Time
10 hours 28 minutes
Difficulty
Advanced
CEU/CPE
15

Video Description

This lesson discusses streams, which is a type of symmetric cipher. Stream ciphers can work via scrambling characters, shifting them left or right. This is also known as transposition. Another method is substitutions. There is also a method called XOR which uses the key bit by bit to provide encryption.

Video Transcription

00:04
all right. So we just talked about symmetric blocks like this, how they choked at and walks and operate on a block. At the time. The other type of symmetric ciphers, called a stream
00:15
and a strain works on a single bit of it encrypts very, very fast. As a matter of fact, it's really best incorporated with barbed wire mechanisms,
00:28
because what happens is to take advantage of speaking the harbor device that just spit out once and zeros quickly, quick.
00:36
Okay, now with your stream size is getting one bit of the time. And there are a couple of different ways that stream ciphers can work. A common way is transposition, and transposition is scrambling to care, you know, shifting the characters left or right
00:53
straight with them. So, for instance, if the word was the
00:57
train's position, it might be HT, for instance, so scrambling the characters
01:04
substitution pure substitution is replacing one character with nothing,
01:10
and a lot of times we want multiple substitution, multiple trans positions. But then there's also a process called X four and X, or stands for exclusive. Or let me just show you how ex war works X for
01:27
So the way explore works is let's just say I've got some plain tax and once again that plain text will be a series of ones and zeros. And then I'm gonna have a pseudo bravely generated key
01:40
and again, I just randomly make leads up.
01:42
But with this particular encryption mechanism again, it's a stream. So what it does uses the key, it bit by bit to providing.
01:53
It's actually fairly easy, because when you match up the plain text with key,
02:00
where the values are alike,
02:02
the cipher text become serious.
02:06
Where the values are different, side cash becomes one.
02:10
So I, following this rule, play Texas one that he is zero. Those were different values. So the cipher comes.
02:20
These values are the same serum, a different one
02:23
different, one different, one
02:28
saying zero
02:30
different
02:31
same serum. So this is a very quick process called exploring. But what it does is it provides encryption bit by bit by bit and a lot of algorithms that air stream ciphers. Many of them use that
02:46
the most common stream cipher is one called Arcee, and this is used by our wireless calls. Wept in W p. A.
02:59
Not W P. A to,
03:01
but, uh, what happened? W p A. And you could see how very fast this was to provide encryption. You take the key matchup that I've been with playing Paxton to Values are different yet Cipher text 12 values say cipher text
03:17
so very quick to encrypt. But also, if you have the key, it's very quick to decrypt because if you just match the cipher key, well, those were different. It's gotta be one.
03:30
There's a difference. Can be won
03:31
different, different ones saying zero. So it's very quick to encrypt is very quick to decrypt, and that's a real advantage of RC four. However, when we gain speed, a lot of times we trade security. So RC four is not considered near Lee's here
03:51
as a block cipher. Like eight. Yes, and as a matter of fact, I just said Weapon W P. A. Usar C. Four. When we went to W p. A. To which is really
04:02
the Wildfire protocol, we wanted to get to
04:04
w G eight to It's a big change. Is it going to advance Encryption State 80 s a block cipher that's stronger and more secure, and that's a big step in the right direction.
04:17
So that's your stream, ciphers. Very fast. The Onley Stream cipher. You would need to know for this examines RC four.
04:27
Hey there other RC subs or two and three and five and six. None of those are strengths. The Onley Stream cipher. How would you know his ***?
04:38
So if you were to see something I blowfish past two fish walk, walk, walk, walk, block The only one that I need you to know for straight.

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