Writing Simple Encrypt and Decrypt Utility Methods in C#
by Jeffrey Sward
 
Requirements
 
  • Encryption for visual inspection only (human pencil-and-paper)
  • Does not need to be secure from high volume automatic attack
  • Simple method calls: pass plain text string, return cipher text string, and pass cipher text string, return plain text string
  • Wrap in utility form for reuse
 
Issues
 
  • System.Security.Cryptography is very versatile, but requires excessive parameterization
  • Cryptographic functions operate on byte array of integers rather than string of ASCII characters
  • Conversion from string to byte array necessary
  • Conversion from ASCII to binary byte necessary
  • Cryptographic functions operate on memory stream objects rather than simple strings
  • Two arrays of integers are needed in addition to text: key and initialization vector
 
Solution
 
  • Select AES method because of least amount of complexity from options in System.Security.Cryptography
  • Hard code constant arrays of byte integers fro key and initialization vector. This is sufficient for protection from human pencil-and-paper encryption
  • Simple string-to-string methods for encryption and decryption
  • All conversions handled within methods, allowing for passing and receiving plain text strings and cipher strings only.
 
Code Sample Encrypt
 

using System;
using System.Collections.Generic;
using System.Text;
using System.Diagnostics;
using System.Reflection;
using System.Security.Cryptography;
using System.IO;

public static String Encrypt(String plainTextString)
    {
      String cipherTextString = String.Empty;
      try
      {
        WebUtilities.GenericLogHandler.Info
          (
               WebUtilities.GlobalConstants.Entry
             + typeof(GenericCryptographicHandler).FullName.ToString()
             + WebUtilities.GlobalConstants.Dot
             + MethodBase.GetCurrentMethod().Name
          );
        WebUtilities.GenericLogHandler.Debug
          (
              WebUtilities.GlobalConstants.PlainText
            + plainTextString
          );
        byte[] plainTextByte = Encoding.UTF8.GetBytes(plainTextString);
        byte[] cipherTextByte = null;
        using (Aes cryptographicAlgorithm = Aes.Create())
        {
          using (ICryptoTransform encryptor
            = cryptographicAlgorithm.CreateEncryptor
              (GlobalConstants.DefaultCryptographicKey
             , GlobalConstants.DefaultCryptographicInitializationVector))
          {
            MemoryStream encryptMemoryStream = new MemoryStream();
            using (Stream encryptCryptoStream
              = new CryptoStream(encryptMemoryStream, encryptor, CryptoStreamMode.Write))
            {
              encryptCryptoStream.Write(plainTextByte, 0, plainTextByte.Length);
            }
            cipherTextByte = encryptMemoryStream.ToArray();
          }
        }
        cipherTextString = Convert.ToBase64String(cipherTextByte);
        if (cipherTextString == null)
        {
          cipherTextString = GlobalConstants.Null;
        }
        WebUtilities.GenericLogHandler.Debug
          (
               WebUtilities.GlobalConstants.CipherText
             + cipherTextString
           );
        WebUtilities.GenericLogHandler.Info
          (
               WebUtilities.GlobalConstants.Exit
             + typeof(GenericCryptographicHandler).FullName.ToString()
             + WebUtilities.GlobalConstants.Dot
             + MethodBase.GetCurrentMethod().Name
          );
      }
      catch (Exception ex)
      {
        WebUtilities.GenericErrorHandler.HandleError(ex);
      }
     return cipherTextString;
    }

 
Code Sample Decrypt
 

    public static String Decrypt(String cipherTextString)
    {
      String plainTextString = String.Empty;
      try
      {
        WebUtilities.GenericLogHandler.Info
          (
               WebUtilities.GlobalConstants.Entry
             + typeof(GenericCryptographicHandler).FullName.ToString()
             + WebUtilities.GlobalConstants.Dot
             + MethodBase.GetCurrentMethod().Name
          );
        WebUtilities.GenericLogHandler.Debug
          (
              WebUtilities.GlobalConstants.CipherText
            + cipherTextString
          );
        byte[] cipherTextByte = Convert.FromBase64String(cipherTextString);
        byte[] plainTextByte = null;
        using (Aes cryptographicAlgorithm = Aes.Create())
        {
          using (ICryptoTransform decryptor
            = cryptographicAlgorithm.CreateDecryptor
              (GlobalConstants.DefaultCryptographicKey
             , GlobalConstants.DefaultCryptographicInitializationVector))
          {
            MemoryStream decryptMemoryStream = new MemoryStream();
            using (Stream decryptCryptoStream
              = new CryptoStream(decryptMemoryStream, decryptor, CryptoStreamMode.Write))
            {
              decryptCryptoStream.Write(cipherTextByte, 0, cipherTextByte.Length);
            }
            plainTextByte = decryptMemoryStream.ToArray();
          }
        }
        plainTextString = Encoding.UTF8.GetString(plainTextByte);
        if (plainTextString == null)
        {
          plainTextString = GlobalConstants.Null;
        }
        WebUtilities.GenericLogHandler.Debug
          (
               WebUtilities.GlobalConstants.CipherText
             + cipherTextString
           );
        WebUtilities.GenericLogHandler.Info
          (
               WebUtilities.GlobalConstants.Exit
             + typeof(GenericCryptographicHandler).FullName.ToString()
             + WebUtilities.GlobalConstants.Dot
             + MethodBase.GetCurrentMethod().Name
          );
      }
      catch (Exception ex)
      {
        WebUtilities.GenericErrorHandler.HandleError(ex);
      }
      return plainTextString;
    }

 
Code Sample Cryptographic Constants
 

// use random numbers between 0 and 255 rather than the values shown

public static readonly byte[] DefaultCryptographicKey = {1 ,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};

public static readonly byte[] DefaultCryptographicInitializationVector = {101 ,102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116};

 
 

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