C# AES暗号化（開発者向けの仕組み）

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

class Program
{
    // Declare a static byte array for encrypted data
    public static byte[] encryptedData;

    // Main method to demonstrate encryption and decryption
    public static void Main(string[] args)
    {
        // String plaintext to be encrypted
        string plaintext = "This is some sensitive data!";
        string key = "abcdefghijklmnop"; // 128-bit key (16 characters)

        // Encrypt the plaintext
        string ciphertext = Encrypt(plaintext, key);
        Console.WriteLine("Encrypted Data: " + ciphertext);

        // Decrypt the ciphertext
        string decryptedData = Decrypt(ciphertext, key);
        Console.WriteLine("Decrypted Data: " + decryptedData);
    }

    // Method to encrypt data
    public static string Encrypt(string plaintext, string key)
    {
        // Create a new instance of the AES encryption algorithm
        using (Aes aes = Aes.Create())
        {
            aes.Key = Encoding.UTF8.GetBytes(key);
            aes.IV = new byte[16]; // Initialization vector (IV)

            // Create an encryptor to perform the stream transform
            ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

            // Create the streams used for encryption
            using (MemoryStream ms = new MemoryStream())
            {
                // Create a CryptoStream using the encryptor
                using (CryptoStream cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
                {
                    using (StreamWriter sw = new StreamWriter(cs))
                    {
                        sw.Write(plaintext);
                    }
                }
                // Store the encrypted data in the public static byte array
                encryptedData = ms.ToArray();
                return Convert.ToBase64String(encryptedData);
            }
        }
    }

    // Method to decrypt data
    public static string Decrypt(string ciphertext, string key)
    {
        using (Aes aes = Aes.Create())
        {
            aes.Key = Encoding.UTF8.GetBytes(key);
            aes.IV = new byte[16]; // Initialization vector (IV)

            // Create a decryptor to perform the stream transform
            ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);

            // Create the streams used for decryption
            using (MemoryStream ms = new MemoryStream(Convert.FromBase64String(ciphertext)))
            {
                using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
                {
                    using (StreamReader sr = new StreamReader(cs))
                    {
                        return sr.ReadToEnd();
                    }
                }
            }
        }
    }
}

Imports System
Imports System.IO
Imports System.Security.Cryptography
Imports System.Text

Friend Class Program
	' Declare a static byte array for encrypted data
	Public Shared encryptedData() As Byte

	' Main method to demonstrate encryption and decryption
	Public Shared Sub Main(ByVal args() As String)
		' String plaintext to be encrypted
		Dim plaintext As String = "This is some sensitive data!"
		Dim key As String = "abcdefghijklmnop" ' 128-bit key (16 characters)

		' Encrypt the plaintext
		Dim ciphertext As String = Encrypt(plaintext, key)
		Console.WriteLine("Encrypted Data: " & ciphertext)

		' Decrypt the ciphertext
		Dim decryptedData As String = Decrypt(ciphertext, key)
		Console.WriteLine("Decrypted Data: " & decryptedData)
	End Sub

	' Method to encrypt data
	Public Shared Function Encrypt(ByVal plaintext As String, ByVal key As String) As String
		' Create a new instance of the AES encryption algorithm
		Using aes As Aes = System.Security.Cryptography.Aes.Create()
			aes.Key = Encoding.UTF8.GetBytes(key)
			aes.IV = New Byte(15){} ' Initialization vector (IV)

			' Create an encryptor to perform the stream transform
			Dim encryptor As ICryptoTransform = aes.CreateEncryptor(aes.Key, aes.IV)

			' Create the streams used for encryption
			Using ms As New MemoryStream()
				' Create a CryptoStream using the encryptor
				Using cs As New CryptoStream(ms, encryptor, CryptoStreamMode.Write)
					Using sw As New StreamWriter(cs)
						sw.Write(plaintext)
					End Using
				End Using
				' Store the encrypted data in the public static byte array
				encryptedData = ms.ToArray()
				Return Convert.ToBase64String(encryptedData)
			End Using
		End Using
	End Function

	' Method to decrypt data
	Public Shared Function Decrypt(ByVal ciphertext As String, ByVal key As String) As String
		Using aes As Aes = System.Security.Cryptography.Aes.Create()
			aes.Key = Encoding.UTF8.GetBytes(key)
			aes.IV = New Byte(15){} ' Initialization vector (IV)

			' Create a decryptor to perform the stream transform
			Dim decryptor As ICryptoTransform = aes.CreateDecryptor(aes.Key, aes.IV)

			' Create the streams used for decryption
			Using ms As New MemoryStream(Convert.FromBase64String(ciphertext))
				Using cs As New CryptoStream(ms, decryptor, CryptoStreamMode.Read)
					Using sr As New StreamReader(cs)
						Return sr.ReadToEnd()
					End Using
				End Using
			End Using
		End Using
	End Function
End Class