Recently Asked Questions
in Math 502

1. Q. Will all the code files be available on the T drive?

   A. Yes.

2. Q. I would like to understand whether the block size specified in "sqvec" must be set larger than the highest value in a string of ASCII codes which has been shifted prior to encryption. In other words, if a vector of ASCII codes has been shifted n digits before encryption, should the block size be greater than (127+n)?

   A. Note that the first argument of “sqvec” is supposed to be a vector of digits in base b, where b is the second argument. So sqvec(v,2,3) converts a vector of digits in base 2 to a vector of digits in base 2^{3} = 8. If by “block size” you mean the third argument, the answer to your question is no. If, on the other hand, it refers to the second argument, then the answer is yes.

   Note, however, that “sqvec” is not, strictly speaking, useful for general base conversions since it “pads” its first argument with trailing 0's so that the number of components is a multiple of the block size specified in the third argument.

   Do the following illustrations cover your question? If not, please try to restate your question in a more specific way.

   > v:=convert(40487,base,2);

                  v := [1, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1]

    

   > sqvec(v,2,3);

                                   [7, 1, 0, 7, 4, 4]

    

   > w:=convert(40487,base,3);

                           w := [2, 1, 1, 2, 1, 1, 1, 0, 0, 2]

    

   > sqvec(w,2,3);

   Error: term 2 (seq. 1) not a digit in base 2

    

   > x:=convert(``test string'', bytes);

               x := [116, 101, 115, 116, 32, 115, 116, 114, 105, 110, 103]

    

   > xs:=vshift(x,-30);

                    xs := [86, 71, 85, 86, 2, 85, 86, 84, 75, 80, 73]

    

   > xsq:=sqvec(xs,97,2);

                       xsq := [8413, 8331, 279, 8426, 7355, 7081]

    

   > convert(vshift(exvec(xsq,97,2),30),bytes);

                                      ``test string''