Talk:Padding (cryptography)

Matt,

Padding is, in some sense, a higher genus of thing than both whitening and use of an IV. I was attempting to use the reference to both here as 1) an invitation to follow the link and learn something and 2) an attempt to make clear that -- at least conceptually -- both are additions (in principle arbitrary) to plaintexts or keys and so something of the same type, however different the details.

I don't see the generalisation. As I understand it, "padding" is an extension of the length of a message, such as "CAT" -> "CATXX". "Whitening" refers to scrambling the plaintext using a binary group operation with a subkey at either the initial or final round of an iterated block cipher. They are unrelated concepts, unless there's a different usage that I'm not aware of. Initialisation vectors are similarly unrelated conceptually, but I reckon its worth a "see also" since both are details that crop up when using block cipher modes.

Padding can be, and I recall that it was, used at both ends, and in the middle for that matter, of messages. In fact, Russian copulation was used as a sort of padding (though this is a stretch since no data is added) to move stereotyped ending/beginnings away from ends and begins. Not so important now when redundancy can be very effectively removed by routine use of compression. My memory of whitening differs, but... The article is looking more necessary, isn't it?

Ah, OK. (The definition I'm familiar with is noted in Schneier's Applied Cryptography, Section 15.6, if you have it to hand...) — Matt 23:43, 12 Apr 2004 (UTC)

A whitening article was, I suppose, in my future after some looking up of details I can't trust my memory to supply with fidelity. Sigh.

Go for it; I included a link from the Camellia article with that intention.

OK. But I will be taking a while with it, as I clearly can't just do it out of my head.

I suggest we reinstall mention of both whit and IV, with suitable notations as to the details of usage and such.

I think separate articles would be better.

Separate articles would indeed be good, and are obviously necessary; one exists (apparently) for IV, but I disagee that they shouldn't be mentioned here. If whitening has the meaning I thought it did. If it's your meaning, it obviously shouldn't be included here.

You might be interested to hear that I have finally had a penny drop. Seems like it took long enough. Many of the differences between you and I seem to be based in our attitude toward the reader. I keep always foremost in mind that the reader will be looking not only for facts but, being unfamiliar with the territory in many (most, nearly all, every?) case, and will benefit from explanation you deem surplus. Does this seem so to you as well? If so, do you have any suggestions as to how we might hit some middle ground on this dimension? ww 20:32, 12 Apr 2004 (UTC)

I agree that explanation that aids comprehension is good. However, some explanation can be extraneous and actually detract from the reader's understanding. I think we often disagree on what the reader is looking to find out, particularly in the encyclopedia vs textbook thing. — Matt 21:12, 12 Apr 2004 (UTC)

I guess the divergence is with 'extraneous', and with expository planning. I tie, or try to, things together to make easier the reader's road to understanding. More connections, more ways to see how things relate, more mental links, and perhaps a greater chance to understand them. Your style/inclination has fewer connections between concepts and forces the reader to do more conceptual contstruction.

I don't think the difference is textbook vs encyclopedia; even at my most extraneous, my work here is unsuited to a textbook. Having written one or two, I can speak with some authority on the inadequacy of my work here in re use in/part of textbooks.

We really should find a compromise on this, if this is the core of divergence, or you'll keep editing out my extraneous, and all will be uncomfortable. I need my extraneous to stay healthy! Seriously, at least for the occasional humourous aside, see Wetman's discussion of the place of humor here at his user page.

ww 22:44, 12 Apr 2004 (UTC)