I have done encryption of audio file using AES algorithm....the code works but it only takes first the 16 values of an audio file mean at every iteration. It will take 16 values, that means at the end I get a large number of cipher texts. For example, audio file size (8172) so , (8172/16) = 510. In the end, I get almost 510 ciphertexts. I'm confused about how to embed these ciphertexts. I have no idea what to do...it is not reading the whole file. Please help me sort out the issue...these are the changes which I have done in the demo file of AES algo.
[plaintext1,fs]= wavread('A1.wav','native');
plaintext1 = plaintext(1:16);
plaintext_hex = dec2hex( plaintext1);
plaintext = hex2dec (plaintext_hex);
p1 = [];
for i = 1;
plain = size(plaintext1/16);
i = i+1;
end
Hi! I'm not sure I understand very well what your problem is, but I think having a look to chaining modes (aka mode of operation) would help.
AES (in its 128 bits version) actually works by processing blocks of 16 bytes. Therefore, if your (not necessarily audio) file is 8172 bytes long, as 8172 = 510*16+12, you will get 511 ciphertexts corresponding to your 510 first block encrypted as they are, followed by the last 12 bytes padded with 4 bytes (to obtain a block of 16 bytes) encrypted.
For security purposes, you may want to add a mode of operation to chain your different ciphertexts: http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
Hope it'll help. Bests
because in ( plaintext1 = plaintext(1:16); ) you are just reading the first 16 elements and ignoring the rest of it!!! Make a loop as follows:
for i = 1:8172/16
plaintext1 = plaintext(16*(i-1)+1 :16*(i-1) + 16);
...
end
i have applied your mentioned lines
for i = 1:8172/16
plaintext1 = plaintext(16*(i-1)+1 :16*(i-1) + 16);
but after applying this i got the error mentioned below:
ERROR : Index exceeds matrix dimensions.
Error in aes_demo (line 50)
plaintext1 = plaintext( 16*(i-1)+1:16*(i-1)+16);
%AES_DEMO Demonstration of AES-components.
%
% AES_DEMO
% runs a demonstration of all components of
% the Advanced Encryption Standard (AES) toolbox.
%
% In the initialization step the S-boxes, the round constants,
% and the polynomial matrices are created and
%AES_DEMO Demonstration of AES-components.
%
% AES_DEMO
% runs a demonstration of all components of
% the Advanced Encryption Standard (AES) toolbox.
%
% In the initialization step the S-boxes, the round constants,
% and the polynomial matrices are created and
% an example cipher key is expanded into
% the round key schedule.
% Step two and three finally convert
% an example plaintext to ciphertext and back to plaintext.
% Copyright 2001-2005, J. J. Buchholz, Hochschule Bremen, [email protected]
% Version 1.0 30.05.2001
% Initialization
[s_box, inv_s_box, w, poly_mat, inv_poly_mat] = aes_init;
% Define an arbitrary series of 16 plaintext bytes
% in hexadecimal (string) representation
% The following two specific plaintexts are used as examples
% in the AES-Specification (draft)
% plaintext_hex = {'00' '11' '22' '33' '44' '55' '66' '77' ...
% '88' '99' 'aa' 'bb' 'cc' 'dd' 'ee' 'ff'};
%plaintext_hex = {'32' '43' 'f6' 'a8' '88' '5a' '30' '8d' ...
% '31' '31' '98' 'a2' 'e0' '37' '07' '34'};
% % x = fopen('D:\MATLAB\AES\Aa.txt', 'r');
%
%
% %
% a = a(1:16);
% size(a);
[plaintext1,fs]= wavread('A1.wav','native');
plaintext1=plaintext1(1:16);
plaintext_hex=dec2hex(plaintext1);
plaintext = hex2dec (plaintext_hex);
for i = 1:8172/16;
size = length (i/16);
if (size > plaintext1)
plaintext = plaintext(16*(i-1)+1 :16*(i-1) + 16);
else
disp ('encrypted values');
end
end
% Convert plaintext from hexadecimal (string) to decimal representation
% This is the real McCoy.
% Convert the plaintext to ciphertext,
% using the expanded key, the S-box, and the polynomial transformation matrix
ciphertext = cipher (plaintext, w, s_box, poly_mat, 1);
% Convert the ciphertext back to plaintext
% using the expanded key, the inverse S-box,
% and the inverse polynomial transformation matrix
re_plaintext = inv_cipher (ciphertext, w, inv_s_box, inv_poly_mat, 1);
this is my aes demo file i have made changes but till its not working please do help me
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