> I guess sort of intuitively (I'm not a cryptographer):
Don't worry. I'm not one either. And I think that's why I am actually able to tell you that invertibility / 1-to-1 onto bijections is an important concept :-)
An actual cryptographer would tell you its 1-to-1 and onto and move on.
> It's a thing I don't love about illustrations like the one we're discussing, in that it sort of presents this "intelligent design" problem of, like, "how did we arrive at this incredibly complex fully functioning eyeball", when there's a whole series of smaller evolutionary steps that led to this point; it's more productive maybe to look at the bones of the whole design before diving into the details of which bits go where at each precise step.
Agreed. There's a lot of history here, and knowing all of the history helps a _LOT_.
Go back 50 years ago, and ciphers are way easier to grok. DES / Feistel ciphers are really easy for example. But then we discovered issues about them and iteratively improved.
The old "DES" / Feistel cipher principles of confusion and diffusion remain with us today, but each step has been honed for 90s-era computers (SBoxes and 32-bit numbers), and then honed again for 2010s-era computers (recognition that XOR / Rotate / Add is a faster primitive today than memory-based SBoxes).
I don't think any of the principles have changed since DES / Feistel cipher days. Its just that today's designs are better for today's computers.
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EDIT: As far as I can tell: "confusion" can be created by (data) XOR (rotate-data) XOR (rotate-data) primitives. "diffusion" can be created by the "ADD" operator (in particular: "carries" will diffuse the bits around).
So XOR, rotate, and Add are the only primitives you need to make a modern crypto-cipher. All three primitives are outrageously fast on modern machines.
AES and other older ciphers tried to make each round relatively high quality. Modern ciphers try to make each round low-quality, and then do something like 64-rounds or 80-rounds to make up for it.
So you'll see old ciphers like AES with just 11 rounds, but modern ciphers / crypto algorithms like SHA256 use 64-rounds.
Don't worry. I'm not one either. And I think that's why I am actually able to tell you that invertibility / 1-to-1 onto bijections is an important concept :-)
An actual cryptographer would tell you its 1-to-1 and onto and move on.
> It's a thing I don't love about illustrations like the one we're discussing, in that it sort of presents this "intelligent design" problem of, like, "how did we arrive at this incredibly complex fully functioning eyeball", when there's a whole series of smaller evolutionary steps that led to this point; it's more productive maybe to look at the bones of the whole design before diving into the details of which bits go where at each precise step.
Agreed. There's a lot of history here, and knowing all of the history helps a _LOT_.
Go back 50 years ago, and ciphers are way easier to grok. DES / Feistel ciphers are really easy for example. But then we discovered issues about them and iteratively improved.
The old "DES" / Feistel cipher principles of confusion and diffusion remain with us today, but each step has been honed for 90s-era computers (SBoxes and 32-bit numbers), and then honed again for 2010s-era computers (recognition that XOR / Rotate / Add is a faster primitive today than memory-based SBoxes).
I don't think any of the principles have changed since DES / Feistel cipher days. Its just that today's designs are better for today's computers.
------
EDIT: As far as I can tell: "confusion" can be created by (data) XOR (rotate-data) XOR (rotate-data) primitives. "diffusion" can be created by the "ADD" operator (in particular: "carries" will diffuse the bits around).
So XOR, rotate, and Add are the only primitives you need to make a modern crypto-cipher. All three primitives are outrageously fast on modern machines.
AES and other older ciphers tried to make each round relatively high quality. Modern ciphers try to make each round low-quality, and then do something like 64-rounds or 80-rounds to make up for it.
So you'll see old ciphers like AES with just 11 rounds, but modern ciphers / crypto algorithms like SHA256 use 64-rounds.