C# - AES128で1ブロックだけ暗号化する

概要

AES128で16byteのbyte配列を暗号化・復号するサンプルコードです。
※セキュアなコーディングとかは詳しくないので、正式なものに使うのに耐えれるかは保証できません。

ソースコード

AES128Sample.cs

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

class AES128Sample
{
    [STAThread]
    static void Main(string[] args)
    {
        byte[] plain = new byte[]{0x00,0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88,0x99,0xaa,0xbb,0xcc,0xdd,0xee,0xff};
        byte[] key   = new byte[]{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0a,0x0b,0x0c,0x0d,0x0e,0x0f};

        byte[] cipher;
        cipher = Encrypt1BlockAes128(plain, key);
        DumpArray(cipher);
        DumpArray(Decrypt1BlockAes128(cipher, key));
    }

    static void DumpArray(byte[] a)
    {
        for ( int i=0; i<a.Length; i++ ) {
            Console.Write(a[i].ToString("X02"));
        }
        Console.WriteLine();
    }

    static byte[] Decrypt1BlockAes128(byte[] cipher, byte[] key)
    {
        return EncDec1BlockAes128(cipher, key, false);
    }
    
    static byte[] Encrypt1BlockAes128(byte[] plain, byte[] key)
    {
        return EncDec1BlockAes128(plain, key, true);
    }

    static byte[] EncDec1BlockAes128(byte[] a, byte[] key, bool isEncryptMode)
    {
        const int N = 16; // 128bit = 16bytes

        if ( a == null || key == null ) {
            throw new ArgumentNullException();
        }
        if ( a.Length != N || key.Length != N ) {
            throw new ArgumentException();
        }

        byte[] buf = new byte[N];

        //using (AesManaged aes = new AesManaged()) // obsoleted
        using (Aes aes = Aes.Create())
        {
            aes.BlockSize = N*8;
            aes.Key = key;
            aes.IV = new byte[N]; // all zero. refer to https://docs.microsoft.com/ja-jp/dotnet/csharp/programming-guide/arrays/single-dimensional-arrays
            aes.Mode = CipherMode.ECB;
            aes.Padding = PaddingMode.None;
            ICryptoTransform encryptorOrDecryptor;
            if ( isEncryptMode ) {
                encryptorOrDecryptor = aes.CreateEncryptor(aes.Key, aes.IV);
            }
            else {
                encryptorOrDecryptor = aes.CreateDecryptor(aes.Key, aes.IV);
            }

            using (var ms = new MemoryStream(a))
            using (var cs = new CryptoStream(ms, encryptorOrDecryptor, CryptoStreamMode.Read))
            {
                cs.Read(buf, 0, N);
            }
        }
        return buf;
    }
}

検算

Test Vector的なやつ

FIPS-197 の C.1 AES-128 (Nk=4, Nr=10)

PLAINTEXT: 00112233445566778899aabbccddeeff
KEY: 000102030405060708090a0b0c0d0e0f
round[10].output 69c4e0d86a7b0430d8cdb78070b4c55a

参考サイト

• MS Doc - AES class
• 暗号利用モード - Wikipedia
• FIPS-197