What is symmetric encryption?

Encryption is the process of transforming readable plain text into unreadable ciphertext to mask sensitive data from unauthorized users. According to the IBM Cost of a Data Breach Report, organizations that use encryption can reduce the financial impact of a data breach by over USD 200,000.

Almost everything people do on their computers, phones and IoT devices relies on encryption to protect data and secure communications. It can protect data at rest, in transit and while being processed, making it critical to almost every organization’s cybersecurity posture.

Symmetric encryption, also known as symmetric key cryptography or secret-key encryption, is one of 2 main methods of encryption alongside asymmetric encryption. Symmetric encryption works by creating a single shared key to encrypt and decrypt sensitive data. The main advantage of symmetric encryption is that it’s simple and efficient in securing data.

However, symmetric encryption is often considered less secure than asymmetric encryption, largely because it relies on secure key exchange and meticulous key management. Anyone who intercepts or obtains the symmetric key can access the data.

For this reason, organizations and messaging apps increasingly rely on a hybrid encryption method that uses asymmetric encryption for secure key distribution and symmetric encryption for subsequent data exchanges.

Also, as advancements in artificial intelligence (AI) and quantum computing threaten to undo traditional encryption methods, many organizations are relying on integrated encryption solutions to protect sensitive data.

The two types of encryption have distinct characteristics and use cases. Asymmetric encryption uses two keys—a public key and a private key—to encrypt and decrypt data, whereas symmetric encryption uses one.

Having two different keys generally makes asymmetric encryption (also known as public key cryptography and public key encryption) more secure and versatile.

Asymmetric key cryptography can facilitate the creation of digital signatures and ensure core information security principles such as integrity, authentication and nonrepudiation. Integrity confirms that unauthorized parties do not tamper with data, authentication verifies the data origins and nonrepudiation prevents users from denying legitimate activity.

However, the downside of asymmetric encryption is that it often requires more processing power to operate, making it relatively infeasible for large amounts of data.

For this reason, organizations generally choose symmetric encryption when efficiency is critical, such as encrypting large volumes of data or securing internal communications within a closed system. They choose asymmetric encryption when security is paramount, such as encrypting sensitive data or securing communication within an open system.

Symmetric encryption starts with key generation, which creates a single secret key that all parties involved must keep confidential.

During the encryption process, the system feeds plain text (original data) and the secret key into a data encryption algorithm. This process uses mathematical operations to transform the plain text into ciphertext (encrypted data). Without a decryption key, deciphering encrypted messages becomes impossible.

The system then transmits the ciphertext to the recipient, who uses the same secret key to decrypt the ciphertext back into plain text, reversing the encryption process.

Symmetric encryption involves two main types of symmetric ciphers: block ciphers and stream ciphers.

• Block ciphers, such as the Advanced Encryption Standard (AES), encrypt data in fixed-size blocks.
  
  
• Stream ciphers, like RC4, encrypt data one bit or byte at a time, making them suitable for real-time data processing.

Users frequently choose block ciphers to ensure data integrity and security for large amounts of data. They choose stream ciphers to encrypt smaller, continuous data streams efficiently, such as real-time communications.

Organizations are increasingly combining symmetric and asymmetric encryption for security and efficiency. This hybrid process begins with a secure key exchange, where asymmetric encryption is used to securely exchange the symmetric key.

For example, web browsers and web servers establish secure communications through an SSL/TLS handshake. This process involves generating a shared symmetric key, called a session key that uses the server's public key to encrypt and share that session key between both parties.

A trusted third party, known as a certificate authority (CA), confirms the validity of the server's public key and issues a digital certificate, ensuring the server's authenticity and preventing man-in-the-middle attacks.

Once shared, the symmetric key efficiently handles all data encryption and decryption. For instance, a live video streaming service might use asymmetric encryption to secure the key exchange and symmetric stream ciphers for real-time data encryption. This efficient use of the symmetric key is a crucial advantage of this combined encryption approach.

Two common methods used in secure key exchange are Diffie-Hellman and Rivest-Shamir-Adleman (RSA). Diffie-Hellman is an asymmetric algorithm named after its inventors. Both help establish a secure key exchange and ensure that the symmetric key remains confidential.

• Diffie-Hellman allows two parties to generate a shared secret—like a symmetric key—over an insecure channel without having prior shared secrets. This method ensures that even if an attacker intercepts the exchange, they cannot decipher the shared secret without solving a complex mathematical problem.
  
  
• Alternatively, RSA uses a public and private key pair. The sender encrypts the symmetric key with the recipient's public key, which only the recipient can decrypt by using their private key. This method ensures that only the intended recipient can access the symmetric key.

Imagine Alice wants to send a confidential document to Bob. In this scenario, symmetric encryption would work as follows:

1. Alice and Bob agree on a secret key or use asymmetric encryption for secure key exchange.
2. Alice encrypts the document by using the secret key, turning it into unreadable ciphertext.
3. Alice sends the ciphertext to Bob.
4. Upon receiving the encrypted document, Bob uses the same secret key to decrypt it back to its original form, ensuring its confidentiality throughout transmission.
   

Encryption key management is the process of generating, exchanging and managing cryptographic keys to ensure the security of encrypted data.

Effective key management is crucial for all encryption methods. However, it is especially critical for symmetric encryption, which many experts see as less secure due to its single shared key and the need for secure key exchange.

If the encryption process functions as a safe for sensitive information, then an encryption key is the lock code required to open the safe. If that code falls into the wrong hands or gets intercepted, you risk losing access to your valuables or losing them to theft. Similarly, organizations that don’t properly manage their cryptographic keys can lose access to their encrypted data or expose themselves to data breaches.

For example, Microsoft recently disclosed that a China-backed hacking group stole a critical cryptographic key from its systems.¹ This key allowed hackers to generate legitimate authentication tokens and access cloud-based Outlook email systems for 25 organizations, including multiple US government agencies.

To protect against attacks like these, organizations often invest in key management systems. These services are critical given that organizations frequently manage a complex network of cryptographic keys, and many threat actors know where to look for them.

Encryption key management solutions often include features like:

• A centralized management console for encryption and encryption key policies and configurations

• Encryption at the file, database and application levels for on-premises and cloud data

• Role- and group-based access controls and audit logging to help address compliance

• Automated key lifecycle processes

• Integration with the latest technologies, such as AI, to improve key management by using analytics and automation

Organizations are increasingly using AI systems to help automate key management processes, including key generation, distribution and rotation.

For instance, AI-driven key management solutions can dynamically generate and distribute encryption keys based on real-time data usage patterns and threat assessments.

By automating key management processes, AI can significantly reduce the risk of human error and ensure that encryption keys are regularly updated and secure. Automated key rotation also makes it harder for threat actors to use keys they manage to steal.

Symmetric encryption is critical for modern data security practices. Its efficiency and simplicity often make it a preferred choice for various applications. Common symmetric encryption uses include:

• Data security (particularly for large amounts of data)

• Secure communication and web browsing

• Cloud security

• Database encryption

• Data integrity

• File, folder and disk encryption

• Hardware-based encryption

• Compliance management

Symmetric encryption is among the most critical and widespread data security tools. In fact, a recent report by TechTarget found that the primary contributor to data loss was a lack of encryption. ²

By encoding plain text as ciphertext, encryption can help organizations protect data against a range of cyberattacks, including ransomware and other malware.

Notably, the use of infostealer malware that exfiltrates sensitive data is up, according to the IBM X-Force Threat Intelligence Index. Encryption helps combat this threat by making data unusable to hackers, defeating the purpose of stealing it.

Symmetric encryption is effective for encrypting large amounts of data because it’s computationally efficient and can process high volumes of data quickly.

Organizations extensively use symmetric encryption to secure communication channels. Protocols like Transport Layer Security (TLS) use symmetric encryption to efficiently protect the integrity and confidentiality of data transmitted over the internet, including emails, instant messaging and web browsing.

During an SSL/TLS handshake, the client obtains the website's public key from its SSL/TSL certificate to establish a secure session key while the website keeps its private key secret.

The initial handshake uses asymmetric encryption to exchange information and establish a secure session key before transitioning to symmetric encryption for more efficient data transmission. This combination ensures that sensitive data remains private and tamper-proof during transmission.

While cloud service providers (CSPs) are responsible for the security of the cloud, customers are responsible for security in the cloud, including the security of any data.

Enterprise-wide data encryption can help organizations protect their sensitive data on-premises and in the cloud, ensuring that stolen data remains inaccessible without the encryption key even if a data breach occurs.

Recent research indicates that today, most organizations employ a hybrid cryptographic infrastructure through both cloud-based and on-premises cryptographic solutions.²

Databases often store vast amounts of sensitive information, from personal details to financial records. Symmetric encryption can help encrypt these databases or specific fields within them, such as credit card and social security numbers.

By encrypting data at rest, organizations can ensure that sensitive data remains protected even if the database is compromised.

Symmetric encryption algorithms not only ensure confidentiality but also data integrity, a critical factor in financial transactions. By generating message authentication codes (MACs), symmetric keys can help confirm that no one altered the data during transmission.

Hash functions also play a significant role in verifying data integrity. Hash functions generate a fixed-size hash value from input data. These "digital fingerprints" can be compared before and after transmission. If the hash has changed, that means someone has tampered with it.

Organizations often use symmetric encryption to secure files stored on local systems, shared drives and removable media.

Encrypting files ensures that sensitive data remains confidential, even if the storage media is lost or stolen. Whole disk encryption extends this protection by encrypting entire storage devices, safeguarding sensitive data on endpoints such as laptops and mobile devices.

For more protection of sensitive data, especially when software-based encryption might not suffice, organizations often use specialized hardware components like encryption chips or modules. These hardware-based encryption solutions are commonly found in smartphones, laptops and storage devices.

Many industries and jurisdictions have regulatory requirements mandating that organizations use certain kinds of encryption to protect sensitive data. Compliance with these regulations helps organizations avoid legal penalties and maintain customer trust.

The Federal Information Processing Standards (FIPS) are a set of standards developed by the National Institute of Standards and Technology (NIST) for computer systems used by nonmilitary US government agencies and contractors. They focus on ensuring the security and interoperability of data and cryptographic processes.

The most well-known symmetric key algorithms include:

• Data Encryption Standard (DES) and Triple DES (3DES)

• Advanced Encryption Standard (AES)
  

• Twofish

• Blowfish

IBM first introduced DES in the 1970s as the standard encryption algorithm, a role it held for many years. However, its relatively short key length (56 bits) made it vulnerable to brute-force attacks, where threat actors try different keys until one works.

Triple DES, developed as an enhancement, applies the DES algorithm three times to each data block, significantly increasing the key size and overall security.

Eventually, more secure symmetric algorithms replaced both DES and Triple DES.

AES is considered the gold standard of symmetric encryption algorithms. It is commonly used by organizations and governments worldwide, including the US government. AES offers strong security with key lengths of 128, 192 or 256 bits. Longer key lengths are more resistant to cracking.

AES-256, which uses a 256-bit key, is known for its high level of security and is often used in highly sensitive situations. AES is also highly efficient in both software and hardware implementations, making it suitable for a wide range of applications.

Twofish is a symmetric key block cipher known for its speed and security. It operates on blocks of data with a block size of 128 bits and supports key lengths of 128, 192 or 256 bits.

Twofish is open source and resistant to cryptanalysis, making it a reliable choice for secure applications. Its flexibility and performance suit software and hardware implementations, particularly where security and performance are critical.

Blowfish is a symmetric key block cipher designed to provide a good encryption rate in software and secure data encryption. It supports key lengths from 32 bits to 448 bits, making it flexible and suitable for various applications.

Blowfish is known for its speed and effectiveness and is popular for software encryption. It's also popular in applications that need a simple and fast encryption algorithm, although newer algorithms like Twofish and AES have largely replaced it for most use cases.