vulcan-cryptanalysis

C
Vulcan Decrypt Simulation
%-----------------------------------------------------------
% Vulcan decryption simulation
% 2014-06-04 --- CJR
% inputs: 128-bit SRAM array contents "sram"
% 8-bit CV shift register contents "cv8"
% n-bit ciphertext "cti"
% outputs: n-bit plaintext "pto"
% > first 31 bits of plaintext will be gibberish
% decrypts ciphertext into plaintext using Vulcan cipher
% requires "key schedule" to have been run prior to use
%-----------------------------------------------------------
% check user-supplied inputs for simple errors
if((exist(’sram’) == 0)||(length(sram) != 128))
error("128-bit SRAM array not found -- run key schedule")
end
if((exist(’cv8’) == 0)||(length(cv8) != 8))
error("8-bit CV shift register not found -- run key schedule")
end
if(exist(’cti’) == 0)
error("ciphertext input not found -- create some ciphertext")
end
% set up required variables
last = 0; % last ciphertext input bit for differential decoder
ctsr = zeros(1,31); % 31-bit ciphertext shift-register
pto = zeros(1,length(cti)); % pre-allocate plaintext output
% process all bits of ciphertext input
for ii = 1:length(cti)
% differentially decode the ciphertext input bit
ct0 = bitxor(cti(ii),last);
last = cti(ii);
% compute the current SRAM address
addr = ctsr(1:7);
addr = addr*[1 2 4 8 16 32 64]’;
addr = addr+1;
% combine SRAM bit with CT21
keyb = sram(addr);
m0 = bitxor(ctsr(21),keyb);
% compute the XOR tree results
pt = ct0;
pt = bitxor(pt,bitand(cv8(1),ctsr(22)));
pt = bitxor(pt,bitand(cv8(2),ctsr(23)));
pt = bitxor(pt,bitand(cv8(3),ctsr(24)));
pt = bitxor(pt,bitand(cv8(4),ctsr(25)));
pt = bitxor(pt,bitand(cv8(5),ctsr(26)));
pt = bitxor(pt,bitand(cv8(6),ctsr(27)));
pt = bitxor(pt,bitand(cv8(7),ctsr(28)));
pt = bitxor(pt,bitand(cv8(8),ctsr(29)));
pt = bitxor(pt,ctsr(30));
% save decrypted plaintext
pto(ii) = pt;
% clock the ciphertext shift-register
ctsr = [ct0 ctsr(1:20) m0 ctsr(22:30)];
end
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