Secret Key Cryptography, also known as symmetric key cryptography, is a type of encryption where a single secret key is used for both encryption and decryption of a message. The cryptographic key is kept secret between the sender and receiver, making it difficult for anyone else to decipher the message. This type of cryptography is commonly used in situations where secure communication is necessary, such as in financial transactions and military communication.
Cryptography is the science of methods for ensuring confidentiality, data security, authentication, and encryption. This is one of the oldest sciences, its history goes back several thousand years.
Initially, cryptography studied methods of information encryption – the reversible transformation of plaintext based on a secret algorithm or key into ciphertext. Traditional cryptography forms a branch of symmetric cryptosystems in which encryption and decryption are performed using the same secret key.
In addition to this section, modern cryptography includes asymmetric cryptosystems, digital signature systems, hash functions, key management, obtaining hidden information, and quantum cryptography.
Cryptography is not a protection against fraud, bribery, or blackmail of legitimate subscribers, theft of keys, and other threats to information that occur in secure data transmission systems.
Secret key cryptography or symmetric cryptography is an encryption method in which the same cryptographic key is used for both encryption and decryption. Before the invention of the asymmetric encryption scheme with a public key mechanism, the only cryptographic method that existed was symmetric encryption.
The secret key is like the lock key that can both close and open the lock. Obviously, the key of the algorithm must be kept secret by both parties, measures must be taken to protect access to the channel, along the entire path of the cryptogram.
Cryptographic algorithms are widely used in computer technology 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.
The complete loss of all statistical regularities of the original message is an important requirement for a symmetric cipher. To do this, the cipher must have an “avalanche effect” – there must be a strong change in the cipher block with a 1-bit change in the input data.
Also, an important requirement is the absence of linearity: the conditions f(a) xor f(b) == f(a xor b)). Otherwise, it is easier to apply differential cryptanalysis to the cipher.
The classic examples of secret key cryptography are the algorithms listed below:
Secret key cryptography is used for data exchange in many modern services, often in combination with public key cryptography. It is also used in authentication protocols like Kerberos to authenticate parties and to prove their identity to one another in a secure manner over a non-secure network.
For example, messengers protect correspondence using such ciphers. The key for symmetric encryption is usually delivered in an asymmetrically encrypted form, while video communication services are usually delivered as audio and video streams. In the secure transport protocol TLS, symmetric encryption is used to ensure the confidentiality of transmitted data.
At the same time, secret key cryptography algorithms cannot be used to generate digital signatures and certificates, because the secret key when using this method must be known to everyone who works with the cipher. This contradicts the very idea of an electronic signature: the possibility of verifying its authenticity without contacting the owner.
A public key cryptographic system or asymmetric encryption is an encryption or digital signature system in which the public key is transmitted over an open, unsecured, observable channel and is used to verify the digital signature and encrypt the message.
The advantages in comparison with public key cryptography include the following features of secret key cryptography:
In turn, the disadvantages of cryptography with a secret key include:
An important disadvantage of secret key cryptography is the impossibility of using them in the mechanisms for generating electronic digital signatures and certificates since the key is known to each party.
To compensate for the shortcomings of symmetric cryptographic protocols, a combined (hybrid) cryptographic scheme is currently widely used, where a session key is transmitted using asymmetric encryption, which is used by parties to exchange data using secret key encryption.
Quantum computing and quantum cryptography are now only on their way to mass adoption. However, it is already possible to conclude how this may affect cryptography soon.
Most secret key cryptography ciphers are supposedly resistant to attacks by quantum computers, which in theory pose a threat to asymmetric algorithms.
Quantum cryptography is a cybersecurity method based on the principles of quantum physics. Unlike traditional cryptography, which uses mathematical methods to secure information, quantum cryptography is focused on physics, considering cases where information is carried by quantum mechanics. The process of sending and receiving information is always carried out by physical means, for example, using electrons in an electric current, or photons in fiber optic communication lines.
Using quantum phenomena, it is possible to design and build a communication system that can always detect eavesdropping. This is ensured by the fact that an attempt to measure interrelated parameters in a quantum system introduces changes to it, destroying the original signals, which means that legitimate users can recognize the degree of interceptor activity by the noise level in the channel.
A secret key is a shared piece of information used in cryptography to encrypt and decrypt data. It is a single key that is known only to the sender and receiver of the encrypted message.
A secret key is used in symmetric-key cryptography, where a single key is used for encryption and decryption algorithms. A private key is used in asymmetric-key cryptography, where there are two different keys for encryption and decryption.
The two main cryptographic functions of secret key cryptography are confidentiality and integrity. Confidentiality ensures that the message is protected from unauthorized access while in transit, and integrity ensures that the message has not been altered or tampered with during transmission.