C#でファイルのAES暗号化

ファイル暗号化クラス

ファイルの暗号化、復号化を行うためのクラス。

引数には、それぞれ入力ファイルストリーム、出力ファイルストリーム、パスワードを入力。

FileEncryptor

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

namespace EncryptTest
{
    /// <summary>
    /// File Encryptor Class
    /// </summary>
    public static class FileEncryptor
    {
        /// <summary>
        /// Key Length
        /// </summary>
        public const int KeyLength = 16;

        /// <summary>
        /// Generate Byte Key from Password
        /// </summary>
        /// <returns>Byte Key</returns>
        /// <param name="password">Password</param>
        private static byte[] GenerateByteKey(string password)
        {
            /* Get Bytes of Password */
            var bytesPassword = Encoding.UTF8.GetBytes(password);
            /* Create Bytes Key Array */
            var bytesKey = new byte[KeyLength];

            /* Loop to Key Length */
            for(int i = 0; i < KeyLength; i++)
            {
                /* Copy Password Byte Array and fill remain bytes by 0 */
                bytesKey[i] = (i < bytesPassword.Length) ? bytesPassword[i] : (byte)0;
            }

            return bytesKey;
        }

        /// <summary>
        /// Encrypt File
        /// </summary>
        /// <param name="ifs">Input File Stream</param>
        /// <param name="ofs">Output File Stream</param>
        /// <param name="password">Password</param>
        public static void Encrypt(Stream ifs, Stream ofs, string password)
        {
            /* Generate Byte Key from Password */
            var bytesKey = FileEncryptor.GenerateByteKey(password);

            /* Create AES Crypto Service Provider */
            var aes = new AesCryptoServiceProvider() {
                BlockSize = 128,
                KeySize = 128,
                Mode = CipherMode.CBC,
                Padding = PaddingMode.PKCS7,
                Key = bytesKey,
            };

            /* Generate Random Initialization Vector(IV) */
            aes.GenerateIV();

            /* Get IV */
            var bytesIV = aes.IV;

            /* Write IV to File (128bit=16bytes) */
            ofs.Write(bytesIV, 0, 16);

            /* Create AES Encryptor */
            using(var encrypt = aes.CreateEncryptor())
            {
                /* Create Crypto Stream */
                using(var cs = new CryptoStream(ofs, encrypt, CryptoStreamMode.Write))
                {
                    /* Inifity Loop */
                    while(true)
                    {
                        /* Create Write Buffer */
                        var buffer = new byte[1024];
                        /* Read File to Buffer */
                        var len = ifs.Read(buffer, 0, buffer.Length);

                        /* Read Data Size is larger than 0 */
                        if(len > 0)
                        {
                            /* Write Read Data to Crypto Stream */
                            cs.Write(buffer, 0, len);
                        }
                        else
                        {
                            /* End of Input File */
                            break;
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Decrypt File
        /// </summary>
        /// <param name="ifs">Input File Stream</param>
        /// <param name="ofs">Output File Stream</param>
        /// <param name="password">Password</param>
        public static void Decrypt(Stream ifs, Stream ofs, string password)
        {
            /* Generate Byte Key from Password */
            var bytesKey = FileEncryptor.GenerateByteKey(password);

            /* Create AES Crypto Service Provider */
            var aes = new AesCryptoServiceProvider() {
                BlockSize = 128,
                KeySize = 128,
                Mode = CipherMode.CBC,
                Padding = PaddingMode.PKCS7,
                Key = bytesKey,
            };

            /* Create IV Buffer */
            var bytesIV = new byte[KeyLength];

            /* Read IV from Input File */
            ifs.Read(bytesIV, 0, KeyLength);

            /* Set Read IV */
            aes.IV = bytesIV;

            /* Create AES Decryptor */
            using(var encrypt = aes.CreateDecryptor())
            {
                /* Create Crypto Stream */
                using(var cs = new CryptoStream(ofs, encrypt, CryptoStreamMode.Write))
                {
                    /* Inifinity Loop */
                    while(true)
                    {
                        /* Create Read Buffer */
                        var buffer = new byte[1024];

                        /* Read Input File to Buffer */
                        var len = ifs.Read(buffer, 0, buffer.Length);

                        /* Read Data Size is larger than 0 */
                        if(len > 0)
                        {
                            /* Write Read Data to Crypto Stream */
                            cs.Write(buffer, 0, len);
                        }
                        else
                        {
                            /* End of Data */
                            break;
                        }
                    }
                }
            }
        }
    }
}

Usage

使い方は、
1. 入力ファイル(平文)、出力ファイル(暗号化ファイル)のストリームを生成し、暗号化用パスワードを入力してファイルを暗号化
2. 入力ファイル(暗号化ファイル)、出力ファイル(復号化ファイル)のストリームを生成し、暗号化に使用したパスワードを入力してファイルを復号化

Program.cs

class MainClass
{
    public static void Main(string[] args)
    {   
        /* Create Input File Stream */
        using(var eifs = new FileStream("InputFile.txt", FileMode.Open, FileAccess.Read))
        {
            /* Create Output File Stream*/
            using(var eofs = new FileStream("EncryptedFile.bin", FileMode.Create, FileAccess.Write))
            {
                /* Encrypt File */
                FileEncryptor.Encrypt(eifs, eofs, "Password");
            }
        }

        /* Create Input File Stream */
        using(var difs = new FileStream("EncryptedFile.bin", FileMode.Open, FileAccess.Read))
        {
            /* Create Output File Stream*/
            using(var dofs = new FileStream("DecryptedFile.txt", FileMode.Create, FileAccess.Write))
            {
                /* Decrypt File */
                FileEncryptor.Decrypt(difs, dofs, "Password");
            }
        }
    }
}