Hello Julius,

I can't comment on most of your notes, but at least I have something
to say about this one:

> I'm also curious why CFB
> and OFB mode always  result in "NoPadding", whereas CBC and ECB result in
> "PKCS5Padding".

It's been a decade that I had to do with it, so I can't explain all
the details by heart. ECB stands for Electronic Code Book, where each
block is encrypted individually. That requires padding to block size.
CBC is Cypher Block Chaining, each encrypted block is fed back into
the next block of data to be encrypted. Again, padding to block size
is required. CFB is Cypher FeedBack, OFB is Output FeedBack. One of
them doesn't even consider the data to be encrytped. It just keeps
on encrytping and re-encryting an initial value like a random number
generator. These random numbers are then XORed to the plain text.
While the loop for generating the random numbers always works with
block size, there is no problem in just taking a part of that block
when XORing, so no requirement for padding the input. I don't remember
the details of the last one, but it also uses a strategy that does not
require padding of the input data.

Since "Applied Cryptography" is a very expensive book, I recommend
Wikipedia for a more detailed description:
http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation


cheers,
  Roland

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