How many bits is a DES round key?
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Data encryption standard (DES) has been found vulnerable to very powerful attacks and therefore, the popularity of DES has been found slightly on the decline. DES is a block cipher and encrypts data in blocks of size of 64 bits each, which means 64 bits of plain text go as the input to DES, which produces 64 bits of ciphertext. The same algorithm and key are used for encryption and decryption, with minor differences. The key length is 56 bits. The basic idea is shown in the figure. Show  We have mentioned that DES uses a 56-bit key. Actually, the initial key consists of 64 bits. However, before the DES process even starts, every 8th bit of the key is discarded to produce a 56-bit key. That is bit positions 8, 16, 24, 32, 40, 48, 56, and 64 are discarded. Thus, the discarding of every 8th bit of the key produces a 56-bit
key from the original 64-bit key.
Initial Permutation (IP): As we have noted, the initial permutation (IP) happens only once and it happens before the first round. It suggests how the transposition in IP should proceed, as shown in the figure. For example, it says that the IP replaces the first bit of the original plain text block with the 58th bit of the original plain text, the second bit with the 50th bit of the original plain text block, and so on. This is nothing but jugglery of bit positions of the original plain text block. the same rule applies to all the other bit positions shown in the figure. As we have noted after IP is done, the resulting 64-bit permuted text block is divided into two half blocks. Each half-block consists of 32 bits, and each of the 16 rounds, in turn, consists of the broad level steps outlined in the figure. Step-1: Key transformation: We have noted initial 64-bit key is transformed into a 56-bit key by discarding every 8th bit of the initial key. Thus, for each a 56-bit key is available. From this 56-bit key, a different 48-bit Sub Key is generated during each round using a process called key transformation. For this, the 56-bit key is divided into two halves, each of 28 bits. These halves are circularly shifted left by one or two positions, depending on the round. For example, if the round numbers 1, 2, 9, or 16 the shift is done by only one position for other rounds, the circular shift is done by two positions. The number of key bits shifted per round is shown in the figure. After an appropriate shift, 48 of the 56 bits are selected. for selecting 48 of the 56 bits the table is shown in the figure given below. For instance, after the shift, bit number 14 moves to the first position, bit number 17 moves to the second position, and so on. If we observe the table carefully, we will realize that it contains only 48-bit positions. Bit number 18 is discarded (we will not find it in the table), like 7 others, to reduce a 56-bit key to a 48-bit key. Since the key transformation process involves permutation as well as a selection of a 48-bit subset of the original 56-bit key it is called Compression Permutation. Because of this compression permutation technique, a different subset of key bits is used in each round. That makes DES not easy to crack. Step-2: Expansion Permutation: Recall that after the initial permutation, we had two 32-bit plain text areas called Left Plain Text(LPT) and Right Plain Text(RPT). During the expansion permutation, the RPT is expanded from 32 bits to 48 bits. Bits are permuted as well hence called expansion permutation. This happens as the 32-bit RPT is divided into 8 blocks, with each block consisting of 4 bits. Then, each 4-bit block of the previous step is then expanded to a corresponding 6-bit block, i.e., per 4-bit block, 2 more bits are added. This process results in expansion as well as a permutation of the input bit while creating output. The key transformation process compresses the 56-bit key to 48 bits. Then the expansion permutation process expands the 32-bit RPT to 48-bits. Now the 48-bit key is XOR with 48-bit RPT and the resulting output is given to the next step, which is the S-Box substitution. C++#include using namespace std; string hex2bin(string s) { unordered_map mp['0'] = "0000"; mp['1'] = "0001"; mp['2'] = "0010"; mp['3'] = "0011"; mp['4'] = "0100"; mp['5'] = "0101"; mp['6'] = "0110"; mp['7'] = "0111"; mp['8'] = "1000"; mp['9'] = "1001"; mp['A'] = "1010"; mp['B'] = "1011"; mp['C'] = "1100"; mp['D'] = "1101"; mp['E'] = "1110"; mp['F'] = "1111"; string bin = ""; for (int i = 0; i < s.size(); i++) { bin += mp[s[i]]; } return bin; } string bin2hex(string s) { unordered_map mp["0000"] = "0"; mp["0001"] = "1"; mp["0010"] = "2"; mp["0011"] = "3"; mp["0100"] = "4"; mp["0101"] = "5"; mp["0110"] = "6"; mp["0111"] = "7"; mp["1000"] = "8"; mp["1001"] = "9"; mp["1010"] = "A"; mp["1011"] = "B"; mp["1100"] = "C"; mp["1101"] = "D"; mp["1110"] = "E"; mp["1111"] = "F"; string hex = ""; for (int i = 0; i < s.length(); i += 4) { string ch = ""; ch += s[i]; ch += s[i + 1]; ch += s[i + 2]; ch += s[i + 3]; hex += mp[ch]; } return hex; } string permute(string k, int* arr, int n) { string per = ""; for (int i = 0; i < n; i++) { per += k[arr[i] - 1]; } return per; } string shift_left(string k, int shifts) { string s = ""; for (int i = 0; i < shifts; i++) { for (int j = 1; j < 28; j++) { s += k[j]; } s += k[0]; k = s; s = ""; } return k; } string xor_(string a, string b) { string ans = ""; for (int i = 0; i < a.size(); i++) { if (a[i] == b[i]) { ans += "0"; } else { ans += "1"; } } return ans; } string encrypt(string pt, vector { pt = hex2bin(pt); int initial_perm[64] = { 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 }; pt = permute(pt, initial_perm, 64); cout << "After initial permutation: " << bin2hex(pt) << endl; string left = pt.substr(0, 32); string right = pt.substr(32, 32); cout << "After splitting: L0=" << bin2hex(left) << " R0=" << bin2hex(right) << endl; int exp_d[48] = { 32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17, 16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25, 24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1 }; int s[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 }, { 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, 12, 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, 11, 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 }, { 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, 15, 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 }, { 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 } }; int per[32] = { 16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10, 2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25 }; cout << endl; for (int i = 0; i < 16; i++) { string right_expanded = permute(right, exp_d, 48); string x = xor_(rkb[i], right_expanded); string op = ""; for (int i = 0; i < 8; i++) { int row = 2 * int(x[i * 6] - '0') + int(x[i * 6 + 5] - '0'); int col = 8 * int(x[i * 6 + 1] - '0') + 4 * int(x[i * 6 + 2] - '0') + 2 * int(x[i * 6 + 3] - '0') + int(x[i * 6 + 4] - '0'); int val = s[i][row][col]; op += char(val / 8 + '0'); val = val % 8; op += char(val / 4 + '0'); val = val % 4; op += char(val / 2 + '0'); val = val % 2; op += char(val + '0'); } op = permute(op, per, 32); x = xor_(op, left); left = x; if (i != 15) { swap(left, right); } cout << "Round " << i + 1 << " " << bin2hex(left) << " " << bin2hex(right) << " " << rk[i] << endl; } string combine = left + right; int final_perm[64] = { 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 }; string cipher = bin2hex(permute(combine, final_perm, 64)); return cipher; } int main() { string pt, key; pt = "123456ABCD132536"; key = "AABB09182736CCDD"; key = hex2bin(key); int keyp[56] = { 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 }; key = permute(key, keyp, 56); int shift_table[16] = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 }; int key_comp[48] = { 14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10, 23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2, 41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48, 44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32 }; string left = key.substr(0, 28); string right = key.substr(28, 28); vector vector for (int i = 0; i < 16; i++) { left = shift_left(left, shift_table[i]); right = shift_left(right, shift_table[i]); string combine = left + right; string RoundKey = permute(combine, key_comp, 48); rkb.push_back(RoundKey); rk.push_back(bin2hex(RoundKey)); } cout << "\nEncryption:\n\n"; string cipher = encrypt(pt, rkb, rk); cout << "\nCipher Text: " << cipher << endl; cout << "\nDecryption\n\n"; reverse(rkb.begin(), rkb.end()); reverse(rk.begin(), rk.end()); string text = encrypt(cipher, rkb, rk); cout << "\nPlain Text: " << text << endl; } Javaimport java.util.*; class Main { private static class DES { int[] 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 }; int[] IP1 = { 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 }; int[] PC1 = { 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 }; int[] PC2 = { 14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10, 23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2, 41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48, 44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32 }; int[] EP = { 32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17, 16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25, 24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1 }; int[] 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, 19, 13, 30, 6, 22, 11, 4, 25 }; int[][][] sbox = { { { 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 } }, { { 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, 12, 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, 11, 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 } }, { { 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, 15, 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 } }, { { 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 } } }; int[] shiftBits = { 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 }; String hextoBin(String input) { int n = input.length() * 4; input = Long.toBinaryString( Long.parseUnsignedLong(input, 16)); while (input.length() < n) input = "0" + input; return input; } String binToHex(String input) { int n = (int)input.length() / 4; input = Long.toHexString( Long.parseUnsignedLong(input, 2)); while (input.length() < n) input = "0" + input; return input; } String permutation(int[] sequence, String input) { String output = ""; input = hextoBin(input); for (int i = 0; i < sequence.length; i++) output += input.charAt(sequence[i] - 1); output = binToHex(output); return output; } String xor(String a, String b) { long t_a = Long.parseUnsignedLong(a, 16); long t_b = Long.parseUnsignedLong(b, 16); t_a = t_a ^ t_b; a = Long.toHexString(t_a); while (a.length() < b.length()) a = "0" + a; return a; } String leftCircularShift(String input, int numBits) { int n = input.length() * 4; int perm[] = new int[n]; for (int i = 0; i < n - 1; i++) perm[i] = (i + 2); perm[n - 1] = 1; while (numBits-- > 0) input = permutation(perm, input); return input; } String[] getKeys(String key) { String keys[] = new String[16]; key = permutation(PC1, key); for (int i = 0; i < 16; i++) { key = leftCircularShift( key.substring(0, 7), shiftBits[i]) + leftCircularShift(key.substring(7, 14), shiftBits[i]); keys[i] = permutation(PC2, key); } return keys; } String sBox(String input) { String output = ""; input = hextoBin(input); for (int i = 0; i < 48; i += 6) { String temp = input.substring(i, i + 6); int num = i / 6; int row = Integer.parseInt( temp.charAt(0) + "" + temp.charAt(5), 2); int col = Integer.parseInt( temp.substring(1, 5), 2); output += Integer.toHexString( sbox[num][row][col]); } return output; } String round(String input, String key, int num) { String left = input.substring(0, 8); String temp = input.substring(8, 16); String right = temp; temp = permutation(EP, temp); temp = xor(temp, key); temp = sBox(temp); temp = permutation(P, temp); left = xor(left, temp); System.out.println("Round " + (num + 1) + " " + right.toUpperCase() + " " + left.toUpperCase() + " " + key.toUpperCase()); return right + left; } String encrypt(String plainText, String key) { int i; String keys[] = getKeys(key); plainText = permutation(IP, plainText); System.out.println( "After initial permutation: " + plainText.toUpperCase()); System.out.println( "After splitting: L0=" + plainText.substring(0, 8).toUpperCase() + " R0=" + plainText.substring(8, 16).toUpperCase() + "\n"); for (i = 0; i < 16; i++) { plainText = round(plainText, keys[i], i); } plainText = plainText.substring(8, 16) + plainText.substring(0, 8); plainText = permutation(IP1, plainText); return plainText; } String decrypt(String plainText, String key) { int i; String keys[] = getKeys(key); plainText = permutation(IP, plainText); System.out.println( "After initial permutation: " + plainText.toUpperCase()); System.out.println( "After splitting: L0=" + plainText.substring(0, 8).toUpperCase() + " R0=" + plainText.substring(8, 16).toUpperCase() + "\n"); for (i = 15; i > -1; i--) { plainText = round(plainText, keys[i], 15 - i); } plainText = plainText.substring(8, 16) + plainText.substring(0, 8); plainText = permutation(IP1, plainText); return plainText; } } public static void main(String args[]) { String text = "123456ABCD132536"; String key = "AABB09182736CCDD"; DES cipher = new DES(); System.out.println("Encryption:\n"); text = cipher.encrypt(text, key); System.out.println( "\nCipher Text: " + text.toUpperCase() + "\n"); System.out.println("Decryption\n"); text = cipher.decrypt(text, key); System.out.println( "\nPlain Text: " + text.toUpperCase()); } } Pythondef hex2bin(s): mp = {'0' : "0000", '1' : "0001", '2' : "0010", '3' : "0011", '4' : "0100", '5' : "0101", '6' : "0110", '7' : "0111", '8' : "1000", '9' : "1001", 'A' : "1010", 'B' : "1011", 'C' : "1100", 'D' : "1101", 'E' : "1110", 'F' : "1111" } bin = "" for i in range(len(s)): bin = bin + mp[s[i]] return bin def bin2hex(s): mp = {"0000" : '0', "0001" : '1', "0010" : '2', "0011" : '3', "0100" : '4', "0101" : '5', "0110" : '6', "0111" : '7', "1000" : '8', "1001" : '9', "1010" : 'A', "1011" : 'B', "1100" : 'C', "1101" : 'D', "1110" : 'E', "1111" : 'F' } hex = "" for i in range(0,len(s),4): ch = "" ch = ch + s[i] ch = ch + s[i + 1] ch = ch + s[i + 2] ch = ch + s[i + 3] hex = hex + mp[ch] return hex def bin2dec(binary): binary1 = binary decimal, i, n = 0, 0, 0 while(binary != 0): dec = binary % 10 decimal = decimal + dec * pow(2, i) binary = binary//10 i += 1 return decimal def dec2bin(num): res = bin(num).replace("0b", "") if(len(res)%4 != 0): div = len(res) / 4 div = int(div) counter =(4 * (div + 1)) - len(res) for i in range(0, counter): res = '0' + res return res def permute(k, arr, n): permutation = "" for i in range(0, n): permutation = permutation + k[arr[i] - 1] return permutation def shift_left(k, nth_shifts): s = "" for i in range(nth_shifts): for j in range(1,len(k)): s = s + k[j] s = s + k[0] k = s s = "" return k def xor(a, b): ans = "" for i in range(len(a)): if a[i] == b[i]: ans = ans + "0" else: ans = ans + "1" return ans initial_perm = [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] exp_d = [32, 1 , 2 , 3 , 4 , 5 , 4 , 5, 6 , 7 , 8 , 9 , 8 , 9 , 10, 11, 12, 13, 12, 13, 14, 15, 16, 17, 16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25, 24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1 ] per = [ 16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10, 2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25 ] sbox = [[[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 ]], [[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, 12, 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, 11, 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 ]], [ [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, 15, 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] ], [ [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] ] ] final_perm = [ 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 ] def encrypt(pt, rkb, rk): pt = hex2bin(pt) pt = permute(pt, initial_perm, 64) print("After initial permutation", bin2hex(pt)) left = pt[0:32] right = pt[32:64] for i in range(0, 16): right_expanded = permute(right, exp_d, 48) xor_x = xor(right_expanded, rkb[i]) sbox_str = "" for j in range(0, 8): row = bin2dec(int(xor_x[j * 6] + xor_x[j * 6 + 5])) col = bin2dec(int(xor_x[j * 6 + 1] + xor_x[j * 6 + 2] + xor_x[j * 6 + 3] + xor_x[j * 6 + 4])) val = sbox[j][row][col] sbox_str = sbox_str + dec2bin(val) sbox_str = permute(sbox_str, per, 32) result = xor(left, sbox_str) left = result if(i != 15): left, right = right, left print("Round ", i + 1, " ", bin2hex(left), " ", bin2hex(right), " ", rk[i]) combine = left + right cipher_text = permute(combine, final_perm, 64) return cipher_text pt = "123456ABCD132536" key = "AABB09182736CCDD" key = hex2bin(key) keyp = [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 ] key = permute(key, keyp, 56) shift_table = [1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 ] key_comp = [14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10, 23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2, 41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48, 44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32 ] left = key[0:28] right = key[28:56] rkb = [] rk = [] for i in range(0, 16): left = shift_left(left, shift_table[i]) right = shift_left(right, shift_table[i]) combine_str = left + right round_key = permute(combine_str, key_comp, 48) rkb.append(round_key) rk.append(bin2hex(round_key)) print("Encryption") cipher_text = bin2hex(encrypt(pt, rkb, rk)) print("Cipher Text : ",cipher_text) print("Decryption") rkb_rev = rkb[::-1] rk_rev = rk[::-1] text = bin2hex(encrypt(cipher_text, rkb_rev, rk_rev)) print("Plain Text : ",text) Output: Encryption: After initial permutation: 14A7D67818CA18AD After splitting: L0=14A7D678 R0=18CA18AD Round 1 18CA18AD 5A78E394 194CD072DE8C Round 2 5A78E394 4A1210F6 4568581ABCCE Round 3 4A1210F6 B8089591 06EDA4ACF5B5 Round 4 B8089591 236779C2 DA2D032B6EE3 Round 5 236779C2 A15A4B87 69A629FEC913 Round 6 A15A4B87 2E8F9C65 C1948E87475E Round 7 2E8F9C65 A9FC20A3 708AD2DDB3C0 Round 8 A9FC20A3 308BEE97 34F822F0C66D Round 9 308BEE97 10AF9D37 84BB4473DCCC Round 10 10AF9D37 6CA6CB20 02765708B5BF Round 11 6CA6CB20 FF3C485F 6D5560AF7CA5 Round 12 FF3C485F 22A5963B C2C1E96A4BF3 Round 13 22A5963B 387CCDAA 99C31397C91F Round 14 387CCDAA BD2DD2AB 251B8BC717D0 Round 15 BD2DD2AB CF26B472 3330C5D9A36D Round 16 19BA9212 CF26B472 181C5D75C66D Cipher Text: C0B7A8D05F3A829C Decryption After initial permutation: 19BA9212CF26B472 After splitting: L0=19BA9212 R0=CF26B472 Round 1 CF26B472 BD2DD2AB 181C5D75C66D Round 2 BD2DD2AB 387CCDAA 3330C5D9A36D Round 3 387CCDAA 22A5963B 251B8BC717D0 Round 4 22A5963B FF3C485F 99C31397C91F Round 5 FF3C485F 6CA6CB20 C2C1E96A4BF3 Round 6 6CA6CB20 10AF9D37 6D5560AF7CA5 Round 7 10AF9D37 308BEE97 02765708B5BF Round 8 308BEE97 A9FC20A3 84BB4473DCCC Round 9 A9FC20A3 2E8F9C65 34F822F0C66D Round 10 2E8F9C65 A15A4B87 708AD2DDB3C0 Round 11 A15A4B87 236779C2 C1948E87475E Round 12 236779C2 B8089591 69A629FEC913 Round 13 B8089591 4A1210F6 DA2D032B6EE3 Round 14 4A1210F6 5A78E394 06EDA4ACF5B5 Round 15 5A78E394 18CA18AD 4568581ABCCE Round 16 14A7D678 18CA18AD 194CD072DE8C Plain Text: 123456ABCD132536
What is the round key size in DES?1. The block size in DES is 64 bits. The cipher key size is 56 bits. The round key size is 48 bits. Which algorithm uses 56The DES algorithm uses a key of 56-bit size. Using this key, the DES takes a block of 64-bit plain text as input and generates a block of 64-bit cipher text. The DES process has several steps involved in it, where each step is called a round. How many round keys are generated in the DES algorithm?Data Encryption Standard. How many bits is a DES key?Data Encryption Standard. Why does DES have a 48In round 1, 2, 9, and 16 shifting is one bit and in the other rounds it is two bits. The two parts are integrate to build a 56 bit part. Thus the compression D-box transform it into 48 bit. These 48 bits are being utilized as a key for a round.
Why does DES use a 56DES works by encrypting groups of 64 message bits, which is the same as 16 hexadecimal numbers. To do the encryption, DES uses "keys" where are also apparently 16 hexadecimal numbers long, or apparently 64 bits long. However, every 8th key bit is ignored in the DES algorithm, so that the effective key size is 56 bits.
How many bytes is a DES?DES has a 56-bit key in 8-bytes. The length of the output depends on the length of the input, mode and padding, not the key. Note: The LSb (least significant bit) of each key byte is reserved for parity, depending on the DES implementation parity may or not be checked.
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