Hello and thanks for providing us such a great and useful tool,
I would like to have some details about the way the data is encrypted through AESCrypt.
What is the mode of operation used ?
What about the padding method in case the messages are not a multiple of the block size ?
Thank you for your answer,
Kindly,
GCerto
Encryption Method Details
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paulej
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Re: Encryption Method Details
AES Crypt uses AES with a 256-bit encryption key. It uses the the CBC mode:
http://en.wikipedia.org/wiki/Block_ciph ... _.28CBC.29
It also uses an HMAC to ensure messages are not tampered with:
http://en.wikipedia.org/wiki/Hmac
AES works on a 16-bytes (128 bit) block. If the final block is less than 16 octets, AES Crypt still writes out the entire 16 octets of cipher text, but it inserts a 4-bit value modulo that indicates how many octets are truly present in final block of the original file. This ensures that AES Crypt will reproduce the correct file size.
Note that the HMAC was intended to also be calculated over the modulo bits, but we failed to do that when writing the code. As such, somebody could alter those modulo bits in the cipher text file and cause AES Crypt to produce a file that is slightly longer or shorter when decrypted (from 1 to 15 octets). It does not compromise the security of the protected information, but it is a point of frustration if somebody hacks your .aes files. This will be corrected in the next major release of AES Crypt.
http://en.wikipedia.org/wiki/Block_ciph ... _.28CBC.29
It also uses an HMAC to ensure messages are not tampered with:
http://en.wikipedia.org/wiki/Hmac
AES works on a 16-bytes (128 bit) block. If the final block is less than 16 octets, AES Crypt still writes out the entire 16 octets of cipher text, but it inserts a 4-bit value modulo that indicates how many octets are truly present in final block of the original file. This ensures that AES Crypt will reproduce the correct file size.
Note that the HMAC was intended to also be calculated over the modulo bits, but we failed to do that when writing the code. As such, somebody could alter those modulo bits in the cipher text file and cause AES Crypt to produce a file that is slightly longer or shorter when decrypted (from 1 to 15 octets). It does not compromise the security of the protected information, but it is a point of frustration if somebody hacks your .aes files. This will be corrected in the next major release of AES Crypt.