Understanding Cryptography Algorithms

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If you’re planning to take the SY0-501 version of the Security+ exam, you should have a good understanding of cryptography algorithms and their basic characteristics. This includes symmetric algorithms like AES, DES, 3DES, RC4, Blowfish/Twofish.

For example, can you answer this question?

Q. An application developer needs to use an encryption protocol to encrypt credit card data within a database used by the application. Which of the following would be the FASTEST, while also providing strong confidentiality?

A. AES-256

B. DES

C. Blowfish

D. SHA-2

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation are available at the end of this post.

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Symmetric encryption uses the same key to encrypt and decrypt data. For example, when transmitting encrypted data, symmetric encryption algorithms use the same key to encrypt and decrypt data at both ends of the transmission media.

AES

The Advanced Encryption Standard (AES) is a strong symmetric block cipher that encrypts data in 128-bit blocks. The National Institute of Standards and Technology (NIST) adopted AES from the Rijndael encryption algorithm after a lengthy evaluation of several different algorithms. NIST is a U.S. agency that develops and promotes standards. They spent about five years conducting a review of 15 different symmetric algorithms and identified AES as the best of the 15.

AES can use key sizes of 128 bits, 192 bits, or 256 bits, and it’s sometimes referred to as AES-128, AES-192, or AES-256 to identify how many bits are used in the key. When more bits are used, it makes it more difficult to discover the key and decrypt the data. AES-128 provides strong protection, but AES-256 provides stronger protection.

In general, the size of the key for any encryption directly corresponds to the key strength.

Longer keys for a specific algorithm result in stronger key strength.
Because of its strengths, AES has been adopted in a wide assortment of applications. For example, many applications that encrypt data on USB drives use AES. Some of the strengths of AES are:

• Fast. AES uses elegant mathematical formulas and only requires one pass to encrypt and decrypt data. In contrast, 3DES (mentioned later in this chapter) requires multiple passes to encrypt and decrypt data.

• Efficient. AES is less resource intensive than other encryption algorithms such as 3DES. AES encrypts and decrypts quickly even when ciphering data on small devices, such as USB flash drives.

• Strong. AES provides strong encryption of data, providing a high level of confidentiality.

DES

Data Encryption Standard (DES) is a symmetric block cipher that was widely used for many years, dating back to the 1970s. It encrypts data in 64-bit blocks. However, it uses a relatively small key of only 56 bits and can be broken with brute force attacks. In the ’70s, the technology required to break 56-bit encryption wasn’t easily available, but with the advances in computer technology, a 56-bit key is now considered trivial. DES is not recommended for use today.

3DES

3DES (pronounced as “Triple DES”) is a symmetric block cipher designed as an improvement over the known weaknesses of DES. In basic terms, it encrypts data using the DES algorithm in three separate passes and uses multiple keys. Just as DES encrypts data in 64-bit blocks, 3DES also encrypts data in 64-bit blocks.

Although 3DES is a strong algorithm, it isn’t used as often as AES today. AES is much less resource intensive. However, if hardware doesn’t support AES, 3DES is a suitable alternative. 3DES uses key sizes of 56 bits, 112 bits, or 168 bits.

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RC4

Ron Rivest invented several versions of RC, which are sometimes referred to as Ron’s Code or Rivest Cipher. The most commonly used version is RC4 (also called ARC4), which is a symmetric stream cipher and it can use between 40 and 2,048 bits.

RC4 has enjoyed a long life as a strong cipher. For many years, it has been the recommended encryption mechanism in SSL and TLS, when encrypting HTTPS connections on the Internet.

However, experts have speculated since 2013 that agencies such as the U.S. National Security Agency (NSA) can break RC4, even when implemented correctly such as in TLS. Because of this, companies such as Microsoft recommend disabling RC4 and using AES instead. Even though AES is a block cipher and RC4 is a stream cipher, TLS can implement either one.

Blowfish and Twofish

Blowfish is a strong symmetric block cipher that is still widely used today. It encrypts data in 64-bit blocks and supports key sizes between 32 and 448 bits. Bruce Schneier (a widely respected voice in IT security) designed Blowfish as a general-purpose algorithm to replace DES.

Interestingly, Blowfish is actually faster than AES in some instances. This is especially true when comparing Blowfish with AES-256. Part of the reason is that Blowfish encrypts data in smaller 64-bit blocks, whereas AES encrypts data in 128-bit blocks.

Twofish is related to Blowfish, but it encrypts data in 128-bit blocks and it supports 128-, 192-, or 256-bit keys. It was one of the finalist algorithms evaluated by NIST for AES. However, NIST selected Rijndael as AES instead.

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Symmetric Encryption Summary

The table summarizes the important symmetric algorithms and their basic characteristics. The items marked with an asterisk (RC4 and DES) are no longer recommended for use, but are still included in the CompTIA Security+ objectives.

Understanding Cryptography AlgorithmsSymmetric encryption protocols

If you can recognize the symmetric algorithms such as AES, DES, 3DES, Blowfish, and Twofish, it will help you answer many exam questions. For example, if a question asks what you would use to hash data and it lists encryption algorithms, you can quickly eliminate them because encryption algorithms don’t hash data. You should also know the size of the blocks and the size of the keys listed in the table.


Q. An application developer needs to use an encryption protocol to encrypt credit card data within a database used by the application. Which of the following would be the FASTEST, while also providing strong confidentiality?

A. AES-256

B. DES

C. Blowfish

D. SHA-2

Answer is C.  Blowfish would be the fastest in this scenario. Blowfish provides strong encryption, so   it would provide strong confidentiality.

Advanced Encryption Standard-256 (AES-256) is a strong encryption protocol, but Blowfish is faster than AES in some situations, such as when comparing it against AES-256.

Data Encryption Standard (DES) is not secure and is not recommended today.

Secure Hash Algorithm version 2 (SHA-2) is a hashing algorithm used for integrity.

See Chapter 10 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide for more information on encryption.

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