C#Base64简单加密与解密
作者：互联网
Base64属于简单加密算法的一种。类似于凯撒密码【它是一种替换加密的技术】
Base64字符串由65个字符组成，
大写字母A~Z，
小写字母a~z,
数字0~9，以及三个特殊字符+、/、=
【=“等号”用于补充字符，使Base64字符串长度变成4的倍数】
规则
考虑到初始源字符串可能是任何文本编码的【中文GBK，Unicode，ASCII等】，因此Base64字符串加密只处理字节数组【字节数组通过encoding.GetBytes(string src)获得】。
Base64编码字符串的长度一定是4的倍数。
Base64要求把每三个8Bit的字节转换为四个6Bit的字节（3*8 = 4*6 = 24），然后把6Bit再添两位高位0，组成四个8Bit的字节，因此每个Base64字节的十进制范围为0~63。也就是说，转换后的字符串理论上将要比原来的长1/3。
字节数组的长度应该是3的倍数，如果这个条件不能满足的话，具体的解决办法是这样的：原文剩余的字节根据编码规则继续单独转(1变2，2变3；不够的位数用0补全)，再用=号补满4个字节。这就是为什么有些Base64编码会以一个或两个等号结束的原因，但等号最多只有两个。因为一个原字节至少会变成两个目标字节，所以余数任何情况下都只可能是0，1，2这三个数中的一个。如果余数是0的话，就表示原文字节数正好是3的倍数（最理想的情况）。如果是1的话，转成2个Base64编码字符，为了让Base64编码是4的倍数，就要补2个等号；同理，如果是2的话，就要补1个等号。
6Bit数字【0~63】映射Base64字符表如下
| 索引 | 对应字符 | 索引 | 对应字符 | 索引 | 对应字符 | 索引 | 对应字符 |
| 0 | A | 17 | R | 34 | i | 51 | z |
| 1 | B | 18 | S | 35 | j | 52 | 0 |
| 2 | C | 19 | T | 36 | k | 53 | 1 |
| 3 | D | 20 | U | 37 | l | 54 | 2 |
| 4 | E | 21 | V | 38 | m | 55 | 3 |
| 5 | F | 22 | W | 39 | n | 56 | 4 |
| 6 | G | 23 | X | 40 | o | 57 | 5 |
| 7 | H | 24 | Y | 41 | p | 58 | 6 |
| 8 | I | 25 | Z | 42 | q | 59 | 7 |
| 9 | J | 26 | a | 43 | r | 60 | 8 |
| 10 | K | 27 | b | 44 | s | 61 | 9 |
| 11 | L | 28 | c | 45 | t | 62 | + |
| 12 | M | 29 | d | 46 | u | 63 | / |
| 13 | N | 30 | e | 47 | v | ||
| 14 | O | 31 | f | 48 | w | ||
| 15 | P | 32 | g | 49 | x | ||
| 16 | Q | 33 | h | 50 | y |
测试Base64源程序
新建WinForm应用程序Base64EncoderDemo，重命名默认的 Form1为FormBase64Encoder，
窗体FormBase64Encoder设计如图：
FormBase64Encoder.cs主要代码如下
（忽略设计器自动生成的代码）：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Base64EncoderDemo
{
public partial class FormBase64Encoder : Form
{
public FormBase64Encoder()
{
InitializeComponent();
//参考Convert微软源程序
//https://referencesource.microsoft.com/#mscorlib/system/convert.cs,fc990bd1275d43d6
}
private void FormBase64Encoder_Load(object sender, EventArgs e)
{
rtxtMessage.ReadOnly = true;
//编码格式
cboEncoding.Items.AddRange(new string[] { "ASCII", "Unicode", "UTF-8", "GBK" });
cboEncoding.SelectedIndex = 0;
}
private void btnClear_Click(object sender, EventArgs e)
{
rtxtSourceString.Clear();
rtxtBase64String.Clear();
rtxtMessage.Clear();
}
/// <summary>
/// 显示提示消息
/// </summary>
/// <param name="content"></param>
private void DisplayMessage(string content)
{
if (rtxtMessage.TextLength >= 20480)
{
rtxtMessage.Clear();
}
rtxtMessage.AppendText($"{DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss.fff")} -> {content}\n");
rtxtMessage.ScrollToCaret();
}
private void btnConvertBase64_Click(object sender, EventArgs e)
{
rtxtBase64String.Clear();
if (rtxtSourceString.Text.Trim().Length == 0)
{
rtxtSourceString.Focus();
DisplayMessage("源字符串不能为空");
return;
}
try
{
Encoding encoding = Encoding.GetEncoding(cboEncoding.Text);
byte[] buffer = encoding.GetBytes(rtxtSourceString.Text.Trim());
rtxtBase64String.Text = Convert.ToBase64String(buffer, Base64FormattingOptions.None);
DisplayMessage($"转换成功，Base64字符串【{rtxtBase64String.Text}】");
}
catch (Exception ex)
{
DisplayMessage($"转换为Base64时出错：【{ex.Message}】");
}
}
private void btnRestore_Click(object sender, EventArgs e)
{
rtxtSourceString.Clear();
if (rtxtBase64String.Text.Trim().Length == 0)
{
rtxtBase64String.Focus();
DisplayMessage("Base64字符串不能为空");
return;
}
try
{
Encoding encoding = Encoding.GetEncoding(cboEncoding.Text);
byte[] buffer = Convert.FromBase64String(rtxtBase64String.Text);
rtxtSourceString.Text = encoding.GetString(buffer);
DisplayMessage($"还原成功，源字符串【{rtxtSourceString.Text}】");
}
catch (Exception ex)
{
DisplayMessage($"还原字符串时出错：【{ex.Message}】");
}
}
}
}
程序运行如图：
参考微软源代码：Reference Source
public static unsafe String ToBase64String(byte[] inArray, int offset, int length, Base64FormattingOptions options) {
//Do data verfication
if (inArray==null)
throw new ArgumentNullException("inArray");
if (length<0)
throw new ArgumentOutOfRangeException("length", Environment.GetResourceString("ArgumentOutOfRange_Index"));
if (offset<0)
throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_GenericPositive"));
if (options < Base64FormattingOptions.None || options > Base64FormattingOptions.InsertLineBreaks)
throw new ArgumentException(Environment.GetResourceString("Arg_EnumIllegalVal", (int)options));
Contract.Ensures(Contract.Result<string>() != null);
Contract.EndContractBlock();
int inArrayLength;
int stringLength;
inArrayLength = inArray.Length;
if (offset > (inArrayLength - length))
throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_OffsetLength"));
if (inArrayLength == 0)
return String.Empty;
bool insertLineBreaks = (options == Base64FormattingOptions.InsertLineBreaks);
//Create the new string. This is the maximally required length.
stringLength = ToBase64_CalculateAndValidateOutputLength(length, insertLineBreaks);
string returnString = string.FastAllocateString(stringLength);
fixed (char* outChars = returnString){
fixed (byte* inData = inArray) {
int j = ConvertToBase64Array(outChars,inData,offset,length, insertLineBreaks);
BCLDebug.Assert(returnString.Length == j, "returnString.Length == j");
return returnString;
}
}
}
Base64处理字节数组逻辑函数
internal static readonly char[] base64Table = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O',
'P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d',
'e','f','g','h','i','j','k','l','m','n','o','p','q','r','s',
't','u','v','w','x','y','z','0','1','2','3','4','5','6','7',
'8','9','+','/','=' };
private const Int32 base64LineBreakPosition = 76; [System.Security.SecurityCritical] // auto-generated
private static unsafe int ConvertToBase64Array(char* outChars, byte* inData, int offset, int length, bool insertLineBreaks) {
int lengthmod3 = length%3;
int calcLength = offset + (length - lengthmod3);
int j=0;
int charcount = 0;
//Convert three bytes at a time to base64 notation. This will consume 4 chars.
int i;
// get a pointer to the base64Table to avoid unnecessary range checking
fixed(char* base64 = base64Table) {
for (i=offset; i<calcLength; i+=3)
{
if (insertLineBreaks) {
if (charcount == base64LineBreakPosition) {
outChars[j++] = '\r';
outChars[j++] = '\n';
charcount = 0;
}
charcount += 4;
}
outChars[j] = base64[(inData[i]&0xfc)>>2];
outChars[j+1] = base64[((inData[i]&0x03)<<4) | ((inData[i+1]&0xf0)>>4)];
outChars[j+2] = base64[((inData[i+1]&0x0f)<<2) | ((inData[i+2]&0xc0)>>6)];
outChars[j+3] = base64[(inData[i+2]&0x3f)];
j += 4;
}
//Where we left off before
i = calcLength;
if (insertLineBreaks && (lengthmod3 !=0) && (charcount == base64LineBreakPosition)) {
outChars[j++] = '\r';
outChars[j++] = '\n';
}
switch(lengthmod3)
{
case 2: //One character padding needed
outChars[j] = base64[(inData[i]&0xfc)>>2];
outChars[j+1] = base64[((inData[i]&0x03)<<4)|((inData[i+1]&0xf0)>>4)];
outChars[j+2] = base64[(inData[i+1]&0x0f)<<2];
outChars[j+3] = base64[64]; //Pad
j+=4;
break;
case 1: // Two character padding needed
outChars[j] = base64[(inData[i]&0xfc)>>2];
outChars[j+1] = base64[(inData[i]&0x03)<<4];
outChars[j+2] = base64[64]; //Pad
outChars[j+3] = base64[64]; //Pad
j+=4;
break;
}
}
return j;
}
private static int ToBase64_CalculateAndValidateOutputLength(int inputLength, bool insertLineBreaks) {
long outlen = ((long)inputLength) / 3 * 4; // the base length - we want integer division here.
outlen += ((inputLength % 3) != 0) ? 4 : 0; // at most 4 more chars for the remainder
if (outlen == 0)
return 0;
if (insertLineBreaks) {
long newLines = outlen / base64LineBreakPosition;
if ((outlen % base64LineBreakPosition) == 0) {
--newLines;
}
outlen += newLines * 2; // the number of line break chars we'll add, "\r\n"
}
// If we overflow an int then we cannot allocate enough
// memory to output the value so throw
if (outlen > int.MaxValue)
throw new OutOfMemoryException();
return (int)outlen;
}标签：inData,字节,C#,Text,Base64,解密,int,outChars 来源： https://blog.csdn.net/ylq1045/article/details/121621133