Right :-)
Maybe such an example would be helpful in the documentation to help
others not to make the same mistake?
Ingo Naumann wrote:
Your example shows quite nicely why you MUST NOT re-use IVs when
applying CFB mode. If you do -- security is gone.... I.
On Thu, Feb 18, 2010 at 11:51 AM, Roland Bock <[email protected]> wrote:
Hi,
after reading this http://www.pvv.org/~asgaut/crypto/thesis/node16.html I
understand: Encryption is performed Byte by Byte. In that case, the result
is as expected.
Thank you for your patience :-)
Regards,
Roland
Roland Bock wrote:
So, yes, if the IV (which is used in place of the "previous ciphertext
block" for the first message block) and message blocks up to a certain point
are identical, the ciphertext will be to that point as well, and the XOR
output for the next block will differ exactly where the bits of the next
message block differ. This is why you need to pick different IV values per
message.
Hi, yes, I am aware of this, and I would agree if I encrypted, say, 10
blocks with the first 9 being identical. In that case, of course, the first
9 encrypted blocks of the ciphertext would be identical.
But I encrypted several texts of 4Bytes (much less than one block) which
differ in just the last Byte. I don't think that they should result in
output which also differs in just the last Byte.
Using CBC, btw, I get completely different results for very similar input.
This is what I would expect. It is padded to the block size, though.
Regards,
Roland
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