C# 加密–RSA前端与后台的加密&解密

1. 前言

本问是根据网上很多文章的总结得到的。

2. 介绍

RSA加密算法是一种非对称加密算法。

对极大整数做因数分解的难度决定了RSA算法的可靠性。换言之，对一极大整数做因数分解愈困难，RSA算法愈可靠。假如有人找到一种快速因数分解的算法的话，那么用RSA加密的信息的可靠性就肯定会极度下降。但找到这样的算法的可能性是非常小的。今天只有短的RSA钥匙才可能被强力方式解破。到2016年为止，世界上还没有任何可靠的攻击RSA算法的方式。只要其钥匙的长度足够长，用RSA加密的信息实际上是不能被解破的。

1983年麻省理工学院在美国为RSA算法申请了专利。这个专利2000年9月21日失效。由于该算法在申请专利前就已经被发表了，在世界上大多数其它地区这个专利权不被承认。

具体介绍可以查看维基百科

https://zh.wikipedia.org/wiki/RSA%E5%8A%A0%E5%AF%86%E6%BC%94%E7%AE%97%E6%B3%95

3. 开始

1）在线RSA加密，请选用PKCS#1来生成公钥与私钥

http://web.chacuo.net/netrsakeypair

点击【生成秘钥对RSA】就可以生成对应的非对称加密公钥与非对称加密似钥

2）前端JS框架

http://travistidwell.com/jsencrypt/

3）流程图

从上图可以看到，先从网站上生成publicKey与privateKey。

第一步返回publicKey前端，用来对password等敏感字段的加密。

第二步，前端进行password敏感字段的加密。

第三步post数据给后端。

第四步用publicKey与privateKey进行解密。

4.代码

这里的代码是简单的直接从前端访问后台，后台进行解密。逻辑根据读者的爱好编写。

前端代码

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
<script src="http://code.jquery.com/jquery-1.8.3.min.js"></script>
<script src="http://passport.cnblogs.com/scripts/jsencrypt.min.js"></script>
<script type="text/javascript">
// 使用jsencrypt类库加密js方法，
function encryptRequest(reqUrl, data, publicKey) {
var encrypt = new JSEncrypt();
encrypt.setPublicKey(publicKey);
// ajax请求发送的数据对象
var sendData = new Object();
// 将data数组赋给ajax对象
for ( var key in data) {
sendData[key]= encrypt.encrypt(data[key]);
}

$.ajax({
url: reqUrl,
type:'post' ,
data: sendData,
dataType:'json' ,
// contentType: 'application/json; charset=utf-8',
success: function (data) {
console.info(data);
},
error: function (xhr) {
// console.error('出错了');
}
});

}

// Call this code when the page is done loading.
$( function () {

$('#testme').click( function () {

var data = [];
data['username'] = $('#username' ).val();
data['passwd'] = $('#passwd' ).val();

var pkey = $('#pubkey' ).val();
encryptRequest('/WebForm2.aspx' , data, pkey);
});
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<label for="pubkey">Public Key</label><br />
<textarea id="pubkey" rows="15" cols="65">
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCDbrIgHK8qkz5IfK/A7At4SVZQ
31TalDPsc4vzeDVjd5ao46hcf+eOEQNm8jmxxHTm6WPSTy7RDVXG/NI489L9okkd
K++kVh2Z9GjBo5jw/n9EYojt8aYyEOc6cMHT2Fv+1smG+X/ W2HeXXoJJjcFLSjBe
CKx1SoCD4+ B2ZiDQ8wIDAQAB
</textarea><br />
<label for="input">Text to encrypt:</label><br />
name:<input id="username" name="username" type="text"></input><br />
password:<input id="passwd" name="passwd" type="password"></input><br />
<input id="testme" type="button" value="submit" /><br />
</div>
</form>
</body>
</html>

后端代码

解密

private RSACrypto rsaCrypto = new RSACrypto(PublicAttribute.PrivateKey, PublicAttribute.PublicKey);

// 获取参数
string usernameEncode = Request[ " username " ];
string pwdEncode = Request[ " pwd " ];

// 解密 RSA
string username = rsaCrypto.Decrypt(usernameEncode);
string pwd = rsaCrypto.Decrypt(pwdEncode);

类 RSACrypto

public class RSACrypto
{
private RSACryptoServiceProvider _privateKeyRsaProvider;
private RSACryptoServiceProvider _publicKeyRsaProvider;

public RSACrypto( string privateKey, string publicKey = null )
{
if (! string .IsNullOrEmpty(privateKey))
{
_privateKeyRsaProvider= CreateRsaProviderFromPrivateKey(privateKey);
}

if (! string .IsNullOrEmpty(publicKey))
{
_publicKeyRsaProvider= CreateRsaProviderFromPublicKey(publicKey);
}
}

public string Decrypt( string cipherText)
{
if (_privateKeyRsaProvider == null )
{
throw new Exception( " _privateKeyRsaProvider is null " );
}
return Encoding.UTF8.GetString(_privateKeyRsaProvider.Decrypt(System.Convert.FromBase64String(cipherText), false ));
}

public string Encrypt( string text)
{
if (_publicKeyRsaProvider == null )
{
throw new Exception( " _publicKeyRsaProvider is null " );
}
return Convert.ToBase64String(_publicKeyRsaProvider.Encrypt(Encoding.UTF8.GetBytes(text), false ));
}

private RSACryptoServiceProvider CreateRsaProviderFromPrivateKey( string privateKey)
{
var privateKeyBits = System.Convert.FromBase64String(privateKey);

var RSA = new RSACryptoServiceProvider();
var RSAparams = new RSAParameters();

using (BinaryReader binr = new BinaryReader( new MemoryStream(privateKeyBits)))
{
byte bt = 0 ;
ushort twobytes = 0 ;
twobytes= binr.ReadUInt16();
if (twobytes == 0x8130 )
binr.ReadByte();
else if (twobytes == 0x8230 )
binr.ReadInt16();
else
throw new Exception( " Unexpected value read binr.ReadUInt16() " );

twobytes= binr.ReadUInt16();
if (twobytes != 0x0102 )
throw new Exception( " Unexpected version " );

bt= binr.ReadByte();
if (bt != 0x00 )
throw new Exception( " Unexpected value read binr.ReadByte() " );

RSAparams.Modulus= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.Exponent= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.D= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.P= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.Q= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.DP= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.DQ= binr.ReadBytes(GetIntegerSize(binr));
RSAparams.InverseQ= binr.ReadBytes(GetIntegerSize(binr));
}

RSA.ImportParameters(RSAparams);
return RSA;
}

private int GetIntegerSize(BinaryReader binr)
{
byte bt = 0 ;
byte lowbyte = 0x00 ;
byte highbyte = 0x00 ;
int count = 0 ;
bt= binr.ReadByte();
if (bt != 0x02 )
return 0 ;
bt= binr.ReadByte();

if (bt == 0x81 )
count= binr.ReadByte();
else
if (bt == 0x82 )
{
highbyte= binr.ReadByte();
lowbyte= binr.ReadByte();
byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
count= BitConverter.ToInt32(modint, 0 );
}
else
{
count= bt;
}

while (binr.ReadByte() == 0x00 )
{
count-= 1 ;
}
binr.BaseStream.Seek(- 1 , SeekOrigin.Current);
return count;
}

private RSACryptoServiceProvider CreateRsaProviderFromPublicKey( string publicKeyString)
{
// encoded OID sequence for PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
byte [] x509key;
byte[] seq = new byte[ 15 ];
int x509size;

x509key= Convert.FromBase64String(publicKeyString);
x509size= x509key.Length;

// --------- Set up stream to read the asn.1 encoded SubjectPublicKeyInfo blob ------
using (MemoryStream mem = new MemoryStream(x509key))
{
using (BinaryReader binr = new BinaryReader(mem)) // wrap Memory Stream with BinaryReader for easy reading
{
byte bt = 0 ;
ushort twobytes = 0 ;

twobytes= binr.ReadUInt16();
if (twobytes == 0x8130) // data read as little endian order (actual data order for Sequence is 30 81)
binr.ReadByte(); // advance 1 byte
else if (twobytes == 0x8230 )
binr.ReadInt16(); // advance 2 bytes
else
return null ;

seq= binr.ReadBytes( 15); // read the Sequence OID
if (!CompareBytearrays(seq, SeqOID)) // make sure Sequence for OID is correct
return null ;

twobytes= binr.ReadUInt16();
if (twobytes == 0x8103) // data read as little endian order (actual data order for Bit String is 03 81)
binr.ReadByte(); // advance 1 byte
else if (twobytes == 0x8203 )
binr.ReadInt16(); // advance 2 bytes
else
return null ;

bt= binr.ReadByte();
if (bt != 0x00) // expect null byte next
return null ;

twobytes= binr.ReadUInt16();
if (twobytes == 0x8130) // data read as little endian order (actual data order for Sequence is 30 81)
binr.ReadByte(); // advance 1 byte
else if (twobytes == 0x8230 )
binr.ReadInt16(); // advance 2 bytes
else
return null ;

twobytes= binr.ReadUInt16();
byte lowbyte = 0x00 ;
byte highbyte = 0x00 ;

if (twobytes == 0x8102) // data read as little endian order (actual data order for Integer is 02 81)
lowbyte = binr.ReadByte(); // read next bytes which is bytes in modulus
else if (twobytes == 0x8202 )
{
highbyte= binr.ReadByte(); // advance 2 bytes
lowbyte = binr.ReadByte();
}
else
return null ;
byte[] modint = { lowbyte, highbyte, 0x00, 0x00 }; // reverse byte order since asn.1 key uses big endian order
int modsize = BitConverter.ToInt32(modint, 0 );

int firstbyte = binr.PeekChar();
if (firstbyte == 0x00 )
{ // if first byte (highest order) of modulus is zero, don't include it
binr.ReadByte(); // skip this null byte
modsize -= 1; // reduce modulus buffer size by 1
}

byte[] modulus = binr.ReadBytes(modsize); // read the modulus bytes

if (binr.ReadByte() != 0x02) // expect an Integer for the exponent data
return null ;
int expbytes = ( int)binr.ReadByte(); // should only need one byte for actual exponent data (for all useful values)
byte[] exponent = binr.ReadBytes(expbytes);

// ------- create RSACryptoServiceProvider instance and initialize with public key -----
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSAParameters RSAKeyInfo= new RSAParameters();
RSAKeyInfo.Modulus= modulus;
RSAKeyInfo.Exponent= exponent;
RSA.ImportParameters(RSAKeyInfo);

return RSA;
}

}
}

private bool CompareBytearrays( byte[] a, byte [] b)
{
if (a.Length != b.Length)
return false ;
int i = 0 ;
foreach ( byte c in a)
{
if (c != b[i])
return false ;
i++ ;
}
return true ;
}
}

到此结束了。