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In the realm of information security, the need to protect sensitive data from unauthorized access has led to the development of various encryption methods. One such method is symmetric key encryption, which uses a single key for both encryption and decryption. This approach is fast, efficient, and relatively easy to implement, making it a popular choice for securing communication and data storage.

Symmetric key algorithms or symmetric cryptography encryption, symmetric ciphers are encryption methods in which the same cryptographic key is used for encryption and decryption. Before the invention of asymmetric ciphers, the only method that existed was symmetric encryption. The algorithm key must be kept secret by both parties, measures must be taken to protect access to the channel, along the entire path of the cryptogram, or by the parties of interaction through crypto objects and messages, if this interaction channel is marked “Not for use by third parties”. The encryption algorithm is chosen by the parties before the exchange of messages.

Data encryption algorithms are widely used in computer systems for hiding confidential and commercial information from malicious use by third parties. The main principle in them is the condition that the transmitter and receiver know in advance the encryption algorithm, as well as the key to the message, without which the information is just a set of characters that do not make sense.

Encryption provides three states of information security:

- Encryption is used to hide information from unauthorized users during transmission or storage.
- Encryption is used to prevent information from being changed during transmission or storage.
- Encryption is used to authenticate the source of the information and prevent the sender of the information from denying that the data was sent to them.

Almost all communication in modern messengers is based on symmetric key protocols. All our bank payments, transfers, and online payments are also transferred as encrypted data using a symmetrical method. Symmetric encryption in banking is used for example to protect all payment cards PIN codes to transfer to the bank when you enter them on a PoS terminal or an ATM. Any secure communication line, from the government to the private, uses symmetric encryption.

Most symmetric ciphers use a complex combination of a large number of substitutions and permutations. Many such ciphers are executed in several (sometimes up to 80) passes, using a “pass key” on each pass. The set of “pass keys” for all passes is called the “key schedule”. As a rule, it is created from the key by performing certain operations on it, including permutations and substitutions.

A typical way to construct symmetric algorithms is the Feistel network. The algorithm builds an encryption scheme based on the function F(D, K), where D is a piece of data half the size of the encryption block, and K is the “pass key” for this pass. The function is not required to be invertible – its inverse function may not be known. The advantages of the Feistel network are the almost complete coincidence of decryption with encryption (the only difference is the reverse order of the “pass keys” in the schedule), which greatly simplifies the hardware implementation.

Often, the strength of the symmetric key encryption algorithms, especially against differential cryptanalysis, depends on the choice of values in substitution tables (S-boxes). At a minimum, it is considered undesirable to have fixed elements S(x) = x, as well as the absence of the influence of some bit of the input byte on some bit of the result – that is, cases when the result bit is the same for all pairs of input words that differ only in this bit.

The classic examples of symmetric key cryptography algorithms are listed below:

Block ciphers:

- AES Advanced Encryption Standard – American encryption standard
- DES Data Encryption Standard – US Data Encryption Standard
- 3DES Triple-DES
- RC2 Rivest Cipher, Rivest Cipher, or Ron’s Cipher
- RC5
- blowfish
- Twofish
- NUSH
- IDEA International Data Encryption Algorithm
- CAST by the initials of developers Carlisle Adams and Stafford Tavares
- CRAB
- 3-WAY
- Khufu and Khafre

Stream ciphers:

- RC4 variable length encryption algorithm
- SEAL Software Efficient Algorithm
- WAKE World Auto Key Encryption algorithm

Keeping the key secret is an important task for establishing and maintaining a secure communication channel. In this regard, there is a challenge when it comes to initial key transfer – key synchronization. If the key is transmitted over an open communication channel, it can be spied on. In addition, there are methods of crypto attacks that allow decrypting information without a key or by intercepting it at the negotiation stage.

In general, these points are dependent on the cryptographic strength of a particular encryption algorithm and are worth considering when choosing a specific algorithm. To organize a closed communication channel, you need an encryption key, which also needs to be transmitted securely. This problem can be solved with help of asymmetric encryption. For example, you can use Diffie-Hellman key exchange algorithm as a part of your system for symmetric cipher session keys transfer.

Key management plays a critical role in cryptography as the basis for ensuring the confidentiality of information exchange, identification, and data integrity. An important feature of a well-designed key management system is the reduction of complex security problems of multiple keys, which can be solved by providing their physical isolation in dedicated rooms and tamper-proof equipment like certified HSMs (Hardware Security Module). Key management should be established through the whole encryption key lifecycle: from key generation to its destruction.

The key information must be changed before the key expires. For this, valid key information, key distribution protocols, and key levels can be used. To limit the damage from key compromise, dependencies between valid and established key information should be avoided.

As a rule, in telecommunication applications, keys with a short validity period are used. Keep in mind that the term “short lifetime” refers only to the lifetime of the key, not the length of time the key must remain secret.

In symmetric key management systems, there is a problem with identifying cryptographic keys and additional information about them. An example of such information can be key release timestamps, their validity period, as well as access parameters, and key usage rules. This problem is addressed in many key management solutions, but it is worth paying special attention to this issue to prevent potential security problems if the system does not have such capabilities.

Key management is usually done in the context of a specific security policy. The security policy directly or indirectly defines the threats that the system must counter. For symmetric keys, the most important threats to pay attention to are the compromise of the confidentiality of secret keys and the unauthorized use of such keys. The latest threat also involves the use of expired keys.

A reciprocal cipher is a cipher in which the plaintext is put into a cryptographic system to produce the ciphertext. In this case, if you enter the ciphertext in the same place of the cryptographic system, the plaintext will be obtained at its output. A reciprocal cipher is also sometimes called a self-reciprocal cipher.

Almost all mechanical cipher machines are implementations of reciprocal ciphers, a mathematical involution for each letter entered. Instead of developing two types of machines, one for encryption and one for decryption, all machines can be identified and can be configured in the same way.

Symmetric key cryptography is ideal for encrypting information “for yourself”, for example, to prevent unauthorized access to it in the absence of the owner. This can be either archival encryption of selected files or transparent (automatic) encryption of entire logical or physical drives.

Possessing a high speed of encryption process, single encryption key cryptosystems allow for solving many important problems of information protection. However, the autonomous use of symmetric cryptosystems in computer networks raises the problem of distributing encryption keys between users.

The strength of a cryptographic algorithm is determined by the length of the key. Currently, for modern block symmetric encryption models, a key length of 128 bits is considered sufficient, while asymmetric encryption systems use keys of at least 1024 bits, and elliptic curve cryptography uses 256-bit keys.

Symmetric key encryption remains a critical tool in safeguarding sensitive data, providing a fast and efficient means of encoding and decoding information. With its widespread use in various industries, it is clear that this encryption method will continue to play a significant role in information security. At this point, Helenix has been distributing cryptographic solutions for a wide variety of organizational needs for over 10 years, to find out more, check out our Custom Development section.

Symmetric encryption is a technique where a single key is used to both encrypt and decrypt data. This key is shared between the sender and recipient, making it a faster and more efficient method of encryption.

Symmetric encryption uses a single shared key, while asymmetric encryption uses two separate keys – a public key for encrypting data and a private key for decrypting it. Asymmetric encryption provides more security but can be slower.

Symmetric encryption is commonly used to secure data in transit over a network, such as in HTTPS connections for secure browsing. It is also used in encrypting files on a hard drive, as well as in encrypting email messages.

TLS, or Transport Layer Security, uses both symmetric and asymmetric encryption. Symmetric encryption is used for bulk data encryption, while asymmetric encryption is used for key exchange and digital signatures.

AES cipher or Advanced Encryption Standard cipher, is a symmetric encryption algorithm. It uses a single key for both encryption and decryption of data, making it faster and more efficient for securing large amounts of data.