Symmetric Encryption Explained in 5 Minutes or Less

Symmetric encryption is a fast and secure type of encryption that uses a single key for encryption and decryption.

Encryption is the process of converting human-readable information into a scrambled, unreadable format called ciphertext. This is done to prevent access to sensitive information by unauthorized people.

To encrypt data, random strings of bits are used by encryption algorithms to scramble the data into a form that cannot be understood. The random strings of bits used to encrypt data are called encryption keys.

In February 2009, Dave Crouse noticed suspicious transactions in his bank account. First, small transactions of less than $40 arose suspicion but didn’t alarm him. However, six months down the line, things got terrible. The transactions grew to $500, $600, and at times a total of between $2800 and $3200 in a single day.

In under six months, Crouse lost $900,000 to malicious attackers and an additional $100,00 trying to sort the mess he had gotten into.

Worse still, his social security number, address, and phone number kept being used to open bank accounts. All this was because his personal data was stolen through malware that infected his computer.

Crouse’s case is not unique. Many people and organizations have suffered costly data breaches that have not only led to the loss of critical data and disruption of service but also immense financial losses.

It is, therefore, important to ensure that sensitive information is protected from malicious attackers. An excellent way to do this is through symmetric encryption.

Symmetric Encryption

Encryption ensures that even when sensitive information falls into the wrong hands, it cannot be understood by unauthorized personnel. There are two types of encryption: asymmetric and symmetric encryption.

The difference between these two lies in the keys used for encryption and decryption. In asymmetric encryption, also known as public key encryption, there are two keys, one used for encryption and the other used for decryption. 

In symmetric encryption, one key is used to encrypt and decrypt the encrypted data. When two parties are communicating and using symmetric encryption to encrypt their data, they will both use the same key for encryption and decryption. This is why symmetric encryption is also known as shared key encryption.

Anyone with the key can encrypt the data or decrypt it back to its original form. Therefore, it is important that this key is kept secret from unauthorized people. This is also the reason why symmetric encryption is also referred to as secret key encryption. The security of symmetric encryption lies in the key remaining secret.

How Symmetric Encryption Works

There are two modes of symmetric encryption. These are stream and block modes. In stream mode, each bit of data is independently encrypted and transmitted as a continuous stream. In block mode, data to be encrypted is first divided into blocks of 56, 128, 192, or 256 bits. These blocks are then encrypted and transmitted.

When two parties use symmetric encryption, a symmetric key is generated using a symmetric encryption algorithm such as Advanced Encryption Standard (AES). This key is then shared between the parties communicating.

This can be done through a key agreement protocol such as the Elliptic Curve Diffie-Hellman Ephemeral (ECDH) or a Key Encapsulation Mechanism where a symmetric key is encrypted by a provided public key and transmitted.

Another way to share a symmetric key is through alternative communication mediums such as postal emails, telephones, or one-on-one meetings.

Once the key has been received by authorized parties, data can now be securely transmitted. The sender first decides on their preferred encryption mode, either stream or block, and encrypts the data into unreadable ciphertext. Block mode encryption, however, is the more modern and popular choice of symmetric encryption.

The encrypted data is then transmitted to the intended receiver. Upon receiving the shared data in ciphertext, the receiver uses the agreed-upon key to convert the ciphertext back into readable format. This is called decryption.

Symmetric Encryption Algorithms

Some of the common symmetric encryption algorithms include:

#1. Data Encryption Standard (DES)

DES was developed by IBM in the early 1970s to provide a secure way of encrypting data that is both easy to use and implement.

DES breaks data into blocks bits of 64 bits and uses a 56-bit key to encrypt the data. DES is, however, seen to be less secure, and NIST withdrew it as an encryption standard.

Having been created in the 1970s when processing power was limited, a 56-bit key length was not a problem. However, modern computers can brute force a 56-bit key. This is why its use is not recommended by the National Institute of Standards and Technology(NIST).

#2. Triple Data Encryption Standard(3DES, TDES)

TDES is based on the DES. It was developed to address the main weakness of DES, which is having a short key length. TDES solves this problem by breaking data into 64-bit blocks of information and applying DES on the blocks three times. This triples the 56-bit key used by DES into a more secure 168-bit key.

Although this algorithm is still being used, NIST has disallowed its use after December 31, 2023, because of security concerns as TDES is vulnerable to brute forcing.

#3. Advanced Encryption Standard(AES)

This is the most popular symmetric algorithm used over the internet. It is more secure than other symmetric encryption algorithms. AES was developed as a replacement and a solution to DES.

AES is based on the substitution-permutation network and uses a block mode of encryption. Data is broken into blocks of 128 bits which are then encrypted one block at a time.

AES uses a key length of 128, 192, or 256 bits. AES is so secure that it is used to secure very sensitive information from military agencies, banks, hospitals, and governments.

In 2001, NIST announced AES as the new standard for US government use. AES has since become the most popular and most used symmetric algorithm.

Symmetric Encryption: Considerations

When using symmetric encryption, there are several things you need to consider. These are:

Key Management

A key weakness with symmetric encryption lies in how its key is generated, distributed to authorized parties, and stored securely. Therefore, when using symmetric encryption, you must have effective key management strategies to ensure keys are managed securely, regularly changed, and not overused.

Regulatory Compliance

The symmetric algorithm used needs to be compliant with regulations. For instance, whereas  TDES is still in use, its application after December 31, 2023, will not comply with the regulation. On the other hand, using an algorithm such as DES is a complete violation of regulations. AES is, however, compliant.

Key Length

The security of symmetric encryption is directly related to the length of the key used. Picking an encryption key with a short length can be vulnerable to brute force attacks leading to data breaches.

Type of algorithm used

Each symmetric algorithm has its strengths, weaknesses, and intended devices. When using symmetric encryption, it is important to factor in the algorithm used to ensure that it provides the highest security to the encrypted data.

By factoring in all these considerations, a user can make the right choice of algorithms and key management practices to ensure that symmetric encryption serves their security needs.

Symmetric vs. Asymmetric Encryption

The differences between the two includes:

Symmetric Encryption	Asymmetric Encryption
Uses the same key for encryption and decryption	Uses two different keys, a public key for encryption and a private key for decryption
It is fast and requires little computational resource	Much slower and resource intensive
The encryption key must be exchanged securely between parties before communication	The public key can be shared openly without compromising security
Less secure since it uses a single key for encryption and decryption	More secure as it uses two different keys for encryption and encryption
Used to transmit large amounts of data	Ideal for the transmission of small volumes of data

Both symmetric and asymmetric encryption is used in modern devices as they have instances where one is a better option than the other.

Symmetric Encryption: Benefits

The use of symmetric encryption has several advantages. This includes:

Security

Symmetric encryption is very secure. For instance, when implementing the NIST-recommended symmetric encryption algorithm AES, even with modern computers, it would take billions of years to crack the key using brute force. This means when used properly, symmetric encryption is very secure.

Speed

symmetric encryption algorithms are not computationally intensive and are easy to use. This has the benefit of making symmetric encryption very fast, making it ideal for securing large amounts of data.

Regulatory compliance

With security being an important aspect of any business, it is important to comply with existing regulations to avoid penalties and breaches. Symmetric encryption algorithms such as AES are accepted by standard bodies such as NIST, which allows organizations using symmetric encryption with AES algorithm to be compliant with security regulations.

Lower computational requirement

symmetric encryption does not require a lot of computational resources and thus can be used even with limited processing resources.

If you consider speed, security, regulatory compliance, and low processing important when choosing an encryption method, then symmetric encryption will be an excellent choice.

Symmetric Encryption: Disadvantages

A key drawback with symmetric encryption is sharing encryption keys, which must be done securely. The security of symmetric encryption is pegged on the ability of users to share the encryption key securely. Even if just a portion of the key is leaked, it is possible that attackers can reconstruct the entire key

If the encryption key falls into the wrong hands, the results can be catastrophic as malicious actors can be able to access all data that was encrypted using that key. This sets users up for more damage if their key is compromised.

Its drawbacks aside, symmetric encryption is still a good way to secure data, particularly if you want to secure it at rest.

Encryption: Learning Resources

To learn more about symmetric encryption, consider going through the following resources:

#1. Symmetric Encryption-Algorithm, Analysis, and Applications

This book which is aimed at graduate students, researchers, and practicing professionals, prescribes different symmetric encryption techniques which have a lot of relevance to the security of data and computer systems.

The book unfolds with introductory definitions that readers will encounter in symmetric encryption before covering and analyzing various symmetric encryption techniques and their usage.

The book, which features many examples that help to break down and illustrate complex concepts, is a good read for anyone interested in taking their knowledge of symmetric encryption to the next level.

#2. Symmetric Key Algorithms

This book is an excellent read for beginners interested in a stop shop to learn about various symmetric encryption algorithms in an easy-to-understand manner.

The book covers all the vocabulary used in cryptography and provides examples to augment the explanations of the concepts. It then progresses to break down the building blocks for symmetric encryption providing illustrations and concise, easy-to-understand explanations.

This book is highly recommended for readers interested in broadly learning about cryptography and encryption without taking an in-depth dive into difficult concepts in the subject.

#3. Cryptography: Learn All Encryption Algorithms

This Udemy Course is a good choice for anyone interested in learning about cryptography, particularly symmetric and asymmetric encryption. The course offers a brief introduction to encryption and familiarizes learners with all terms they may encounter while learning encryption.

It then explores the different types of attacks mounted against encrypted data and covers cryptography techniques that can be applied to prevent attacks from happening. With that covered, the instructor offers an in-depth study on ciphers and covers the different types of ciphers used for encryption.

#4. Encryption and Cryptography for Professionals

To anyone interested in dipping their feet into encryption and cryptography, this Udemy Course is the best buck for your money. The course assumes learners are completely new to cryptography and encryption, and thus, it starts with an introduction to cryptography, information theory, and the building blocks of encryption.

It then progresses to intermediate topics and covers symmetric and asymmetric encryption algorithms and hash functions and algorithms. It also includes more advanced concepts such as post-quantum cryptography, ring signatures, secure multi-party computation, and zero-knowledge proofs.

Conclusion

Symmetric encryption is very useful in securing data in transit and at rest. To protect yourself from costly data breaches, consider encryption your data using symmetric encryption, which will not interfere with the speed of the storage device or increase demand on processing power.

To learn more about symmetric encryption, consider reading the recommended books or taking the suggested courses.

You may also explore cloud cryptography, its types, and the Google Cloud deployment.