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(male narrator) So now we're gonna encrypt the message:
"Meet at First and Pine at midnight,"
using a transposition cipher with rows eight characters long.
Specifically, we're gonna be using
a tabular transposition cipher.
Now a transposition cipher means
that instead of changing what the letters are,
like we do with substitution ciphers,
we're just gonna change the order
in which the characters appear.
In this case, we're gonna use rows and columns
and change the way we read them.
So what we're gonna do
is we're gonna write out this message
eight characters at a time.
So we're gonna write: meet...at...first...
What do we got:
one, two, three, four, five, six, seven, uh...eight...
[humming]
Notice, I'm leaving out, uh...
I'm leaving out the, um...the spaces.
And normally, I would, uh...do this
using all uppercase characters, uh...there we are.
So...meet at First and Pine at midnight.
Uh...notice we got a few spaces left here,
and so normally, we would, uh...pad the message,
which means make up some random characters.
So maybe I'll put...add a P, X, and an R in here,
uh...in order to fill it out.
So that is our message jotted down.
Now to create our encrypted text,
we are going to read... we're gonna rewrite the message
reading down the columns instead of across the columns.
So our encrypted message will be...
Right, again, I'm reading down the columns here,
so next, we're gonna have...
[laughs] And I'm gonna have to continue down here, uh...
And now, it would be really important here
to either eliminate all the spaces
or reposition the spaces
to hide the size of the table used,
because in this particular method,
this information is the encryption key.
That's the information you need to know
in order to either encrypt or decrypt the message.
Now notice that means
that we don't have a lot of encryption keys here,
unless if we had a really long message
and could change this quite a bit.
Um...but there are other versions of this encryption,
where instead of reading down the columns,
we could read up the columns,
or we could read diagnolly along the columns,
or we could read in a little spiral pattern.
So there are other, uh...versions
of this type of encryption that we could do.
Okay, so now let's see if we can decrypt a message the same way.
So in this case,
uh...because we note that this was created
using a transposition cipher with 20 characters long,
the first thing we need, uh... with rows five characters long.
The first thing we need to know
is how many total characters do I have here?
Uh...and in this case, I have 20 characters,
and if each row is five characters long,
that means I had four rows.
So now remember, this text came from the column,
and so to decrypt this,
I'm gonna write C, E, E, I down the first column.
And remember, I just figured out that there's four rows,
so I know to do it in groups of four.
So now I'm gonna continue this for the rest of the message.
And there we go.
Now that we have it written out in columns,
we can decrypt the message by reading across the rows.
So it looks like we've got: call me...call me...in...
T, H, E...the...morn-ing... morning.
And it looks like we got
a couple extra letters here-- V, W--
which are probably those padding characters
used to fill out the table.
So it looks like our encrypted message was,
"Call me in the morning."