RSA 分段加解密【解決“不正确的長度”的異常】
RSA 是常用的非對稱加密算法。最近使用時卻出現了“不正确的長度”的異常，研究發現是由于待加密的資料超長所緻。
.NET Framework 中提供的 RSA 算法規定：
待加密的位元組數不能超過密鑰的長度值除以 8 再減去 11（即：RSACryptoServiceProvider.KeySize / 8 - 11），而加密後得到密文的位元組數，正好是密鑰的長度值除以 8（即：RSACryptoServiceProvider.KeySize / 8）。
是以，如果要加密較長的資料，則可以采用分段加解密的方式，實作方式如下：
1 namespace Macroresolute.RSACryptoService
2 {
3 public static class RSACrypto
4 {
5 private static readonly Encoding Encoder = Encoding.UTF8;
6
7 public static String Encrypt(this String plaintext)
8 {
9 X509Certificate2 _X509Certificate2 = RSACrypto.RetrieveX509Certificate();
10 using (RSACryptoServiceProvider RSACryptography = _X509Certificate2.PublicKey.Key as RSACryptoServiceProvider)
11 {
12 Byte[] PlaintextData = RSACrypto.Encoder.GetBytes(plaintext);
13 int MaxBlockSize = RSACryptography.KeySize / 8 - 11; //加密塊最大長度限制
14
15 if (PlaintextData.Length <= MaxBlockSize)
16 return Convert.ToBase64String(RSACryptography.Encrypt(PlaintextData, false));
17
18 using (MemoryStream PlaiStream = new MemoryStream(PlaintextData))
19 using (MemoryStream CrypStream = new MemoryStream())
20 {
21 Byte[] Buffer = new Byte[MaxBlockSize];
22 int BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
23
24 while (BlockSize > 0)
25 {
26 Byte[] ToEncrypt = new Byte[BlockSize];
27 Array.Copy(Buffer, 0, ToEncrypt, 0, BlockSize);
28
29 Byte[] Cryptograph = RSACryptography.Encrypt(ToEncrypt, false);
30 CrypStream.Write(Cryptograph, 0, Cryptograph.Length);
31
32 BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
33 }
34
35 return Convert.ToBase64String(CrypStream.ToArray(), Base64FormattingOptions.None);
36 }
37 }
38 }
39
40 public static String Decrypt(this String ciphertext)
41 {
42 X509Certificate2 _X509Certificate2 = RSACrypto.RetrieveX509Certificate();
43 using (RSACryptoServiceProvider RSACryptography = _X509Certificate2.PrivateKey as RSACryptoServiceProvider)
44 {
45 Byte[] CiphertextData = Convert.FromBase64String(ciphertext);
46 int MaxBlockSize = RSACryptography.KeySize / 8; //解密塊最大長度限制
47
48 if (CiphertextData.Length <= MaxBlockSize)
49 return RSACrypto.Encoder.GetString(RSACryptography.Decrypt(CiphertextData, false));
50
51 using (MemoryStream CrypStream = new MemoryStream(CiphertextData))
52 using (MemoryStream PlaiStream = new MemoryStream())
53 {
54 Byte[] Buffer = new Byte[MaxBlockSize];
55 int BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
56
57 while (BlockSize > 0)
58 {
59 Byte[] ToDecrypt = new Byte[BlockSize];
60 Array.Copy(Buffer, 0, ToDecrypt, 0, BlockSize);
61
62 Byte[] Plaintext = RSACryptography.Decrypt(ToDecrypt, false);
63 PlaiStream.Write(Plaintext, 0, Plaintext.Length);
64
65 BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
66 }
67
68 return RSACrypto.Encoder.GetString(PlaiStream.ToArray());
69 }
70 }
71 }
72
73 private static X509Certificate2 RetrieveX509Certificate()
74 {
75 return null; //檢索用于 RSA 加密的 X509Certificate2 證書
76 }
77 }
78 } 注：以上加密方法傳回的字元串類型為原始的 Base-64 ，若要用于 URL 傳輸，需另行處理！
以上文章轉載自
http://www.cnblogs.com/zys529/archive/2012/05/24/2516539.html下面是自己修改
如果沒有證書請用以下方法
1 /// <summary>
2 ///
3 /// </summary>
4 public class RSADecryptEncrypt
5 {
6
7
8 private static readonly Encoding Encoder = Encoding.UTF8;
9 /// <summary>
10 /// 公鑰加密
11 /// </summary>
12 /// <param name="xmlPublicKey">公鑰</param>
13 /// <param name="EncryptString">加密字元串</param>
14 /// <returns></returns>
15 public static String Encrypt(string xmlPublicKey, string EncryptString)
16 {
17 using (RSACryptoServiceProvider RSACryptography = new RSACryptoServiceProvider())
18 {
19
20 RSACryptography.FromXmlString(xmlPublicKey);
21 Byte[] PlaintextData = RSADecryptEncrypt.Encoder.GetBytes(EncryptString);
22 int MaxBlockSize = RSACryptography.KeySize / 8 - 11;//加密塊最大長度限制
23
24 if (PlaintextData.Length <= MaxBlockSize)
25 return Convert.ToBase64String(RSACryptography.Encrypt(PlaintextData, false));
26
27 using (MemoryStream PlaiStream = new MemoryStream(PlaintextData))
28 using (MemoryStream CrypStream = new MemoryStream())
29 {
30 Byte[] Buffer = new Byte[MaxBlockSize];
31 int BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
32
33 while (BlockSize > 0)
34 {
35 Byte[] ToEncrypt = new Byte[BlockSize];
36 Array.Copy(Buffer, 0, ToEncrypt, 0, BlockSize);
37
38 Byte[] Cryptograph = RSACryptography.Encrypt(ToEncrypt, false);
39 CrypStream.Write(Cryptograph, 0, Cryptograph.Length);
40
41 BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
42 }
43
44 return Convert.ToBase64String(CrypStream.ToArray(), Base64FormattingOptions.None);
45 }
46 }
47 }
48
49 /// <summary>
50 /// 解密
51 /// </summary>
52 /// <param name="xmlPublicKey"></param>
53 /// <param name="EncryptString"></param>
54 /// <returns></returns>
55 public static String Decrypt(string xmlPrivateKey, string EncryptString)
56 {
57 using (RSACryptoServiceProvider RSACryptography = new RSACryptoServiceProvider())
58 {
59 RSACryptography.FromXmlString(xmlPrivateKey);
60 Byte[] CiphertextData = Convert.FromBase64String(EncryptString);
61 int MaxBlockSize = RSACryptography.KeySize / 8; //解密塊最大長度限制
62
63 if (CiphertextData.Length <= MaxBlockSize)
64 return RSADecryptEncrypt.Encoder.GetString(RSACryptography.Decrypt(CiphertextData, false));
65
66 using (MemoryStream CrypStream = new MemoryStream(CiphertextData))
67 using (MemoryStream PlaiStream = new MemoryStream())
68 {
69 Byte[] Buffer = new Byte[MaxBlockSize];
70 int BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
71
72 while (BlockSize > 0)
73 {
74 Byte[] ToDecrypt = new Byte[BlockSize];
75 Array.Copy(Buffer, 0, ToDecrypt, 0, BlockSize);
76
77 Byte[] Plaintext = RSACryptography.Decrypt(ToDecrypt, false);
78 PlaiStream.Write(Plaintext, 0, Plaintext.Length);
79
80 BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
81 }
82
83 return RSADecryptEncrypt.Encoder.GetString(PlaiStream.ToArray());
84 }
85 }
86 }
87
88
89 } ![Unity遊戲開發背景知識[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)