Schedule

We meet TTh, 2:30 - 3:45 pm, in Bartlett 310

WEEK 7 Games

M 6 March What Bob Said to Alice

• Read Singh, chapters 7 and 8 (as much as you can).
• Here's Singh's television show on the subject.
• Some perl programs.

 

W 8 March Crypts of Crypts

• Here is a list of the SYSTEM TEAMS.
• Browse Jim Waldo on system design.
• Here are the Apple Human Interface Guidelines
• Some perl programs.
• Browse How to program (with perl) book [free via UMass]; here is an advanced perl "cookbook" [via UMass]
• Unsolved: Voynich (Wiki, the full manuscript, an article)

ALSO: FBI cyber division page; NSA Crytpo Museum (with on-line histories)

Perl programs for Caesar Shifts:

Encrypt

#! usr/bin/perl -w

# Let's declare our variables.

my $CT = "";
my $cShift = 0;
my $i = 0;
my $length_of_crypt = 0;
my @letter;
my $thisLetter = "";
my $thisLetterASCII = 0;

# First, we need to get the crypt. So, let's ask the user for it.

print "\nEnter crypt: ";

# Now, we need to take the user's input and place in tinside a variable.
# Let's call the variable CT for cipher-text. It must start with a dollar sign.

$CT = <STDIN>;

# We don't know what sort of nonsense the user might have typed. So we'll
# check it. Get rid of unwanted characters, punctuation, and spaces.
# We'll use the substitute function. s/x/y/ substitutes y for every x
# The character \W means everything that is not an alphanumeric

$CT =~ s/\W//gi;

# Now get rid of numbers

$CT =~ s/\d//gi;

# Now get rid of spaces

$CT =~ s/\s//g;

# Let's put the crypt into capital letters to make it consistent

$CT = uc($CT);

# Let's ask how much of a shift the user wants, not forgetting a new line

print "\nHow much of a Caesar Shift?: ";
$cShift = <STDIN>;

# Let's make sure it's a number and be curt about it

if ( $cShift =~ m/[0-9]+/)
{
if ($cShift > 25) {$cShift = 2; print "\nNot funny. Setting it to 2." }
}
else
{
print "\nNot a number. Goodbye.";
}

# Now, let's find out how many letters are in the crypt.
# That way, we can loop through the crypt and ceasar shift each letter

$length_of_crypt = length ($CT);

# Time to put each letter into a different variable. We'll use an array

@letter = split //, $CT;

# now, let's loop through every letter, change it to ASCII, add the shift
# and turn it back into a letter

for ($i=0; $i < $length_of_crypt; $i = $i +1)
{

$thisLetterASCII = ord($letter[$i]);
$thisLetterASCII = $thisLetterASCII + $cShift;
print chr($thisLetterASCII);

}

# clean up

print "\n";

_________________________

Decrypt

#! usr/bin/perl -w
# deshift a Caesar

my $CT = "";
my $cShift = 0;
my $i = 0;
my $length_of_crypt = 0;
my @letter;
my $thisLetterASCII = 0;
my $check = 0;
my $over = 0;

print "\nEnter crypt: ";

$CT = <STDIN>;

$CT =~ s/\W//gi;
$CT =~ s/\d//gi;
$CT =~ s/\s//g;
$CT = uc($CT);

$length_of_crypt = length ($CT);

@letter = split //, $CT;

for ($cShift = 0; $cShift < 26; $cShift = $cShift + 1)
{

for ($i=0; $i < $length_of_crypt; $i = $i + 1)
{
$thisLetterASCII = ord($letter[$i]);
$check = $thisLetterASCII + $cShift;
if ($check > 90)
{ $over = $check - 90;
$thisLetterASCII = 64 + $over;
}
else
{
$thisLetterASCII = $thisLetterASCII + $cShift;
}
print chr($thisLetterASCII);
}
print "\n";
}