加密

1.MD5加密

//採用重載public byte[] ComputeHash(byte[] buffer)
//其餘重載public byte[] ComputeHash(Stream inputStream)，
//其餘重載public byte[] ComputeHash(byte[] buffer,int offset,int count)
public static string GetMD5Hash(string str)
{
    MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();//MD5 md5 =
    byte[] bytes = ASCIIEncoding.Default.GetBytes(str);//System.Text.Encoding.Default.GetBytes(str)
    byte[] encoded = md5.ComputeHash(bytes);//計算 bytes字節數組的哈希值

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < encoded.Length; i++)
        sb.Append(encoded[i].ToString("x2"));//ToString("x").PadLeft(2, '0'); //對遍歷到的字節進行加密

    return sb.ToString();
}

public static string GetMD5Hash2(string str)
{
    System.Security.Cryptography.MD5 md5 = System.Security.Cryptography.MD5.Create();
    byte[] bytes = Encoding.Default.GetBytes(str);
    byte[] encoded = md5.ComputeHash(bytes);

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < encoded.Length; i++)
        sb.Append(encoded[i].ToString("x2"));

    return sb.ToString();
}

System.Security.Cryptography.MD5.Create() is actually creating a MD5CryptoServiceProvider.
MD5 is the base class and it's abstract. I'm guessing they added the public create function for ease of use.

public sealed class MD5CryptoServiceProvider : MD5
public abstract class MD5 : HashAlgorithm

MD5 Represents the abstract class from which all implementations of the MD5 hash algorithm inherit.
MD5CryptoServiceProvider Computes the MD5 hash value for the input data using the implementation provided by the cryptographic service provider (CSP). This class cannot be inherited.

2.ROT13

private string ROT13Encode(string input)
{
    char tem_char;
    int uniChar;
    StringBuilder encodeText=new StringBuilder();
    for (int i = 0; i < input.Length; i++)
    {
        //https://msdn.microsoft.com/en-us/library/362314fe.aspx
        tem_char = input[i];//System.Convert.ToChar(input.Substring(i,1));
        uniChar = (int) tem_char;
        if (uniChar >= 97 && uniChar <= 109)//97...109 a...m
        {
            uniChar = uniChar + 13;//110...122 n...z
        }
        else if (uniChar >= 110 && uniChar <= 122)
            {
                uniChar = uniChar - 13;
            }
        else if (uniChar >= 65 && uniChar <= 77)
        {
            uniChar = uniChar + 13;
        }
        else if (uniChar >= 78 && uniChar <= 909)
        {
            uniChar = uniChar - 13;
        }
        encodeText.Append((char) uniChar);
    }
    return encodeText.ToString();
}