The Side Channel

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1:52 PM

I need to see if can make my AES hardware document public. It would answer a lot of these AES questions as you can just reference where it works/why it works via a Figure.

SEJPM

@bdegnan is there fancy graphics beyond what is in FIPS-197?

b degnan

yeah, it's circuit's based that shows everything. It's basically at 10x longer version of this: github.com/bpdegnan/aes/blob/master/aes-sbox/documentation/…

I never got it through the release approval process as the funding ended abruptly. (the project got canned with 2 days notice. :/ )

SEJPM

I'm not sure whether everyone will be more happy with HW diagrams :p

b degnan

well, yeah, but that's how the lego make the spaceship!

but questions like this: crypto.stackexchange.com/questions/77800/…

I can answer easily with just referencing the Figure as all hardware is basically byte sliced due to the 8-bit s-box

SEJPM

oh yeah, questions on bit- / byte-slicing definitely profit from a hardware mindset

kelalaka

2:28 PM

I don't see a very deep figures there.

b degnan

3:00 PM

I'll see if I can get the complete document released. (it takes 10 forms and 6mo as it was part of my NSA work. :/ )

kelalaka

If they accept.

Jonathan Hutton

Quick question if that is possible for me.... I've heard correctly said that randomness is the first test of a ciphertext. If it is not random it is flawed and will eventually be exploited..... But if a ciphertext has no randomness wouldn't the opposite be just as true and be impossible to decrypt without the key.

Maarten Bodewes

@JonathanHutton It should not be random, it should be indistinguishable under chosen plaintext. As you probably also want to keep the ciphertext as small as possible, the randomness requirement kind of follows from that...

Jonathan Hutton

3:48 PM

@MaartenBodewes Thank you for clarity, i have seen others make that same statement. A subtle but important difference between the indistinguishable and random.

2 hours later…

b degnan

6:09 PM

@JonathanHutton The nuance is due to the fact that you have a "series" of blocks in a cipher. If you have the same data, let's say all 0's over and over, your stream will not be random. This is where the counter modes come in. Ideally, if you had a counter from 0 to 1024, and you encrypted 0, you would see a random stream on the output.

Block cipher mode of operation

In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. A block cipher by itself is only suitable for the secure cryptographic transformation (encryption or decryption) of one fixed-length group of bits called a block. A mode of operation describes how to repeatedly apply a cipher's single-block operation to securely transform amounts of data larger than a block.Most modes require a unique binary sequence, often called an initialization vector (IV), for each encryption operation. The IV has...

Jonathan Hutton

6:51 PM

@bdegnan i certainly understand. I was not understanding scale context. But as applied to block cipher mode.... of course.

2 hours later…

Crypto HNQ

9:11 PM

Q: Why does Encrypt-Then-Sign not yield a CCA-secure public-key encryption scheme?

In symmetric cryptography, combining an IND-CPA secure symmetric encryption scheme with a secure MAC with the encrypt-then-MAC method yields a IND-CCA secure symmetric encryption scheme. I am trying to understand why this does not hold in the asymmetric case. Suppose you have an IND-CPA secure pu...