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In this lesson, we're going to discuss some

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of the different symmetric algorithms

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that you may come across when working out in the field.

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Now, a symmetric algorithm is a method

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of encryption where the same key is used

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for both encryption and decryption of your data.

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Now we're going to be covering a few

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of the most commonly used symmetric algorithms,

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including DES, 3DES, IDEA, AES, Blowfish, Twofish,

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and then Rivest Ciphers, including RC4, RC5, and RC6.

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Now first, we have DES.

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Now DES, or the Data Encryption Standard,

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is written out as DES.

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And it uses a 64-bit key,

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with eight bits of that being used for parity.

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Therefore, DES really only has an effective key length

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of 56 bits, which is, as you probably guessed by now,

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not very powerful and not very secure

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against the challenge of modern computing power.

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Now, DES was heavily used all the way back in the 1970s,

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and it was used all the way up until the early 2000s.

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With DES, each message is going to be broken up

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into 64-bit blocks,

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and then pushed through 16 rounds of transposition

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and substitution to create the final cipher text.

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Now, because of DES's weakness and its key size,

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a modified version of it known as Triple DES,

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which is written as 3DES was also created.

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Now in this version,

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we're actually going to use three different 56-bit keys.

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The input data is going to be subjected to encryption

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through the DES algorithm using the first key.

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Then the resulting cipher text will attempt

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to be decrypted using that same algorithm,

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but using the second key.

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Now, because this key doesn't actually decrypt the data,

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it just scrambles it up even further,

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and then we'll put it through the DES algorithm

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one more time using the third key

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and the encryption function.

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So we're encrypting, decrypting,

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and encrypting using three different keys,

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which really effectively creates us an algorithm

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that has 112-bit key that we're using here

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as we're going through the DES process three times,

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encrypting, decrypting, and encrypting again.

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Now, second, we have IDEA.

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Now IDEA is spelled I-D-E-A, and it stands

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for the International Data Encryption Algorithm.

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Now IDEA is another symmetric block cipher,

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and this again uses 64-bit blocks as its input,

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and then uses that to encrypt the data.

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The key size for IDEA is 128 bits,

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which makes it harder to break than DES,

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but it's not as widely utilized as the more common one

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that we're going to talk about known as AES,

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or the Advanced Encryption Standard.

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Now IDEA is commonly known only because it was really used

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a lot inside the PGP, or Pretty Good Privacy suite of tools.

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Now, ultimately, DES and 3DES that we talked about earlier

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simply were found to not be strong enough,

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and so a big contest was held

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by the National Institute of Standards and Technologies

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to create a replacement.

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IDEA was one of the entrants into this contest,

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but ultimately, they didn't win.

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The winner actually brings us to our third type,

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which is called AES, or the Advanced Encryption Standard.

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Now, the Advanced Encryption Standard

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was actually chosen as a replacement for DES and 3DES

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by the US government

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through the National Institute of Standards and Technology.

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Now, AES can be used with 128-bit key, 192-bit key,

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or a 256-bit key.

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AES is also known as the Rijndael algorithm

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or Rijndael Cipher because that was the name

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of the creator who made AES.

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But most people will simply call it AES

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because it's a lot easier to say.

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You're going to find that AES is widely used,

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and has become the defacto standard in encryption

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for symmetric key cryptography.

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In fact, it's the encryption standard

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that's being used by the federal government

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for any encryption of sensitive,

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but unclassified information.

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The fourth type we have is known as Blowfish.

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Now, Blowfish is a block cipher that uses a 32-bit

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to 448-bit encryption key and can encrypt 64 bits of data

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at a time when it's going through and doing those blocks.

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Originally, this was developed as a replacement for DES,

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but it wasn't widely utilized.

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Now the fifth one we have is another variant,

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which is known as Twofish.

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Twofish was developed to be able to provide us

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with 128-bit blocks in the encryption algorithm,

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and uses 128-bit, 192-bit, or 256-bit encryption key.

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Both Blowfish and Twofish were never patented,

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and they were released as open source products

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that people could use.

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Sixth, and finally, we have another set

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of symmetric algorithms that we need to look at

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known as the RC Cipher Suite.

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Now the RC Cipher Suite was created by Ron Rivest,

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a cryptographer who's created six algorithms

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under the name RC, which stands for Rivest Cipher.

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RC1 was never published.

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RC2 was considered weak and was skipped over.

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RC3 was actually cracked before it was even released

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to the public.

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But with RC4, RC5, and RC6,

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these were all released,

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and they're commonly used in our networks today.

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RC4 is considered to be a stream cipher,

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and it uses a variable key size from 40 bits,

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all the way up to 2,048 bits.

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RC4 is going to be used in both Secure Socket Layer, SSL,

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as well as the Wired Equivalent Privacy, or WEP,

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that's used heavily on the internet

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and on our wireless networks.

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Now, RC5 is a block cipher that uses key sizes

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up to 2,048 bits.

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And finally, we have RC6,

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which is based on the RC5 cipher,

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but is a stronger and more advanced version of it.

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And it was originally entered into the contest

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as a replacement for DES, but ultimately,

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the Rijndael Cipher, known as AES, was chosen as the winner.

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So remember, if you're being asked

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about any encryption algorithms,

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you should be able to identify it

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as a specific algorithm being symmetric or asymmetric,

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and whether it is a block or stream cipher.

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You do not need to memorize all

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of the different block sizes or key sizes.

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I just brought that up as a way for you to understand

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which ones are more or less secure than others.

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Now, as we went through this lesson,

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we talked about DES, 3DES, IDEA,

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AES, Blowfish, Twofish, RC4, RC5, and RC6.

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All these are considered to be symmetric algorithms.

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Now, most of these are also considered

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to be block ciphers except RC4.

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RC4 is the only symmetric cipher we discussed

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that is considered to be a stream cipher,

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so keep this in mind as you're working

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with the encryption out in the real world too.

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Finally, when it comes to symmetric encryption ciphers,

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the one that is most commonly used

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is going to be the Advanced Encryption Standard,

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and it's also considered to be the strongest

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of the symmetric algorithms that we covered in this lesson.