Always use encryption to protect sensitive data in .NET Core applications. Encryption is the process of converting plain text into cipher text, which can only be read by authorized parties who have the decryption key. Sensitive data includes personal information, financial data, and any other data that could be used to harm individuals or organizations if it falls into the wrong hands. Encryption is an essential security measure that helps to prevent data breaches and protect the privacy of users.

.NET Core provides several encryption algorithms that can be used to protect sensitive data. These algorithms include AES, RSA, and TripleDES. AES is the most widely used encryption algorithm and is recommended for most applications. RSA is used for asymmetric encryption, where the encryption and decryption keys are different. TripleDES is an older encryption algorithm that is still used in some legacy applications.

To use encryption in .NET Core, you can use the System.Security.Cryptography namespace, which provides classes for implementing encryption and decryption. For example, to encrypt a string using AES encryption, you can use the AesManaged class as follows:

using System;
using System.Security.Cryptography;
using System.Text;

public static string EncryptString(string plainText, byte[] key, byte[] iv)
{
    using (AesManaged aes = new AesManaged())
    {
        aes.Key = key;
        aes.IV = iv;

        ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

        using (MemoryStream ms = new MemoryStream())
        {
            using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
            {
                using (StreamWriter sw = new StreamWriter(cs))
                {
                    sw.Write(plainText);
                }
                return Convert.ToBase64String(ms.ToArray());
            }
        }
    }
}

In the above example, the EncryptString method takes a plain text string, a key, and an initialization vector (IV) as input parameters. The method creates an instance of the AesManaged class, sets the key and IV, and creates an encryptor object using the CreateEncryptor method. The method then writes the plain text to a memory stream using a CryptoStream object and returns the encrypted string as a base64-encoded string.