I'm implementing AES encryption. During the mix column/inverse mix columns procedures, I need to do Galois field multiplication. I'm using the look-up tables in the following document(Section 5.4.2)
https://www.ime.usp.br/~rt/cranalysis/AESSimplified.pdf
If you go to the section specified above, the (0,0) column in the L table is empty. So what do I return when say I need to look up L(0,0). I tried to return 0, but that's giving me the wrong encryption.
The original action is multiplication. Therefore, if your value is 0x00 you don't have to look it up in the L table, and the result of the whole multiplication is zero.
Related
I am using PCA from sklearn for data reduction with 27 features and 3558 rows data and I got the following result
I have read a lot of articles but they just explain the correlation between variables and each principal component (loadings), but here I want to know what does negative and positive value means in each cell (PC1 PC2 PC3) in each data row in the final result?
You can't really deduce much from the sign of a value in the principal components. Remember that the principal components are linear combinations of initial features. Thus, a negative component just means that a linear combination gave a negative number. For example you could have the first component equal to 5*feature_1-7*feature_2=x where x<0.
Not sure what you are trying to achieve here but if you want to understand more deeply what those components mean, I suggest to look at the code at the very bottom of this page.
Negative value means the component is not significant.
Positive value means the component is significant.
My issue is that I need to reference a cell (A1) which will either be the name of a state that can be found in column L, or it can be "All States" which I then want to include all results of column L. I can't work out how to include this.
=SUMPRODUCT(--(IF(A1="All States",Data!$L:$L,Data!$L:$L=A1)),Data!Q:Q)
I want to add a bunch more criteria based on the above so I don’t want to go down the route of imbedding the sumproduct in an if function because the formula will quickly become too unweildy.
You have a lot of choices. Using your initial formula I would tweak it to
(A) =SUMPRODUCT((IF($A$1="All States",1,($L$2:$L$11=$A$1)))*($Q$2:$Q$11))
But this would need to be entered as an array formula so instead of just confirming with ENTER, you need CONTROL+SHIFT+ENTER. You will know you have done it right when { } show up around your formula. Note that they cannot be added manually.
A non array type formula which would be faster I believe would be to look at your two options. You are either dealing with a single state or all states. Set up an IF check to determine if you need to sum all of column Q, or if you need to find a single value from column Q. I used the following formula:
(B) =IF(A1="all states",SUM($Q$2:$Q$11),INDEX($Q$2:$Q$11,MATCH($A$1,$L$2:$L$11,0)))
A bit of a cheat but but simplifies things, is to add a final state to the bottom of your list in L and call is "All States". In the corresponding row in Q place =sum(First Cell:Last Cell). If you do that then you can use the following formula:
(C) =SUMPRODUCT(($L$2:$L$12=$A$1)*($Q$2:$Q$12))
That are other options out there as well, just thought I would show some options.
I am trying to compare the numerical data in two columns in Google Sheets (say, Col. A and B) and return a count of all of the times that they vary by say, more than 1 (e.g., if A3 = 5 and B3 = 2, this should get counted). The two-column arrays will always be of equal size.
At first, I thought that either COUNTIF or COUNTIFS would be my go-to tool, but I can't get this to work with either formula. These formulas seem to handle criteria within a cell, but - as far as I can tell - can't handle criteria comparing data within two different (adjacent) cells.
Can someone help me with some super syntax work-around to get COUNTIF/COUNTIFS to work... or is there a more appropriate formula to the job (perhaps involving FILTER)?
*Quick Edit: I know I could always add an additional column, which would be very simple in this example. But my real-world spreadsheets are a lot more complex and are already suffering from column overload. A lot of other formulas are already set up around existing columns, and I was hoping to discover a more elegant solution that would allow me to come up with the count without having to add a new column for each and every comparison calculation.
=ARRAYFORMULA(IF(LEN(A:A&B:B), IF(A:A-B:B>1, 1, )+IF(B:B-A:A>1, 1, ), ))
if you want final sum instead of "per row" count use:
=SUM(ARRAYFORMULA(IF(LEN(A:A&B:B), IF(A:A-B:B>1, 1, )+IF(B:B-A:A>1, 1, ), )))
Add a third column, containing e.g. =ABS(SUM(A3-B3)). (The ABS gives you the positive difference regardless of which value is larger.)
At the bottom of that column, use COUNTIF like =COUNTIF(C1:C25, ">1") (where C1:C25 is the range of cels containing those positive differences).
I have a mapping Nx2 between two set of encodings (not relevant: Unicode and GB18030) under this format:
Warning: huge XML, don't open if having slow connection:
http://source.icu-project.org/repos/icu/data/trunk/charset/data/xml/gb-18030-2000.xml
Snapshot:
<a u="00B7" b="A1 A4"/>
<a u="00B8" b="81 30 86 30"/>
<a u="00B9" b="81 30 86 31"/>
<a u="00BA" b="81 30 86 32"/>
I would like to save the b-values (right column) in a data structure and to access them directly (no searching) with indexes based on a-values (left column).
Example:
I can store those elements in a data structure like this:
unsigned short *my_page[256] = {my_00,my_01, ....., my_ff}
, where the elements are defined like:
static unsigned short my_00[256] etc.
.
So basically a matrix of matrix => 256x256 = 65536 available elements.
In the case of other encodings with less elements and different values (ex. Chinese Big5, Japanese Shift, Korean KSC etc), I can access the elements using a bijective function like this:
element = my_page[(unicode[i]>>8)&0x00FF][unicode[i]&0x00FF];, where unicode[i] is filled with the a-like elements from the mapping (as mentioned above). How do I generate and fill the my_page structure is analogous. For the working encodings, I have like around 7000 characters to store (and they are stored in a unique place in my_page).
The problem comes with the GB18030 encoding, trying to store 30861 elements in my_page (65536 elements). I am trying to use the same bijective function for filling (and then accessing, analogously) the my_page structure, but it fails since the access mode does not return unique results.
For example: For the unicode values, there are more than 1 element accessed via
my_page[(unicode[i]>>8)&0x00FF][unicode[i]&0x00FF] since the indexes can be the same for i and for i+1 for example. Do you know another way of accessing/filling the elements in the my_page structure based only on pre-computed indexes like I was trying to do?
I assume I have to use something like a pseudo-hash function that returns me a range of values VRange and based on a set of rules I can extract from the range VRange the integer indexes of my_page[256][256].
If you have any advice, please let me know :)
Thank you !
For GB18030, refer to this document: http://icu-project.org/docs/papers/gb18030.html
As explained in this article:
“The number of valid byte sequences -- of Unicode code points covered and of mappings defined between them -- makes it impractical to directly use a normal, purely mapping-table-based codepage converter. With about 1.1 million mappings, a simple mapping table would be several megabytes in size.”
So most probably is not good to implement a conversion based on a pure mapping table.
For large parts, there is a direct mapping between GB18030 and Unicode. Most of the four-bytes characters can be translated algorithmically. The author of the article suggests to handle them such ranges with a special code, and the other ones with a classic mapping table. These characters are the ones given in the XML mapping table: http://source.icu-project.org/repos/icu/data/trunk/charset/data/xml/gb-18030-2000.xml
Therefore, the index-based access on Matrix-like structure in C++ can be a problem opened for whom wants to research on such bijective functions.
My users will in some cases be able to view a web version of a database table that stores data they've entered. For various reasons I need to include all the stored data, including a number of integer flags for each record that encapsulate adjacencies and so forth within the data (this is for speed and convenience at runtime). But rather than exposing them one-for-one in the webview, I'd like to have an obfuscated field that's just called "reserved" and contains a single unintelligible string representing those flags that I can easily encode and decode.
How can I do this efficiently in C++/Objective C?
Thanks!
Is it necessary that this field is exposed to the user visually, or just that it’s losslessly captured in the HTML content of the webview? If possible, can you include the flags as a hidden input element with each row, i.e., <input type=“hidden” …?
Why not convert each of the fields to hex, and append them as a string and save that value?
As long as you always append the strings in the same order, breaking them back apart and converting them back to numbers should be trivial.
Use symmetric encryption (example) to encode and decode the values. Of course, only you should know of the key.
Alternatively, Assymetric RSA is more powerfull encryption but is less efficient and is more complex to use.
Note: i am curios about the "various reasons" that require this design...
Multiply your flag integer by 7, add 3, and convert to base-36. To check if the resulting string is modified, convert back to base-2, and check if the result modulo 7 is still 3. If so, divide by 7 to get the flags. note that this is subject to replay attacks - users can copy any valid string in.
Just calculate a CRC-32 (or similar) and append it to your value. That will tell you, with a very high probability, if your value has been corrupted.