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This code works on encryption, what are the mistakes that make it not work?

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khalil Z. Abu-Haltam
khalil Z. Abu-Haltam on 2 Oct 2015
Closed: Walter Roberson on 2 Nov 2015
function [varargout] = DES(input64,mode,key)
%DES: Data Encryption Standard
% Encrypt/Decrypt a 64-bit message using a 64-bit key using the Feistel Network
% -------------------------------------------------------------------------
% Inputs:
% input64 = a 64-bit message
% mode = either 'ENC' encryption or 'DEC' decryption (default 'ENC')
% key = a 56/64-bit key (optional under 'ENC', but mandatory under 'DEC')
% Outputs:
% varargout{1} = output64, a 64-bit message after encryption/decryption
% varargout{2} = a 64-bit key, if a 64-bit key is not provided as an input
% -------------------------------------------------------------------------
% Demos:
% plaintext = round(rand(1,64));
% [ciphertext,key] = DES(plaintext); % Encryption syntex 1
% [ciphertext1,key] = DES(plaintext,'ENC'); % Encryption syntex 2
% deciphertext1 = DES(ciphertext1,'DEC',key);% Decryption syntex
%
% key56 = round(rand(1,56));
% [ciphertext2,key64] = DES(plaintext,'ENC',key56);% Encryption syntex 3 (56-bit key)
% deciphertext2 = DES(ciphertext2,'DEC',key64); % Decryption syntex (64-bit key)
% ciphertext3 = DES(plaintext,'ENC',key64); % Encryption syntex 3 (64-bit key)
% deciphertext3 = DES(ciphertext3,'DEC',key56); % Decryption syntex (56-bit key)
%
% % plot results
% subplot(4,2,1),plot(plaintext),ylim([-.5,1.5]),xlim([1,64]),title('plaintext')
% subplot(4,2,2),plot(ciphertext),ylim([-.5,1.5]),xlim([1,64]),title('ciphertext')
% subplot(4,2,3),plot(deciphertext1),ylim([-.5,1.5]),xlim([1,64]),title('deciphertext1')
% subplot(4,2,4),plot(ciphertext1),ylim([-.5,1.5]),xlim([1,64]),title('ciphertext1')
% subplot(4,2,5),plot(deciphertext2),ylim([-.5,1.5]),xlim([1,64]),title('deciphertext2')
% subplot(4,2,6),plot(ciphertext2),ylim([-.5,1.5]),xlim([1,64]),title('ciphertext2')
% subplot(4,2,7),plot(deciphertext3),ylim([-.5,1.5]),xlim([1,64]),title('deciphertext3')
% subplot(4,2,8),plot(ciphertext3),ylim([-.5,1.5]),xlim([1,64]),title('ciphertext3')
% -------------------------------------------------------------------------
% NOTE:
% 1. If a 64-bit key is provided, then its bit parities will be checked. If
% a 56-bit key is provided, then it is automatically added 8 partity
% checking bits. However, the 8 parity bits are never used in
% DES encryption/decryption process. They are included just for the
% completeness of a DES implementation.
% 2. Cipher modes are not provided in this simple script. If you are
% interested or do not know what does cipher modes mean, please go to page
% http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation
% for details. Please keep in mind that selecting an inappropriate working
% mode may extremely weaken the security of your messages.
% 3. A general description of DES can be found at its wiki page:
% http://en.wikipedia.org/wiki/Data_Encryption_Standard
% The detailed cryptographical primitives can be found under the page:
% http://en.wikipedia.org/wiki/DES_supplementary_material
% If you want to speed-up the DES code here, you can simply store these
% primitives in memory and call them when you need.
% -------------------------------------------------------------------------
% By Yue (Rex) Wu
% ECE Dept @ Tufts Univ.
% 08/18/2012
% If you find bugs, please email me via ywu03@ece.tufts.edu
% -------------------------------------------------------------------------
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0. Initialization %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 0.1 check input
error (nargchk(1,3,nargin));
switch nargin
case 1
mode = 'ENC';
K = round(rand(8,7));
K(:,8) = mod(sum(K,2),2); % note these eight bits of key are never used in encryption
K = reshape(K',1,64);
varargout{2} = K;
case 2
switch mode
case 'ENC'
K = round(rand(8,7));
K(:,8) = mod(sum(K,2),2); % note these eight bits of key are never used in encryption
K = reshape(K',1,64);
varargout{2} = K;
case 'DEC'
error('Key has to be provided in decryption mode (DEC)')
otherwise
error('WRONG working mode!!! Select either encrtyption mode: ENC or decryption mode: DEC !!!')
end
case 3
if isempty(setdiff(unique(key),[0,1])) % check provided key type
if numel(key) == 64 % check provided key parity
keyParityCheck = @(k) (sum(mod(sum(reshape(k,8,8)),2))==0);
if keyParityCheck(key) == 1
K = key(:)';
else
error('Key parity check FAILED!!!')
end
elseif numel(key) == 56 % add parity bits
K = reshape(key,7,8)';
K(:,8) = mod(sum(K,2),2); % note these eight bits of key are never used in encryption
K = reshape(K',1,64);
varargout{2} = K;
display('Key parity bits added')
else
error('Key has to be either 56 or 64-bit long!!!')
end
else
error('Key has to be binary!!!')
end
end
% 0.2 check message length and type
if numel(input64) == 64 && isempty(setdiff(unique(input64),[0,1]))
P = input64;
else
error('Message has to be a 64-bit message!!!')
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1. Cryptographical primitives %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 1.1 define splitting function
HALF_L = @(message) message(1:32);
HALF_R = @(message) message(33:64);
% 1.2 define expansion function
EF = @(halfMessage) [halfMessage([32,4:4:28])',(reshape(halfMessage,4,8))',halfMessage([5:4:29,1])'];
% 1.3 define key mixing (KM)
KM = @(expandedHalfMessage,rK) xor(expandedHalfMessage,reshape(rK,6,8)');
% 1.4 define eight substitution tables
% input: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
st{1} = [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];
st{2} = [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];
st{3} = [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];
st{4} = [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];
st{5} = [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];
st{6} = [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];
st{7} = [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];
st{8} = [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];
% the eight binary s-boxes
for i = 1:8
ST{i} = mat2cell(blkproc(st{i},[1,1],@(x) de2bi(x,4,'left-msb')),ones(1,4),ones(1,16)*4);
end
% 1.5 define subsitution function (SBOX)
SUBS = @(expandedHalfMessage,blkNo) ST{blkNo}{bi2de(expandedHalfMessage(blkNo,[1,6]),'left-msb')+1,bi2de(expandedHalfMessage(blkNo,[2:5]),'left-msb')+1};
SBOX = @(expandedHalfMessage) [SUBS(expandedHalfMessage,1);SUBS(expandedHalfMessage,2);...
SUBS(expandedHalfMessage,3);SUBS(expandedHalfMessage,4);...
SUBS(expandedHalfMessage,5);SUBS(expandedHalfMessage,6);...
SUBS(expandedHalfMessage,7);SUBS(expandedHalfMessage,8)];
% 1.6 define permutation function (PBOX)
PBOX = @(halfMessage) halfMessage([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]);
% 1.7 define initial permutation (IP)
IP = @(message) message([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]);
% 1.8 define final permutation (FP)
FP = @(message) message([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]);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
2. key schedule %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 2.1 define permuted choice 1 (PC1)
PC1L = @(key64) key64([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]);
PC1R = @(key64) key64([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]);
% 2.2 define permuted choice 2 (PC2)
PC2 = @(key56) key56([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]);
% 2.3 define rotations in key-schedule (RK)
% round# 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
RK = [1 1 2 2 2 2 2 2 1 2 2 2 2 2 2 1];
% 2.4 define key shift function (KS)
KS = @(key28,s) [key28(s+1:end),key28(1:s)];
% 2.5 define sub-keys for each round
leftHKey = PC1L(K); % 28-bit half key
rightHKey = PC1R(K);% 28-bit half key
for i = 1:16
leftHKey = KS(leftHKey,RK(i));
rightHKey = KS(rightHKey,RK(i));
key56 = [leftHKey ,rightHKey];
subKeys(i,:) = PC2(key56(:));
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
3. DES main loop %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 3.1 initial permutation
C = IP(P);
switch mode
case 'ENC' % if encryption, split 64 message to two halves
L{1} = HALF_L(C); % left-half 32-bit
R{1} = HALF_R(C); % right-half 32-bit
case 'DEC' % if decryption, swapping two halves
L{1} = HALF_R(C);
R{1} = HALF_L(C);
end
% 3.2 cipher round 1 to 16
for i = 1:16
L{i+1} = R{i}; % half key: 32-bit
expended_R = EF(R{i}); % expended half key: 32-bit to 48-bit
switch mode
case 'ENC' % if encryption, apply sub-keys in the original order
mixed_R = KM(expended_R,subKeys(i,:)); % mixed with sub-key: 48-bit
case 'DEC' % if decryption, apply sub-keys in the reverse order
mixed_R = KM(expended_R,subKeys(16-i+1,:)); % mixed with sub-key: 48-bit
end
substituted_R = SBOX(mixed_R); % substitution: 48-bit to 32-bit
permuted_R = PBOX(reshape(substituted_R',1,32)); % permutation: 32-bit
R{i+1} = xor(L{i},permuted_R); % Feistel function: 32-bit
end
% 3.3 final permutation
switch mode
case 'ENC'
C = [L{end},R{end}];
case 'DEC'
C = [R{end},L{end}];
end
output64 = FP(C);
varargout{1} = output64;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
END %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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Answers (1)

Nicholas Felix
Nicholas Felix on 1 Nov 2015
Not sure about that code. I used much of Yue Wu's code as an example, along with the NIST DES standard publication to create a working code.
DES 64

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