Add project files.

EncryptionTest.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

EncryptionTest.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.7.34031.279
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EncryptionTest", "EncryptionTest.csproj", "{A549CEB8-0D68-441D-8C82-85E96B255731}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{A549CEB8-0D68-441D-8C82-85E96B255731}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A549CEB8-0D68-441D-8C82-85E96B255731}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A549CEB8-0D68-441D-8C82-85E96B255731}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A549CEB8-0D68-441D-8C82-85E96B255731}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {A55FDA6C-4374-42C6-B539-86D24B42672B}
+	EndGlobalSection
+EndGlobal

Program.cs

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+using System.Security.Cryptography;
+using System.Text;
+
+static string Encrypt(string plainText, byte[] secretKey) {
+	using Aes aes = Aes.Create();
+	aes.Key = secretKey;
+
+	// Convert the plain text string into a byte array
+	byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
+
+	// Create an encryptor using the AES service and its initialization vector (IV)
+	ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
+
+	// Perform the encryption
+	byte[] encrypted = encryptor.TransformFinalBlock(plainTextBytes, 0, plainTextBytes.Length);
+
+	// Create a new byte array to hold the IV and the encrypted data
+	byte[] result = new byte[aes.IV.Length + encrypted.Length];
+
+	// Copy the IV and encrypted data into the result byte array
+	Buffer.BlockCopy(aes.IV,    0, result, 0,             aes.IV.Length);
+	Buffer.BlockCopy(encrypted, 0, result, aes.IV.Length, encrypted.Length);
+
+	return Convert.ToBase64String(result);
+}
+
+static string Decrypt(string encryptedText, byte[] secretKey) {
+	using Aes aes = Aes.Create();
+	aes.Key = secretKey;
+
+	// Decode the base64 string into a byte array
+	byte[] fullCipher = Convert.FromBase64String(encryptedText);
+
+	// Create byte arrays to hold the IV and the encrypted data
+	byte[] iv = new byte[aes.BlockSize / 8];
+	byte[] cipher = new byte[fullCipher.Length - iv.Length];
+
+	// Copy the IV and encrypted data from the full cipher byte array
+	Buffer.BlockCopy(fullCipher, 0, iv, 0, iv.Length);
+	Buffer.BlockCopy(fullCipher, iv.Length, cipher, 0, cipher.Length);
+
+	// Assign the IV to the AES service
+	aes.IV = iv;
+
+	// Create a decryptor using the AES service
+	ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
+
+	// Perform the decryption
+	byte[] decrypted = decryptor.TransformFinalBlock(cipher, 0, cipher.Length);
+
+	// Convert the decrypted byte array back into a string
+	return Encoding.UTF8.GetString(decrypted);
+}
+
+
+Console.WriteLine("Hello, World!");
+
+string key = "REDACTED_BASE64_STRING";
+byte[] secretKey = Convert.FromBase64String(key);
+
+try {
+	string input = "Hello, world!";
+	Console.WriteLine("Original text: " + input);
+
+	string encryptedText = Encrypt(input, secretKey);
+	Console.WriteLine("Encrypted text: " + encryptedText);
+
+	string decrypted = Decrypt(encryptedText, secretKey);
+	Console.WriteLine("Decrypted text: " + decrypted);
+} catch (Exception e) {
+	Console.WriteLine(e);
+}