. Mask; DWORD New. Data[2]={0, }; for(int i = 31 ; i >= 0 ; i--) { tmp. Mask = 0 x 00000001; set. Mask = 0 x 00000001<<(31 -i); if((IP[i] <= 32) && (Data[1] & (tmp. Mask << (32 -IP[i])))){ New. Data[1] = New. Data[1] | set. Mask; }else if((IP[i] > 32) && (Data[0] & (tmp. Mask << (64 -IP[i])))){ New. Data[1] = New. Data[1] | set. Mask; } } Newdata (index 31 to 0)
Initial Permutation for(i = 63 ; i >=32 ; i--) { tmp. Mask = 0 x 00000001; set. Mask = 0 x 00000001<<(63 -i); if((IP[i] <= 32) && (Data[1] & (tmp. Mask << (32 -IP[i])))){ New. Data[0] = New. Data[0] | set. Mask; }else if((IP[i] > 32) && (Data[0] & (tmp. Mask << (64 -IP[i])))){ New. Data[0] = New. Data[0] | set. Mask; } } Data[1] = New. Data[1]; Data[0] = New. Data[0]; } Newdata (index 63 to 32)
![Inverse Initial Permutation unsigned char IIP[]={ 40, 8, 48, 16, 56, 24, 64, 32,](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-9.jpg "Inverse Initial Permutation unsigned char IIP[]={ 40, 8, 48, 16, 56, 24, 64, 32,")
Inverse Initial Permutation unsigned char IIP[]={ 40, 8, 48, 16, 56, 24, 64, 32, 39, 7, 47, 15, 55, 23, 63, 31, 38, 6, 46, 14, 54, 22, 62, 30, 37, 5, 45, 13, 53, 21, 61, 29, 36, 4, 44, 12, 52, 20, 60, 28, 35, 3, 43, 11, 51, 19, 59, 27, 34, 2, 42, 10, 50, 18, 58, 26, 33, 1, 41, 9, 49, 17, 57, 25 }; Data[1] Data[0] Inverse Initial Permutation New. Data[1] New. Data[0]
Inverse Initial Permutation Inverse. Initial. Permutation(unsigned long *Data) { DWORD tmp. Mask; DWORD set. Mask; DWORD New. Data[2]={0, }; for(int i = 31 ; i >= 0 ; i--) { tmp. Mask = 0 x 00000001; set. Mask = 0 x 00000001<<(31 -i); if((IIP[i] <= 32) && (Data[1] & (tmp. Mask << (32 -IIP[i])))){ New. Data[1] = New. Data[1] | set. Mask; }else if((IIP[i] > 32) && (Data[0] & (tmp. Mask << (64 -IIP[i])))){ New. Data[1] = New. Data[1] | set. Mask; } }
Inverse Initial Permutation for(i = 63 ; i >=32 ; i--) { tmp. Mask = 0 x 00000001; set. Mask = 0 x 00000001<<(63 -i); if((IIP[i] <= 32) && (Data[1] & (tmp. Mask << (32 -IIP[i])))){ New. Data[0] = New. Data[0] | set. Mask; }else if((IIP[i] > 32) && (Data[0] & (tmp. Mask << (64 -IIP[i])))){ New. Data[0] = New. Data[0] | set. Mask; } } Data[1] = New. Data[1]; Data[0] = New. Data[0];
DES Round Structure • Uses two 32 -bit L & R halves • As for any Feistel cipher can describe as: Li = Ri– 1 Ri = Li– 1 xor F(Ri– 1, Ki) • Takes 32 -bit R half and 48 -bit subkey and: – – expands R to 48 -bits using expansion permutation adds to subkey passes through 8 S-boxes to get 32 -bit result finally permutes this using 32 -bit permutation function
Single Round of DES
E & P Table
![Expansion Permutation Expansion. Permutation(DWORD Right. Half, DWORD *e. Word) { DWORD New[2] = {0,](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-15.jpg "Expansion Permutation Expansion. Permutation(DWORD Right. Half, DWORD *e. Word) { DWORD New[2] = {0,")
Expansion Permutation Expansion. Permutation(DWORD Right. Half, DWORD *e. Word) { DWORD New[2] = {0, 0}; New[1] |= ((Right. Half & 0 x 00000001)<< 23); //32 th bit -> first bit of first word New[1] |=(((Right. Half & 0 x. F 8000000)>> 9) & 0 x 007 C 0000); // 1, 2, 3, 4, 5 bit -> 2, 3, 4, 5, 6 bit New[1] |= ((Right. Half & 0 x 1 F 800000)>> 11); New[1] |= ((Right. Half & 0 x 01 F 80000)>> 13); New[1] |= ((Right. Half & 0 x 001 F 8000)>> 15); New[0] |= ((Right. Half & 0 x 0001 F 800)<< 7); New[0] |= ((Right. Half & 0 x 00001 F 80)<< 5); New[0] |= ((Right. Half & 0 x 000001 F 8)<< 3); New[0] |= ((Right. Half & 0 x 0000001 F)<< 1); New[0] |= (((Right. Half & 0 x 80000000)>>31)&0 x 00000001); e. Word[1] = New[1]; e. Word[0] = New[0]; }
![Permutation Function unsigned char P[]={ 16, 7, 20, 21, 29, 12, 28, 17, 1,](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-16.jpg "Permutation Function unsigned char P[]={ 16, 7, 20, 21, 29, 12, 28, 17, 1,")
Permutation Function unsigned char P[]={ 16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10, 2, 8, 24, 14, 32, 27, 3, 9, 13, 30, 6, 22, 11, 4, 25 }; Permutation. Function(DWORD d. Word) { DWORD tmp. Mask = 0 x 00000001; DWORD key. Mask = 0 x 00000001; DWORD dw. Tmp = 0; for(int i = 0 ; i < 32 ; i++) { if(d. Word & (tmp. Mask << (32 -P[i]))) dw. Tmp |= (key. Mask<<(31 -i)); } return dw. Tmp; }
Calculation of F(R, K)
Substitution Boxes S • Have eight S-boxes which map 6 to 4 bits • Each S-box is actually 4 little 4 bit boxes – outer bits 1 & 6 (row bits) select one rows – inner bits 2 -5 (col bits) select one colum – result is 8 * 4 bits, i. e, 32 bits • Example: S(18 09 12 3 d 11 17 38 39) = 5 fd 25 e 03
Sample S-Boxes
Sample S-Boxes
![Substitution Choice unsigned char SBox_DES[8][4][16] = { {{14, 4, 13, 1, 2, 15, 11,](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-21.jpg "Substitution Choice unsigned char SBox_DES[8][4][16] = { {{14, 4, 13, 1, 2, 15, 11,")
Substitution Choice unsigned char SBox_DES[8][4][16] = { {{14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7}, {0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8}, {4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0}, {15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13}}, {{12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11}, {10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8}, {9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6}, {4, 3, 2, 12, 9, 5, 10, 11, 14, 1, 7, 6, 0, 8, 13}}, {{4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1}, {13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6}, {1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2}, {6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12}}, {{15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10}, {3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5}, {0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15}, {13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9}}, {{10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8}, {13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1}, {13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7}, {1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12}}, {{7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15}, {13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 1, 10, 14, 9}, {10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4}, {3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14}}, {{2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9}, {14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6}, {4, 2, 1, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14}, {11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3}}, {{13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7}, {1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2}, {7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8}, {2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11}} };
Substitution Choice unsigned long Substitution. Choice(DWORD *e. Word) { int row, col; DWORD tmp 0, tmp 1; tmp 0 = e. Word[0]; tmp 1 = e. Word[1]; int shift; e. Word[0] = 0; e. Word[1] = 0; for(int i = 0 ; i < 4 ; i++) { shift = (4*(3 -i)); tmp 1 <<= 6; row = ((tmp 1&0 x 20000000)>>28)|((tmp 1&0 x 01000000)>>24); col = (tmp 1&0 x 1 E 000000)>>25; e. Word[1] |= (SBox_DES[i ][row][col]<<shift); tmp 0 <<= 6; row = ((tmp 0&0 x 20000000)>>28)|((tmp 0&0 x 01000000)>>24); col = (tmp 0&0 x 1 E 000000)>>25; e. Word[0] |= (SBox_DES[i+4][row][col]<<shift); } e. Word[0] |= (e. Word[1]<<16); return e. Word[0]; }
DES Round(DWORD *d. Word, DWORD Round. Key 1, DWORD Round. Key 0) { DWORD tmp[2]={0, 0}; Expansion. Permutation(d. Word[0], tmp); tmp[1] = tmp[1] ^ Round. Key 1; tmp[0] = tmp[0] ^ Round. Key 0; tmp[0] = Substitution. Choice(tmp); tmp[0] = Permutation. Function(tmp[0]); tmp[0] = tmp[0] ^ d. Word[1]; d. Word[1] = d. Word[0]; d. Word[0] = tmp[0]; }
DES Key Schedule • Forms subkeys used in each round • Consists of: – initial permutation of the key (PC 1) which selects 56 -bits in two 28 -bit halves – 16 stages consisting of: • selecting 24 -bits from each half • permuting them by PC 2 for use in function f, • rotating each half separately either 1 or 2 places depending on the key rotation schedule K
DES Key Schedule Calculation 9, 18, 22, 25, 38, 43, 54
Permuted Choice 1 Permuted. Choice 1(DWORD *Key) { DWORD tmp. Mask; DWORD Key. Mask; DWORD New. Key[2]={0, 0}; tmp. Mask = 0 x 00000001; for(int i = 0 ; i < 28 ; i++) { Key. Mask = 0 x 08000000>>i; if((PC_1[i] <= 32) && (Key[1] & (tmp. Mask << (32 -PC_1[i])))){ New. Key[1] = New. Key[1] | Key. Mask; }else if((PC_1[i] > 32) && (Key[0] & (tmp. Mask << (64 -PC_1[i])))){ New. Key[1] = New. Key[1] | Key. Mask; } } unsigned char PC_1[]={ 57, 49, 41, 33, 25, 17, 9, 1, 58, 50, 42, 34, 26, 18, 10, 2, 59, 51, 43, 35, 27, 19, 11, 3, 60, 52, 44, 36, 63, 55, 47, 39, 31, 23, 15, 7, 62, 54, 46, 38, 30, 22, 14, 6, 61, 53, 45, 37, 29, 21, 13, 5, 28, 20, 12, 4 };
Permuted Choice 1 for( i = 28 ; i < 56 ; i++) { Key. Mask = 0 x 08000000>>(i-28); if((PC_1[i] <= 32) && (Key[1] & (tmp. Mask << (32 -PC_1[i])))){ New. Key[0] = New. Key[0] | Key. Mask; }else if((PC_1[i] > 32) && (Key[0] & (tmp. Mask << (64 -PC_1[i])))){ New. Key[0] = New. Key[0] | Key. Mask; } } Key[0] = New. Key[0]; Key[1] = New. Key[1]; }
Permuted Choice 2 Permuted. Choice 2(DWORD *Key) { DWORD tmp. Mask; DWORD Key. Mask; DWORD New. Key[2] = {0, 0}; unsigned char PC_2[]={ 14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10, 23, 19, 12, 4, 26, 8, 16, 7, 20, 13, 2, 41, 52, 31, 37, 47, 55, 30, 40, tmp. Mask = 0 x 00000001; 51, 45, 33, 48, 44, 49, 39, for(int i = 0 ; i < 24 ; i++) 56, { 34, 53, 46, 42, 50, 36, 29, Key. Mask = 0 x 00800000>>i; 32, if((PC_2[i] <= 28) && (Key[1] & (tmp. Mask << (28 -PC_2[i])))){}; New. Key[1] = New. Key[1] | Key. Mask; }else if((PC_2[i] > 28) && (Key[0] & (tmp. Mask << (56 -PC_2[i])))){ New. Key[1] = New. Key[1] | Key. Mask; } }
Permuted Choice 2 for( i = 24 ; i < 48 ; i++) { Key. Mask = 0 x 00800000>>(i-24); if((PC_2[i] <= 28) && (Key[1] & (tmp. Mask << (28 -PC_2[i])))){ New. Key[0] = New. Key[0] | Key. Mask; }else if((PC_2[i] > 28) && (Key[0] & (tmp. Mask << (56 -PC_2[i])))){ New. Key[0] = New. Key[0] | Key. Mask; } } Key[0] = New. Key[0]; Key[1] = New. Key[1]; }
![Key Schedule Key. Schedule(char *Key, DWORD *Round. Key) { int SHIFT=0; DWORD dw. Key[2]={0,](http://slidetodoc.com/presentation_image/2f9ff079e98efa45cf5a89409a4db0db/image-30.jpg "Key Schedule Key. Schedule(char *Key, DWORD *Round. Key) { int SHIFT=0; DWORD dw. Key[2]={0,")
Key Schedule Key. Schedule(char *Key, DWORD *Round. Key) { int SHIFT=0; DWORD dw. Key[2]={0, 0}; DWORD tmp 0, tmp 1; for(int i = 0 ; i < 4 ; i++) { SHIFT =((3 -i)*8); dw. Key[1] ^= ((DWORD)Key[i ])<<SHIFT; dw. Key[0] ^= ((DWORD)Key[i+4 ])<<SHIFT; } Permuted. Choice 1(dw. Key);
Key Schedule for(i = 0 ; i < 16 ; i++) { //Left Shift if(LSHIFT[i] == 1) { tmp 0 = ((dw. Key[0] & 0 x 08000000) >> 27); tmp 0 |= ((dw. Key[0] & 0 x 07 FFFFFF) << 1); dw. Key[0] = tmp 0; tmp 1 = ((dw. Key[1] & 0 x 08000000) >> 27); tmp 1 |= ((dw. Key[1] & 0 x 07 FFFFFF) << 1); dw. Key[1] = tmp 1; }else //2 bit-shift { tmp 0 = ((dw. Key[0] & 0 x 0 c 000000) >> 26); tmp 0 |= ((dw. Key[0] & 0 x 03 FFFFFF) << 2); dw. Key[0] = tmp 0; tmp 1 = ((dw. Key[1] & 0 x 0 c 000000) >> 26); tmp 1 |= ((dw. Key[1] & 0 x 03 FFFFFF) << 2); dw. Key[1] = tmp 1; } Permuted. Choice 2(dw. Key); Round. Key[2*i+1] = dw. Key[1]; Round. Key[2*i] = dw. Key[0]; dw. Key[1] = tmp 1; dw. Key[0] = tmp 0; } } const unsigned char LSHIFT[]={ 1, 1, 2, 2, 2, 1 };
Strength of DES – Key Size • 56 -bit keys have 256 = 7. 2 x 1016 values • Brute force search looks hard • Recent advances have shown that it is possible – in 1997 on Internet in a few months – in 1998 on dedicated h/w (EFF) in a few days – in 1999 above combined in 22 hrs! • still must be able to recognize plaintext • now considering alternatives to DES
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