laiyuan:
概述
RSA被称为非对称性加密算法，意思就是加密和解密用的不是同一份密钥。RSA算法的密钥分为公钥和私钥，两者内容不同，用途也不同。公钥用于加密，一般交给客户端使用；私钥用于解密，一般由服务器管理。反过来，对称性加密算法，指的就是用同一份密钥进行加密解密了，比如DES加密算法。
RSA算法实现
一、生成密钥对
在使用RSA加密解密之前，首先要生成密钥对。RSA算法的密钥可以通过两个途径生成，一是借助openssl命令终端，二是使用代码生成。
1、Openssl生成密钥对
首先你得安装Openssl，这里就不再叙述如何安装Openssl了，正好给你个机会去撩一下度娘。
第一步，生成私钥。现在我们找到openssl安装目录的bin文件夹，双击打开openssl.exe，输入命令
[java] view plain copy
1. genrsa -out rsa_private_key.pem 1024
在openssl.exe的同级目录下可以找到生成的私钥文件rsa_private_key.pem，打开后看到的内容类似下面
[java] view plain copy
请忽略带有虚线的第一行和最后一行，中间的内容就是我们的私钥了。
1. -----BEGIN RSA PRIVATE KEY-----
2. MIICWwIBAAKBgQC7yil5BUsHf+PdPl9fzdr3FNyrXDPJwV8Vfk3hCsiqs3YzHYjE
3. YpHZiaF8dg9wB/aqmKRA0KFH2eTv++GNf0fAtdfbZUeq1Y79BDs23kSoS6g0Xe8m
4. D76A2oD+G0o/llsBjpmWViFaCre0uALyOwd412pU7yj+IJU+JlNlxLapNwIDAQAB
5. AoGAH0C+9DgwS3g6WQjXYJ9m8LYVH6PBrrMy+uXBWlGsIdSqOEmTCHQLJ/Qi3w7a
6. 9N8uayfqNitCnC2kT1hRKnZjX2Miy0LCfLsH6REV1NUgSmC7lr/TKkq9Hnvp1Y0H
7. bi7u5ux6QUzY8Yb7f6go7rAk764EikV8QeuRKsQP0jaPIckCQQDg8yyWlsWL298C
8. sn15tQAqmNI8kWpmOmZuvNE0oTzodsMCfi0K3e5c3KtHUgso1hPWTxJguRpWw1jS
9. 4NsoYWJTAkEA1bXlP1vHF4DW9XjoE/VSb3ReUXvqCx96IrdxcKXKOPrNsGOpKBkL
10. 3x74jImXjIiSEe4ePvOHsQ5HgB9scPlJDQJATcrKuKkbV+qJjN09F0HI9PI0gk2n
11. hgLcOZ+CmbjI33typQINgZyOOf72HIv63/xoj8x4hop82VRk+0hXgfdrkQJABQFo
12. qC4/IIbNAhzd2rHRR3kDSIdNeQs4sh1307qeXO1K6gm7iYvkoko4ahpC6XC9cxwP
13. q0vK7tO1ywNxZ8f+9QJAO2sXpLl4G/I0xrizv9Yoe7MON+8CsMXIUb0Swf3Q4Bbj
14. YNWXYD1BBa1qkIQU48dLgbJU24Abzl57nkSN/nns4A==
15. -----END RSA PRIVATE KEY-----第二步，生成公钥。继续在openssl终端窗口输入命令：
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1. rsa -in rsa_private_key.pem -out rsa_public_key.pem -pubout
这里根据私钥数据，生成了公钥，同样也是保存在openssl.exe同级目录下，打开看里面的内容：
[java] view plain copy
1. -----BEGIN PUBLIC KEY-----
2. MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC7yil5BUsHf+PdPl9fzdr3FNyr
3. XDPJwV8Vfk3hCsiqs3YzHYjEYpHZiaF8dg9wB/aqmKRA0KFH2eTv++GNf0fAtdfb
4. ZUeq1Y79BDs23kSoS6g0Xe8mD76A2oD+G0o/llsBjpmWViFaCre0uALyOwd412pU
5. 7yj+IJU+JlNlxLapNwIDAQAB
6. -----END PUBLIC KEY-----
到这里，密钥对基本生成了，但是这个密钥对的私钥无法在代码中直接使用，需要对私钥进行PKCS#8编码，继续敲命令：
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1. pkcs8 -topk8 -in rsa_private_key.pem -out pkcs8_rsa_private_key.pem -nocrypt
同样在openssl.exe同级目录下找到文件pkcs8_rsa_private_key.pem，这里就是我们最终需要的私钥了。
下面可以看到内容跟rsa_private_key.pem里面的内容是不一样的：
[java] view plain copy
1. -----BEGIN PRIVATE KEY-----
2. MIICdQIBADANBgkqhkiG9w0BAQEFAASCAl8wggJbAgEAAoGBALvKKXkFSwd/490+
3. X1/N2vcU3KtcM8nBXxV+TeEKyKqzdjMdiMRikdmJoXx2D3AH9qqYpEDQoUfZ5O/7
4. 4Y1/R8C119tlR6rVjv0EOzbeRKhLqDRd7yYPvoDagP4bSj+WWwGOmZZWIVoKt7S4
5. AvI7B3jXalTvKP4glT4mU2XEtqk3AgMBAAECgYAfQL70ODBLeDpZCNdgn2bwthUf
6. o8GuszL65cFaUawh1Ko4SZMIdAsn9CLfDtr03y5rJ+o2K0KcLaRPWFEqdmNfYyLL
7. QsJ8uwfpERXU1SBKYLuWv9MqSr0ee+nVjQduLu7m7HpBTNjxhvt/qCjusCTvrgSK
8. RXxB65EqxA/SNo8hyQJBAODzLJaWxYvb3wKyfXm1ACqY0jyRamY6Zm680TShPOh2
9. wwJ+LQrd7lzcq0dSCyjWE9ZPEmC5GlbDWNLg2yhhYlMCQQDVteU/W8cXgNb1eOgT
10. 9VJvdF5Re+oLH3oit3Fwpco4+s2wY6koGQvfHviMiZeMiJIR7h4+84exDkeAH2xw
11. +UkNAkBNysq4qRtX6omM3T0XQcj08jSCTaeGAtw5n4KZuMjfe3KlAg2BnI45/vYc
12. i/rf/GiPzHiGinzZVGT7SFeB92uRAkAFAWioLj8ghs0CHN3asdFHeQNIh015Cziy
13. HXfTup5c7UrqCbuJi+SiSjhqGkLpcL1zHA+rS8ru07XLA3Fnx/71AkA7axekuXgb
14. 8jTGuLO/1ih7sw437wKwxchRvRLB/dDgFuNg1ZdgPUEFrWqQhBTjx0uBslTbgBvO
15. XnueRI3+eezg
16. -----END PRIVATE KEY-----
2、代码生成密钥对
除了上面的openssl方法可以生成密钥对外，使用代码也是可以生成的，具体的代码如下：
[java] view plain copy
1. public static KeyPair generateRSAKeyPair(int keyLength)
2. {
3. try
4. {
5. KeyPairGenerator kpg = KeyPairGenerator.getInstance(RSA);
6. kpg.initialize(keyLength);
7. return kpg.genKeyPair();
8. catch (NoSuchAlgorithmException e)
9. {
10. e.printStackTrace();
11. return null;
12. }
13. }
keyLength范围512~2048，
一般取1024，其他值本人没尝试过，有探索精神的可以自行更改。
通过keyPair.getPublic().getEncoded()，keyPair.getPrivate().getEncoded()分别获取公钥、私钥的字节码。
为了更直观一点，可以通过Base64编码把字节码转为可读的字符串保存起来 Base64Utils.encode(rsaKeyPair.getPublic().getEncoded());
二、RSA加密解密代码实现
废话少说，赶着回家吃饭，上代码：
[java] view plain copy
1. package com.yspay.sdk.util;
2.
3. import java.io.BufferedReader;
4. import java.io.ByteArrayOutputStream;
5. import java.io.IOException;
6. import java.io.InputStream;
7. import java.io.InputStreamReader;
8. import java.math.BigInteger;
9. import java.security.KeyFactory;
10. import java.security.KeyPair;
11. import java.security.KeyPairGenerator;
12. import java.security.NoSuchAlgorithmException;
13. import java.security.PrivateKey;
14. import java.security.PublicKey;
15. import java.security.interfaces.RSAPrivateKey;
16. import java.security.interfaces.RSAPublicKey;
17. import java.security.spec.InvalidKeySpecException;
18. import java.security.spec.PKCS8EncodedKeySpec;
19. import java.security.spec.RSAPublicKeySpec;
20. import java.security.spec.X509EncodedKeySpec;
21.
22. import javax.crypto.Cipher;
23.
24. /**
25. *
26. */
27. public final class RSAUtils
28. {
29. private static String RSA = "RSA";
30.
31. /**
32. * 随机生成RSA密钥对(默认密钥长度为1024)
33. *
34. * @return
35. */
36. public static KeyPair generateRSAKeyPair()
37. {
38. return generateRSAKeyPair(1024);
39. }
40.
41. /**
42. * 随机生成RSA密钥对
43. *
44. * @param keyLength
45. * 密钥长度，范围：512～2048<br>
46. * 一般1024
47. * @return
48. */
49. public static KeyPair generateRSAKeyPair(int keyLength)
50. {
51. try
52. {
53. KeyPairGenerator kpg = KeyPairGenerator.getInstance(RSA);
54. kpg.initialize(keyLength);
55. return kpg.genKeyPair();
56. catch (NoSuchAlgorithmException e)
57. {
58. e.printStackTrace();
59. return null;
60. }
61. }
62.
63. /**
64. * 用公钥加密 <br>
65. * 每次加密的字节数，不能超过密钥的长度值除以 8 再减去 11，所以采取分段加密的方式规避
66. *
67. * @param data 需加密数据的byte数据
68. * @param publicKey 公钥
69. * @return 加密后的byte型数据
70. */
71. public static byte[] encryptData(byte[] data, PublicKey publicKey)
72. {
73. try
74. {
75. Cipher cipher = Cipher.getInstance(RSA);
76. // 编码前设定编码方式及密钥
77. cipher.init(Cipher.ENCRYPT_MODE, publicKey);
78.
79. RSAPublicKey rsaPublicKey = (RSAPublicKey) publicKey;
80. // 模长
81. int keyLen = rsaPublicKey.getModulus().bitLength() / 8;
82. int maxEncryptBlock = keyLen - 11;
83.
84. //如果明文长度大于模长-11则要分组加密
85. int inputLen = data.length;
86. new ByteArrayOutputStream();
87. int offSet = 0;
88. byte[] temp;
89. int i = 0;
90. // 对数据分段加密
91. while (inputLen - offSet > 0) {
92. if (inputLen - offSet > maxEncryptBlock) {
93. temp = cipher.doFinal(data, offSet, maxEncryptBlock);
94. else {
95. temp = cipher.doFinal(data, offSet, inputLen - offSet);
96. }
97. 0, temp.length);
98. i++;
99. offSet = i * maxEncryptBlock;
100. }
101. byte[] encryptedData = out.toByteArray();
102. out.close();
103. // 传入编码数据并返回编码结果
104. return encryptedData;
105. catch (Exception e)
106. {
107. e.printStackTrace();
108. return null;
109. }
110. }
111.
112. /**
113. * 用私钥解密
114. *
115. * @param encryptedData 经过encryptedData()加密返回的byte数据
116. * @param privateKey 私钥
117. * @return
118. */
119. public static byte[] decryptData(byte[] encryptedData, PrivateKey privateKey)
120. {
121. try
122. {
123. Cipher cipher = Cipher.getInstance(RSA);
124. cipher.init(Cipher.DECRYPT_MODE, privateKey);
125.
126. RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) privateKey;
127. // 模长
128. int keyLen = rsaPrivateKey.getModulus().bitLength() / 8;
129. int maxDecryptBlock = keyLen;//不用减11
130.
131. //如果密文长度大于模长则要分组解密
132. int inputLen = encryptedData.length;
133. new ByteArrayOutputStream();
134. int offSet = 0;
135. byte[] temp;
136. int i = 0;
137. // 对数据分段解密
138. while (inputLen - offSet > 0) {
139. if (inputLen - offSet > maxDecryptBlock) {
140. temp = cipher.doFinal(encryptedData, offSet, maxDecryptBlock);
141. else {
142. temp = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
143. }
144. 0, temp.length);
145. i++;
146. offSet = i * maxDecryptBlock;
147. }
148. byte[] decryptedData = out.toByteArray();
149. out.close();
150.
151. return decryptedData;
152. catch (Exception e)
153. {
154. e.printStackTrace();
155. return null;
156. }
157. }
158.
159. /**
160. * 通过公钥byte[](publicKey.getEncoded())将公钥还原，适用于RSA算法
161. *
162. * @param keyBytes
163. * @return
164. * @throws NoSuchAlgorithmException
165. * @throws InvalidKeySpecException
166. */
167. public static PublicKey getPublicKey(byte[] keyBytes) throws NoSuchAlgorithmException,
168. InvalidKeySpecException
169. {
170. new X509EncodedKeySpec(keyBytes);
171. KeyFactory keyFactory = KeyFactory.getInstance(RSA);
172. PublicKey publicKey = keyFactory.generatePublic(keySpec);
173. return publicKey;
174. }
175.
176. /**
177. * 通过私钥byte[]将公钥还原，适用于RSA算法
178. *
179. * @param keyBytes
180. * @return
181. * @throws NoSuchAlgorithmException
182. * @throws InvalidKeySpecException
183. */
184. public static PrivateKey getPrivateKey(byte[] keyBytes) throws NoSuchAlgorithmException,
185. InvalidKeySpecException
186. {
187. new PKCS8EncodedKeySpec(keyBytes);
188. KeyFactory keyFactory = KeyFactory.getInstance(RSA);
189. PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
190. return privateKey;
191. }
192.
193. /**
194. * 使用N、e值还原公钥
195. *
196. * @param modulus
197. * @param publicExponent
198. * @return
199. * @throws NoSuchAlgorithmException
200. * @throws InvalidKeySpecException
201. */
202. public static PublicKey getPublicKey(String modulus, String publicExponent)
203. throws NoSuchAlgorithmException, InvalidKeySpecException
204. {
205. new BigInteger(modulus);
206. new BigInteger(publicExponent);
207. new RSAPublicKeySpec(bigIntModulus, bigIntPrivateExponent);
208. KeyFactory keyFactory = KeyFactory.getInstance(RSA);
209. PublicKey publicKey = keyFactory.generatePublic(keySpec);
210. return publicKey;
211. }
212.
213. /**
214. * 使用N、d值还原私钥
215. *
216. * @param modulus
217. * @param privateExponent
218. * @return
219. * @throws NoSuchAlgorithmException
220. * @throws InvalidKeySpecException
221. */
222. public static PrivateKey getPrivateKey(String modulus, String privateExponent)
223. throws NoSuchAlgorithmException, InvalidKeySpecException
224. {
225. new BigInteger(modulus);
226. new BigInteger(privateExponent);
227. new RSAPublicKeySpec(bigIntModulus, bigIntPrivateExponent);
228. KeyFactory keyFactory = KeyFactory.getInstance(RSA);
229. PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
230. return privateKey;
231. }
232.
233. /**
234. * 从字符串中加载公钥
235. *
236. * @param publicKeyStr
237. * 公钥数据字符串
238. * @throws Exception
239. * 加载公钥时产生的异常
240. */
241. public static PublicKey loadPublicKey(String publicKeyStr) throws Exception
242. {
243. try
244. {
245. byte[] buffer = Base64Utils.decode(publicKeyStr);
246. KeyFactory keyFactory = KeyFactory.getInstance(RSA);
247. new X509EncodedKeySpec(buffer);
248. return (RSAPublicKey) keyFactory.generatePublic(keySpec);
249. catch (NoSuchAlgorithmException e)
250. {
251. throw new Exception("无此算法");
252. catch (InvalidKeySpecException e)
253. {
254. throw new Exception("公钥非法");
255. catch (NullPointerException e)
256. {
257. throw new Exception("公钥数据为空");
258. }
259. }
260.
261. /**
262. * 从字符串中加载私钥<br>
263. * 加载时使用的是PKCS8EncodedKeySpec（PKCS#8编码的Key指令）。
264. *
265. * @param privateKeyStr
266. * @return
267. * @throws Exception
268. */
269. public static PrivateKey loadPrivateKey(String privateKeyStr) throws Exception
270. {
271. try
272. {
273. byte[] buffer = Base64Utils.decode(privateKeyStr);
274. //X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
275. new PKCS8EncodedKeySpec(buffer);
276. KeyFactory keyFactory = KeyFactory.getInstance(RSA);
277. return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
278. catch (NoSuchAlgorithmException e)
279. {
280. throw new Exception("无此算法");
281. catch (InvalidKeySpecException e)
282. {
283. throw new Exception("私钥非法");
284. catch (NullPointerException e)
285. {
286. throw new Exception("私钥数据为空");
287. }
288. }
289.
290. /**
291. * 从文件中输入流中加载公钥
292. *
293. * @param in
294. * 公钥输入流
295. * @throws Exception
296. * 加载公钥时产生的异常
297. */
298. public static PublicKey loadPublicKey(InputStream in) throws Exception
299. {
300. try
301. {
302. return loadPublicKey(readKey(in));
303. catch (IOException e)
304. {
305. throw new Exception("公钥数据流读取错误");
306. catch (NullPointerException e)
307. {
308. throw new Exception("公钥输入流为空");
309. }
310. }
311.
312. /**
313. * 从文件中加载私钥
314. * @param in
315. * @return 私钥
316. * @throws Exception
317. */
318. public static PrivateKey loadPrivateKey(InputStream in) throws Exception
319. {
320. try
321. {
322. return loadPrivateKey(readKey(in));
323. catch (IOException e)
324. {
325. throw new Exception("私钥数据读取错误");
326. catch (NullPointerException e)
327. {
328. throw new Exception("私钥输入流为空");
329. }
330. }
331.
332. /**
333. * 读取密钥信息
334. *
335. * @param in
336. * @return
337. * @throws IOException
338. */
339. private static String readKey(InputStream in) throws IOException
340. {
341. new BufferedReader(new InputStreamReader(in));
342. null;
343. new StringBuilder();
344. while ((readLine = br.readLine()) != null)
345. {
346. if (readLine.charAt(0) == '-')
347. {
348. continue;
349. else
350. {
351. sb.append(readLine);
352. '\r');
353. }
354. }
355.
356. return sb.toString();
357. }
358.
359. }Base64编码工具可以使用系统自带的android.util.Base64，也可以自己实现，以下是 从别处扣来的代码：
[java] view plain copy
1. package com.yspay.sdk.util;
2.
3. import java.io.UnsupportedEncodingException;
4.
5. /**
6. * Created by MPC on 2017/5/24.
7. */
8.
9. public class Base64Utils {
10.
11. private static char[] base64EncodeChars = new char[]
12. 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
13. 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
14. 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',
15. '6', '7', '8', '9', '+', '/' };
16. private static byte[] base64DecodeChars = new byte[]
17. 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
18. 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53,
19. 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
20. 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29,
21. 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1,
22. 1, -1, -1 };
23.
24. /**
25. * 加密
26. *
27. * @param data
28. * @return
29. */
30. public static String encode(byte[] data)
31. {
32. new StringBuffer();
33. int len = data.length;
34. int i = 0;
35. int b1, b2, b3;
36. while (i < len)
37. {
38. 0xff;
39. if (i == len)
40. {
41. 2]);
42. 0x3) << 4]);
43. "==");
44. break;
45. }
46. 0xff;
47. if (i == len)
48. {
49. 2]);
50. 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
51. 0x0f) << 2]);
52. "=");
53. break;
54. }
55. 0xff;
56. 2]);
57. 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
58. 0x0f) << 2) | ((b3 & 0xc0) >>> 6)]);
59. 0x3f]);
60. }
61. return sb.toString();
62. }
63.
64. /**
65. * 解密
66. *
67. * @param str
68. * @return
69. */
70. public static byte[] decode(String str)
71. {
72. try
73. {
74. return decodePrivate(str);
75. catch (UnsupportedEncodingException e)
76. {
77. e.printStackTrace();
78. }
79. return new byte[]
80. {};
81. }
82.
83. private static byte[] decodePrivate(String str) throws UnsupportedEncodingException
84. {
85. new StringBuffer();
86. byte[] data = null;
87. "US-ASCII");
88. int len = data.length;
89. int i = 0;
90. int b1, b2, b3, b4;
91. while (i < len)
92. {
93.
94. do
95. {
96. b1 = base64DecodeChars[data[i++]];
97. while (i < len && b1 == -1);
98. if (b1 == -1)
99. break;
100.
101. do
102. {
103. b2 = base64DecodeChars[data[i++]];
104. while (i < len && b2 == -1);
105. if (b2 == -1)
106. break;
107. char) ((b1 << 2) | ((b2 & 0x30) >>> 4)));
108.
109. do
110. {
111. b3 = data[i++];
112. if (b3 == 61)
113. return sb.toString().getBytes("iso8859-1");
114. b3 = base64DecodeChars[b3];
115. while (i < len && b3 == -1);
116. if (b3 == -1)
117. break;
118. char) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));
119.
120. do
121. {
122. b4 = data[i++];
123. if (b4 == 61)
124. return sb.toString().getBytes("iso8859-1");
125. b4 = base64DecodeChars[b4];
126. while (i < len && b4 == -1);
127. if (b4 == -1)
128. break;
129. char) (((b3 & 0x03) << 6) | b4));
130. }
131. return sb.toString().getBytes("iso8859-1");
public static void main(String[] args) {
RSAPublicKey publicKey = RSAUtils.getDefaultPublicKey();
String modulus = new String(Hex.encodeHex(publicKey.getModulus().toByteArray()));
String exponent = new String(Hex.encodeHex(publicKey.getPublicExponent().toByteArray()));
System.out.println("modulus:"+modulus);
System.out.println("exponent:"+exponent);
String plaintext = "111111";
String encrypttext = encryptString(plaintext);
System.out.println(encrypttext);
String decrypttext = decryptString(encrypttext);
System.out.println(decrypttext);
}
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