-: Previously, we spoke about the symmetric
algorithms and how to use a share secret
or private key to conduct the encryption
and decryption functions.
In this lesson, we're going to cover a little
bit of detail about the common symmetric algorithms
that you have to know for this security class exam.
This includes DES, triple DES, IDEA, AES,
Blowfish, Twofish, and the Rivest Ciphers,
RC four, RC five, and RC six.
The Data Encryption Standard or DES
uses a 64-bit key with eight bits of that
being used for parity.
Therefore, DES only really has an effective
key length of 56-bits,
which is you probably guess by now,
mean it's not very secured against
modern computing power.
DES was heavily used in the 1970s and used
all the way up until the early 2000s.
With DES, each messages broke it up in this 64-bit blocks
and put through 16 rounds of transposition
and substitution to create the cipher text.
Due to DES weakness and its key, a modified
version of it known as Tripe DES,
written as three DES was also created.
And in this version, there was three 56-bit keys used.
The input data will subjected to encryption
through the DES algorithm with the first key
then decrypted through the algorithm
using the second key.
Again, this jumbles it up even more
and then puts it through the DES algorithm
again through another encryption function
using that third key.
This effectively created an algorithm
that had a 112-bit key
but it was three times slower than DES
because of all those encrypting, decrypting
and encrypting functions.
Our next symmetric algorithm is called IDEA.
IDEA stands for the International Data
Encryption Algorithm and it's another symmetric
block cipher which used a 64-bit block
as its input and it uses that encrypt the data.
The key size here is 128-bits and it's faster
and harder to break than DES
but it's not as widely used as the more
common one AES which we're going to talk
about in a moment.
IDEA is commonly known only because
it's really used inside a pretty good
privacy suite which we'll talk about
a little bit later on in the future lesson.
Ultimately, DES and triple DES simply
weren't strong enough though and there
was this contest held to design a replacement.
IDEA was one entrance to the contest but ultimately,
it didn't win.
The one that won is known as AES
which is the Advanced Encryption Standard.
AES was chosen as the replacement for DES
and triple DES by the US government.
AES can be used with a 128-bit,
192-bit or 356-bit key and a matching block size.
AES is known as the Rijndael algorithm as well
which is named after its creator
but most people simply called it AES.
AES is widely used and it has become
the de facto standard in encryption.
In fact, it's still encryption standard
that's used by the federal government
for any encryption of sensitive
but unclassified information.
Next, we have Blowfish which is a block
cipher that uses a 32-bit to 448-bit encryption key
to encrypt 64-bit of data in blocks at a time.
It was originally developed as replacement for DES
but wasn't widely utilized.
Another variant called Twofish was also developed
and this one provides the ability to use
128-bit blocks in its encryption algorithm
and use 128-bit, 192-bit, or 256-bit encryption keys.
Both Blowfish and Twofish were never patterned then
and they were available for use as open source.
Another set of symmetric algorithms was created
by Ron Rivest, a cryptographer who's created
six algorithms under the name RC
which stands for the Rivest Cipher.
RC one was never published.
RC two was considered weak eventually
and skipped over.
And RC three was cracked before it was
even released to the public.
But RC four, RC five and RC six were released
and can be found in common use today.
RC four is a stream cipher
and it uses a variable key size from 40-bits
all the way up to 2048-bits.
RC four is used in both Secure Sockets Layer, SSL
and Wired Equivalent Privacy, WEP.
Now, RC five is a block cipher,
using key sizes up to 2048-bits.
And RC six is based on the RC five cipher
and it was really originally considered
as the replacement for DES until Rijndael
cipher was chosen as the winner
and became the Advanced Encryption Standard or AES.
Now, for the exam, if you're asked about
these algorithms, you should be able to identify
which of these are block ciphers
and which are stream ciphers.
Here's the hint,
the only stream cipher we've talked about
so far is RC four.
All of the others are block ciphers.
If you're not sure in the exam,
choose block cipher because it is
most commonly used and most commonly
asked on the exam.
Also, you should be able to identify
the algorithm as either symmetric ciphers
or asymmetric ciphers.
Everything I've just covered in this lesson
including DES, triple DES, IDEA, AES,
Blowfish, Twofish, and the Rivest Ciphers
are all considered symmetric ciphers.
Keep this in mind when you take them exam
and you're going to do great.
(electronic music)