In this lesson, we're going to discuss some
of the different symmetric algorithms
that you may come across when working out in the field.
Now, a symmetric algorithm is a method
of encryption where the same key is used
for both encryption and decryption of your data.
Now we're going to be covering a few
of the most commonly used symmetric algorithms,
including DES, 3DES, IDEA, AES, Blowfish, Twofish,
and then Rivest Ciphers, including RC4, RC5, and RC6.
Now first, we have DES.
Now DES, or the Data Encryption Standard,
is written out as DES.
And it uses a 64-bit key,
with eight bits of that being used for parity.
Therefore, DES really only has an effective key length
of 56 bits, which is, as you probably guessed by now,
not very powerful and not very secure
against the challenge of modern computing power.
Now, DES was heavily used all the way back in the 1970s,
and it was used all the way up until the early 2000s.
With DES, each message is going to be broken up
into 64-bit blocks,
and then pushed through 16 rounds of transposition
and substitution to create the final cipher text.
Now, because of DES's weakness and its key size,
a modified version of it known as Triple DES,
which is written as 3DES was also created.
Now in this version,
we're actually going to use three different 56-bit keys.
The input data is going to be subjected to encryption
through the DES algorithm using the first key.
Then the resulting cipher text will attempt
to be decrypted using that same algorithm,
but using the second key.
Now, because this key doesn't actually decrypt the data,
it just scrambles it up even further,
and then we'll put it through the DES algorithm
one more time using the third key
and the encryption function.
So we're encrypting, decrypting,
and encrypting using three different keys,
which really effectively creates us an algorithm
that has 112-bit key that we're using here
as we're going through the DES process three times,
encrypting, decrypting, and encrypting again.
Now, second, we have IDEA.
Now IDEA is spelled I-D-E-A, and it stands
for the International Data Encryption Algorithm.
Now IDEA is another symmetric block cipher,
and this again uses 64-bit blocks as its input,
and then uses that to encrypt the data.
The key size for IDEA is 128 bits,
which makes it harder to break than DES,
but it's not as widely utilized as the more common one
that we're going to talk about known as AES,
or the Advanced Encryption Standard.
Now IDEA is commonly known only because it was really used
a lot inside the PGP, or Pretty Good Privacy suite of tools.
Now, ultimately, DES and 3DES that we talked about earlier
simply were found to not be strong enough,
and so a big contest was held
by the National Institute of Standards and Technologies
to create a replacement.
IDEA was one of the entrants into this contest,
but ultimately, they didn't win.
The winner actually brings us to our third type,
which is called AES, or the Advanced Encryption Standard.
Now, the Advanced Encryption Standard
was actually chosen as a replacement for DES and 3DES
by the US government
through the National Institute of Standards and Technology.
Now, AES can be used with 128-bit key, 192-bit key,
or a 256-bit key.
AES is also known as the Rijndael algorithm
or Rijndael Cipher because that was the name
of the creator who made AES.
But most people will simply call it AES
because it's a lot easier to say.
You're going to find that AES is widely used,
and has become the defacto standard in encryption
for symmetric key cryptography.
In fact, it's the encryption standard
that's being used by the federal government
for any encryption of sensitive,
but unclassified information.
The fourth type we have is known as Blowfish.
Now, Blowfish is a block cipher that uses a 32-bit
to 448-bit encryption key and can encrypt 64 bits of data
at a time when it's going through and doing those blocks.
Originally, this was developed as a replacement for DES,
but it wasn't widely utilized.
Now the fifth one we have is another variant,
which is known as Twofish.
Twofish was developed to be able to provide us
with 128-bit blocks in the encryption algorithm,
and uses 128-bit, 192-bit, or 256-bit encryption key.
Both Blowfish and Twofish were never patented,
and they were released as open source products
that people could use.
Sixth, and finally, we have another set
of symmetric algorithms that we need to look at
known as the RC Cipher Suite.
Now the RC Cipher Suite was created by Ron Rivest,
a cryptographer who's created six algorithms
under the name RC, which stands for Rivest Cipher.
RC1 was never published.
RC2 was considered weak and was skipped over.
RC3 was actually cracked before it was even released
to the public.
But with RC4, RC5, and RC6,
these were all released,
and they're commonly used in our networks today.
RC4 is considered to be a stream cipher,
and it uses a variable key size from 40 bits,
all the way up to 2,048 bits.
RC4 is going to be used in both Secure Socket Layer, SSL,
as well as the Wired Equivalent Privacy, or WEP,
that's used heavily on the internet
and on our wireless networks.
Now, RC5 is a block cipher that uses key sizes
up to 2,048 bits.
And finally, we have RC6,
which is based on the RC5 cipher,
but is a stronger and more advanced version of it.
And it was originally entered into the contest
as a replacement for DES, but ultimately,
the Rijndael Cipher, known as AES, was chosen as the winner.
So remember, if you're being asked
about any encryption algorithms,
you should be able to identify it
as a specific algorithm being symmetric or asymmetric,
and whether it is a block or stream cipher.
You do not need to memorize all
of the different block sizes or key sizes.
I just brought that up as a way for you to understand
which ones are more or less secure than others.
Now, as we went through this lesson,
we talked about DES, 3DES, IDEA,
AES, Blowfish, Twofish, RC4, RC5, and RC6.
All these are considered to be symmetric algorithms.
Now, most of these are also considered
to be block ciphers except RC4.
RC4 is the only symmetric cipher we discussed
that is considered to be a stream cipher,
so keep this in mind as you're working
with the encryption out in the real world too.
Finally, when it comes to symmetric encryption ciphers,
the one that is most commonly used
is going to be the Advanced Encryption Standard,
and it's also considered to be the strongest
of the symmetric algorithms that we covered in this lesson.