[Cryptography Team] block-based cipher padding

[Ron Teitelbaum]

Hi Chris,

 

I've finally figured out what was going wrong with some of my CBC tests.  I
have some more questions about padding.

 

The test: 

 

            Case #3: Encrypting 48 bytes (3 blocks) using AES-CBC with
128-bit key

            Key : 0x6c3ea0477630ce21a2ce334aa746c2cd

            IV : 0xc782dc4c098c66cbd9cd27d825682c81

            Plaintext : This is a 48-byte message (exactly 3 AES blocks)

            Ciphertext: 0xd0a02b3836451753d493665d33f0e886

            2dea54cdb293abc7506939276772f8d5

            021c19216bad525c8579695d83ba2684

 

Is returning the value:
'D0A02B3836451753D493665D33F0E8862DEA54CDB293ABC7506939276772F8D5021C19216BA
D525C8579695D83BA2684D248B3E0F2388C137102846EB06272FF'  which is correct
except for the padding.  Since we are using the padding and it will be
removed in our system should this be considered a passing test?

 

My guess is yes but if we send these encrypted values to other systems will
they know how to un-pad and decrypt the cipherText?  In other words, how
widely adopted is Schneier's and Ferguson's padding suggestion?  Should we
enable a switch to allow developers to turn this off? 

 

Ron Teitelbaum

President / Principal Software Developer

US Medical Record Specialists

Ron at USMedRec.com 

Squeak Cryptography Team Leader

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