How do to handle the case, when the string to be encrypted using AES is less than 16 bytes?
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Sunil
am 23 Mai 2014
Kommentiert: Geoff Hayes
am 2 Jul. 2021
AES code requires the string to be 16 bytes. How do I handle a case, when the string to be converted is less than 16 bytes both during encryption and decryption? Appreciate, if you could paste the code snippet?
Thanks a lot!
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Geoff Hayes
am 23 Mai 2014
Bearbeitet: Geoff Hayes
am 23 Mai 2014
If the string (to encrypt) is less than 16 bytes, then why not just pad with zeros? Looking at the documentation referenced from your above link ( http://buchholz.hs-bremen.de/aes/AES.pdf) the plaintext input to the cipher function is just an array of 16 doubles (presumably, the software only considers the first 8 bits from each double) converted from the plaintext string via hex2dec. So you could do something like the following with your plaintext hexadecimal string:
ptLen = length(plaintext); % get the length of the plaintext string
if ptLen>0 && ptLen<16
plaintext = [plaintext repmat({'00'},1,16-ptLen)]; % pad the plaintext
end % string with zeros
Now your plaintext string has length of 16, and the conversion from hexadecimal to decimal, and the encryption can proceed (as per the documentation).
The decryption shouldn't matter as the cipher text will be 16-bytes (I'm assuming this given my brief read of the document).
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Geoff Hayes
am 2 Jul. 2021
Anis - I think that would would encrypt every block of 16 bytes and then, when you have a block that is less than 16 bytes, pad it with zeros. Perhaps.
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