Data encryption technology - symmetric encryption and asymmetric encryption

1. Data encryption technology

        Encryption is the process of encoding data so that it appears meaningless while still maintaining its recoverable form. In this process, the transformed data is called plaintext, which can be a meaningful text or data, and the transformed data is called ciphertext. Encryption mechanisms help to protect the confidentiality and integrity of information, help to identify the source of information, and it is the most widely used security mechanism.

        Traditional encryption algorithms mainly include substitution encryption and displacement encryption. The method of substitution encryption is to first construct one or more ciphertext alphabets, and then replace the plaintext letters or letter groups with letters or letter groups in the ciphertext alphabet. The relative position of each letter or letter group remains unchanged, but itself changes; permutation encryption rearranges the letters in the plaintext, the letters themselves unchanged, but their positions changed. Traditional encryption algorithms have the characteristics of simple design and have been widely used. But one of their major weaknesses is that algorithms and keys are closely related. Attackers can relatively easily decipher ciphertext based on the statistical and linguistic knowledge of letters. Especially today with the highly developed computer technology, computers can be fully utilized for ciphertext analysis.

        Since the 1960s, with the rapid development of electronic technology and computer technology, as well as research in disciplines such as structural algebra, computability and computational complexity theory, cryptography has entered a new period of development. In the late 1970s, the emergence of symmetric encryption algorithms and asymmetric encryption algorithms became two important milestones in the history of modern cryptography.

2. Symmetric encryption

        Symmetric encryption algorithms, also known as private key encryption algorithms, mean that the encryption key and decryption key are the same, or that although they are different, the other can be easily deduced from either one. Its advantage is that it has high confidentiality strength, but the transmission of the key needs to go through a safe and reliable way. There are two basic types of symmetric encryption algorithms, block ciphers and sequence ciphers. Block ciphers operate on plaintext blocks and ciphertext blocks, and sequence ciphers perform bitwise or byte-wise operations on plaintext and ciphertext data streams.

        Symmetric encryption is an encryption technique that uses the same key for encryption and decryption. In symmetric encryption, the key used for encryption and decryption is the same, as shown in the figure below.

Basic steps of symmetric encryption :

1. Plain text data (raw data): Data that needs to be encrypted.

2. Key generation: Choose a secure key, usually 128 bits, 192 bits or 256 bits in length, etc.

3. Encryption algorithm: Taking plaintext data and key as input, ciphertext data (encrypted data) is generated through a specific encryption algorithm.

4. Ciphertext data transmission: Securely transmit ciphertext data through the network or other channels.

5. Decryption algorithm: The recipient uses the same key and the same encryption algorithm to decrypt the ciphertext data.

6. Decryption: The decryption algorithm takes ciphertext data and key as input and restores the original plaintext data.

Advantages of symmetric encryption :

• High efficiency: Symmetric encryption has fast encryption and decryption speeds and is suitable for encrypting and decrypting large amounts of data.
• Simple to implement: Symmetric encryption algorithms are generally easier to implement and deploy than asymmetric encryption algorithms.
• Wide applicability: Symmetric encryption can be used to protect the confidentiality and privacy of data.

Disadvantages of symmetric encryption :

• Key distribution and management: The sender and receiver need to share the same key in advance, and the security and confidentiality of the key are very important.
• Security limitations: The security of symmetric encryption algorithms relies on the security of the key. If the key is leaked, the confidentiality of the data may be destroyed.
• Two-party communication: Symmetric encryption is suitable for two communicating parties that trust each other, but if multi-party communication is required, key distribution and management will become more difficult.

Applicable scenarios for symmetric encryption:

1. Data transmission confidentiality : Symmetric encryption can be used to protect the confidentiality of sensitive data during network transmission. For example, when transmitting sensitive data over the Internet or an internal network, symmetric encryption ensures that only authorized users can decrypt and read the data.

2. Storage Media Encryption : Symmetric encryption can be used to protect data on storage media. For example, data on hard drives or removable storage devices can be encrypted using symmetric encryption algorithms to prevent unauthorized access and disclosure.

3. Database Encryption : Symmetric encryption can be used to encrypt sensitive data in the database. Doing so can protect the data in the database, even if the database is accessed illegally or the backup files are stolen, sensitive data will not be exposed.

4. Authentication and access control : Symmetric encryption can be used in authentication and access control scenarios. For example, during the login process, symmetric encryption algorithms can be used to encrypt and verify the credential information provided by the user to ensure that only legitimate users have access.

5. File encryption : Symmetric encryption can be used to encrypt individual files or documents. This is useful when you need to protect the confidentiality of certain files or documents on your local computer, ensuring that only authorized users are able to decrypt and access these files.

Because of its high encryption efficiency, it is suitable for encrypting information with large amounts of data.

Common algorithms for symmetric encryption :

1. DES (Data Encryption Standard): is a widely used symmetric encryption algorithm with a 56-bit key length. It has been superseded by AES, but is still used in some legacy systems.

2. 3DES (Triple Data Encryption Standard): Uses three independent DES operations to encrypt data, providing higher security. Its key length can be 56 bits or 168 bits.

3. AES (Advanced Encryption Standard): It is an advanced encryption standard that is currently widely recognized and adopted. It supports 128-bit, 192-bit, and 256-bit key lengths for increased security and performance.

4. RC4 (Rivest Cipher 4): is a stream cipher that is widely used to encrypt communications and protect data confidentiality. However, its use is now deprecated due to certain security weaknesses.

5. Blowfish : It is a fast and highly secure symmetric encryption algorithm that can be applied to various application scenarios. It supports variable length keys up to 448 bits long.

6. IDEA (International Data Encryption Algorithm): It is a block cipher algorithm, often used for encrypted communication. It uses 128-bit keys and processes data in units of 64 bits.

Extensions :

The brief process of 3DES encryption and decryption:

3DES (Triple DES): two 56-bit keys K1, K2
                                encryption: K1 encryption -> K2 decryption -> K1 encryption and
                                decryption: K1 decryption -> K2 encryption -> K1 decryption

3. Asymmetric encryption

        Asymmetric encryption (Asymmetric Encryption) is an encryption algorithm that uses two different but associated keys for encryption and decryption operations. These two keys are called public key (Public Key) and private key (Private Key).

        A public key is a secret key that can be shared publicly and used to encrypt data or verify digital signatures. The private key is kept secret, and only the owner of the key can use it to decrypt data or generate digital signatures.

        The working principle of asymmetric encryption algorithm is based on mathematical problems, such as large number decomposition, discrete logarithm, etc. These problems are considered to be computationally expensive, thus making it very difficult to crack the key.

        Asymmetric encryption algorithms, also known as public key encryption algorithms, mean that the encryption key and decryption key are completely different, one is the public key and the other is the private key, and it is impossible to deduce the other from either one. Its advantage is that it can adapt to an open use environment and can realize digital signature and verification. Its encryption and decryption process is shown in the figure below.

Process explanation:

1. Key generation phase:

   • The receiver generates a pair of keys: a public key and a private key.
   • The public key can be disclosed to others, and the private key must be kept secret.

2. Encryption stage:

   • The sender encrypts the data to be transmitted using the receiver's public key.
   • The sender can only use the public key for encryption and cannot decrypt the encrypted data.

3. Transfer stage:

   • The encrypted data is transmitted to the recipient through an insecure channel.

4. Decryption stage:

   • The receiver uses its own private key to decrypt the encrypted data.
   • Only the recipient has the private key and can decrypt the encrypted data.

Usage scenarios of asymmetric encryption and decryption:

1. Secure communications : Asymmetric encryption can be used to protect the transmission of sensitive information over unsecured networks. The sender encrypts the data using the recipient's public key, and only the recipient holding the private key can decrypt the data. This ensures the confidentiality and integrity of data during transmission.

2. Digital signatures : Asymmetric encryption can be used to generate and verify digital signatures to ensure data integrity and authentication. The sender uses his or her private key to sign the data, and the receiver uses the sender's public key to verify the authenticity of the signature.

3. Key Exchange : Asymmetric encryption can be used to securely exchange symmetric keys. The sender encrypts the symmetric key with the receiver's public key, and the receiver decrypts the symmetric key with its own private key. Afterwards, the sender and receiver can use the symmetric key to encrypt and decrypt the data for greater efficiency.

4. Authentication : Asymmetric encryption can be used for user authentication. Users can generate a key pair by storing the public key on the server. When a user logs in, the server encrypts a random challenge using the user's public key. The user uses the private key to decrypt the challenge and sends it back to the server to prove that he or she possesses the corresponding private key.

5. Security protocols : Asymmetric encryption is widely used in security protocols, such as SSL/TLS protocol for encrypting the transport layer communication of websites, SSH protocol for secure remote login and file transfer, and PGP (Pretty Good Privacy) protocol for email and file encryption, etc.

Advantages of asymmetric encryption and decryption:

1. Security : Asymmetric encryption algorithm provides higher security. Unlike symmetric encryption algorithms, asymmetric encryption uses a pair of associated keys, a public key and a private key. Public keys are used to encrypt data, while private keys are used to decrypt data or generate digital signatures. The private key remains secret and only the owner of the key can decrypt the data or generate a digital signature, thus protecting the confidentiality of the data.

2. Key Exchange : Asymmetric encryption algorithms can be used to securely exchange symmetric keys. In symmetric encryption, if the symmetric key is to be transmitted over an insecure communication channel, there is a risk of key disclosure. Asymmetric encryption algorithms, on the other hand, avoid this risk by using the other party's public key to encrypt the symmetric key and securely transmit the symmetric key to the communicating party.

3. Flexibility : Asymmetric encryption algorithms are more flexible in terms of key management and distribution. Since the public key can be shared publicly, key distribution is more convenient and suitable for multi-party communication and complex network environments.

Disadvantages of asymmetric encryption and decryption:

1. Computational complexity : Compared with symmetric encryption and decryption algorithms, asymmetric encryption and decryption algorithms have higher computational complexity. Due to the use of large number operations and complex mathematical algorithms, asymmetric encryption and decryption require more computing resources and time.

2. Slower processing speed : Due to the increase in computational complexity, the processing speed of asymmetric encryption and decryption is slow. Compared with symmetric encryption and decryption algorithms, under the same hardware environment, asymmetric encryption and decryption takes longer to complete encryption and decryption operations.

3. Long key length : In order to ensure sufficient security, the key length used in asymmetric encryption and decryption is usually longer. Long key lengths increase the cost of key storage and transmission, which may cause inconvenience to resource-constrained devices or network communications.

4. Difficulty in key management : Asymmetric encryption and decryption require the management and protection of two associated keys, namely the public key and the private key. For large-scale applications or complex network environments, the management process of key generation, distribution, storage, and revocation is relatively complex.

5. Security relies on private key protection : The security of asymmetric encryption and decryption relies on the protection of private keys. If the private key is leaked, lost or cracked, it will pose a major threat to the security of the system.

Common asymmetric encryption algorithms:

1. RSA (Rivest-Shamir-Adleman): RSA is one of the most commonly used asymmetric encryption algorithms. It is based on the difficult problem of large number decomposition and uses public and private keys for encryption and decryption operations.

2. Diffie-Hellman Key Exchange : The Diffie-Hellman key exchange algorithm is used to securely exchange symmetric keys over insecure communication channels. It allows two entities to negotiate a shared key without sharing the key.

3. Elliptic Curve Cryptography (ECC) : ECC is an asymmetric encryption algorithm based on elliptic curve theory. Compared with traditional asymmetric encryption algorithms, ECC can provide the same security but uses a shorter key length and is therefore more efficient on resource-constrained devices.

4. DSA (Digital Signature Algorithm) : DSA is an asymmetric encryption algorithm used for digital signatures. It is mainly used for authentication, data integrity protection and prevention of repudiation.

5. ECDSA (Elliptic Curve Digital Signature Algorithm) : ECDSA is a digital signature algorithm based on elliptic curves. Compared with RSA and DSA, it has a shorter key length and higher computational efficiency.