最近做手機項目，服務器端使用的是php，客戶端分別有android版及ios版，在部分通訊環節需要對內容進行加密，RSA加密演算法是一種非對稱加密演算法，能夠較好達到要求，不過如果服務器架設https服務，較為麻煩，系統效率也不高，我們只需要在部分重要接口上使用RSA加密解密就行。首先，準備工作

openssl genrsa -out rsa_PRivate_key.pem 1024openssl pkcs8 -topk8 -inform PEM -in rsa_private_key.pem -outform PEM -nocrypt -out private_key.pemopenssl rsa -in rsa_private_key.pem -pubout -out rsa_public_key.pem
第一條命令生成原始 RSA私鑰文件 rsa_private_key.pem，第二條命令將原始 RSA私鑰轉換為 pkcs8格式，第三條生成RSA公鑰 rsa_public_key.pem從上面看出通過私鑰能生成對應的公鑰，因此我們將私鑰private_key.pem用在服務器端，公鑰發放給android跟ios等前端
第二步，php服務器端，使用openssl方法來進行加密解密類，代碼如下：
<?php/** * @author alun (http://alunblog.duapp.com) * @version 1.0 * @created 2013-5-17 */ class Rsa{private static $PRIVATE_KEY = '-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----';    /**    *返回對應的私鑰    */    private static function getPrivateKey(){            $privKey = self::$PRIVATE_KEY;                 return openssl_pkey_get_private($privKey);          }     /**     * 私鑰加密     */    public static function privEncrypt($data)    {        if(!is_string($data)){                return null;        }                   return openssl_private_encrypt($data,$encrypted,self::getPrivateKey())? base64_encode($encrypted) : null;    }            /**     * 私鑰解密     */    public static function privDecrypt($encrypted)    {        if(!is_string($encrypted)){                return null;        }        return (openssl_private_decrypt(base64_decode($encrypted), $decrypted, self::getPrivateKey()))? $decrypted : null;    }} ?>
打開private_key.pem，將上面的$PRIVATE_KEY，替換成private_key.pem的內容即可，服務器端我們只需要使用私鑰來加密解密。
第三步，android前端，使用java的Cipher類來實現加密解密類，代碼如下：
import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.InputStream;import java.security.KeyFactory;import java.security.NoSuchAlgorithmException;import java.security.PublicKey;import java.security.spec.X509EncodedKeySpec;import javax.crypto.Cipher; import android.util.Base64; /** * @author alun (http://alunblog.duapp.com) * @version 1.0 * @created 2013-5-17 */public class Rsa {    private static final String RSA_PUBLICE =            "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPZ1Ju6zzYUoL7HYzLgneROyDC" + "/r" +            "Qf/NANWGO42FfXwQinYVSpqnmtukGLsOhVuwdNH6aRFE0ms3bkpp/WL4cfVDgnCO" + "/r" +            "+W9J6vRVpuTuD/iqfJd9TNacLCd3Jvg3HhjqxbJeO74fYnYqo/mmyJSeLE5iZg4I" + "/r" +            "Zm5LPWBZWUp3ULCAZQIDAQAB";    private static final String ALGORITHM = "RSA";     /**     * 得到公鑰     * @param algorithm     * @param bysKey     * @return     */    private static PublicKey getPublicKeyFromX509(String algorithm,            String bysKey) throws NoSuchAlgorithmException, Exception {        byte[] decodedKey = Base64.decode(bysKey,Base64.DEFAULT);        X509EncodedKeySpec x509 = new X509EncodedKeySpec(decodedKey);         KeyFactory keyFactory = KeyFactory.getInstance(algorithm);        return keyFactory.generatePublic(x509);    }     /**     * 使用公鑰加密     * @param content     * @param key     * @return     */    public static String encryptByPublic(String content) {        try {            PublicKey pubkey = getPublicKeyFromX509(ALGORITHM, RSA_PUBLICE);             Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");            cipher.init(Cipher.ENCRYPT_MODE, pubkey);             byte plaintext[] = content.getBytes("UTF-8");            byte[] output = cipher.doFinal(plaintext);             String s = new String(Base64.encode(output,Base64.DEFAULT));             return s;         } catch (Exception e) {            return null;        }    }     /**    * 使用公鑰解密    * @param content 密文    * @param key 商戶私鑰    * @return 解密后的字符串    */    public static String decryptByPublic(String content) {        try {            PublicKey pubkey = getPublicKeyFromX509(ALGORITHM, RSA_PUBLICE);            Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");            cipher.init(Cipher.DECRYPT_MODE, pubkey);            InputStream ins = new ByteArrayInputStream(Base64.decode(content,Base64.DEFAULT));            ByteArrayOutputStream writer = new ByteArrayOutputStream();            byte[] buf = new byte[128];            int bufl;            while ((bufl = ins.read(buf)) != -1) {                byte[] block = null;                if (buf.length == bufl) {                block = buf;                } else {                block = new byte[bufl];                for (int i = 0; i < bufl; i++) {                    block[i] = buf[i];                }                }                writer.write(cipher.doFinal(block));            }            return new String(writer.toByteArray(), "utf-8");        } catch (Exception e) {            return null;        }    } }
需要注意的是，在初始化Cipher對象時，一定要指明使用"RSA/ECB/PKCS1Padding"格式如Cipher.getInstance("RSA/ECB/PKCS1Padding");打開rsa_public_key.pem文件，將上面代碼的RSA_PUBLICE替換成其中內容即可。
第四步，ios前端，iOS上沒有直接處理RSA加密的API，網上說的大多數也是處理X.509的證書的方法來實現，不過X.509證書是帶簽名的，在php端openssl_pkey_get_private方法獲取密鑰時，第二個參數需要傳簽名，而android端實現X.509證書加密解密較為不易，在這里我們利用ios兼容c程序的特點，利用openssl的api實現rsa的加密解密，代碼如下：CRSA.h代碼：
#import <Foundation/Foundation.h>#include <openssl/rsa.h>#include <openssl/pem.h>#include <openssl/err.h> typedef enum {    KeyTypePublic,    KeyTypePrivate}KeyType; typedef enum {    RSA_PADDING_TYPE_NONE       = RSA_NO_PADDING,    RSA_PADDING_TYPE_PKCS1      = RSA_PKCS1_PADDING,    RSA_PADDING_TYPE_SSLV23     = RSA_SSLV23_PADDING}RSA_PADDING_TYPE; @interface CRSA : NSObject{    RSA *_rsa;}+ (id)shareInstance;- (BOOL)importRSAKeyWithType:(KeyType)type;- (int)getBlockSizeWithRSA_PADDING_TYPE:(RSA_PADDING_TYPE)padding_type;- (NSString *) encryptByRsa:(NSString*)content withKeyType:(KeyType)keyType;- (NSString *) decryptByRsa:(NSString*)content withKeyType:(KeyType)keyType;@end
CRSA.m代碼
#import "CRSA.h" #define BUFFSIZE  1024#import "Base64.h" #define PADDING RSA_PADDING_TYPE_PKCS1@implementation CRSA + (id)shareInstance{    static CRSA *_crsa = nil;    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        _crsa = [[self alloc] init];    });    return _crsa;}- (BOOL)importRSAKeyWithType:(KeyType)type{    FILE *file;    NSString *keyName = type == KeyTypePublic ? @"public_key" : @"private_key";    NSString *keyPath = [[NSBundle mainBundle] pathForResource:keyName ofType:@"pem"];         file = fopen([keyPath UTF8String], "rb");         if (NULL != file)    {        if (type == KeyTypePublic)        {            _rsa = PEM_read_RSA_PUBKEY(file, NULL, NULL, NULL);            assert(_rsa != NULL);        }        else        {            _rsa = PEM_read_RSAPrivateKey(file, NULL, NULL, NULL);            assert(_rsa != NULL);        }                 fclose(file);                 return (_rsa != NULL) ? YES : NO;    }         return NO;} - (NSString *) encryptByRsa:(NSString*)content withKeyType:(KeyType)keyType{    if (![self importRSAKeyWithType:keyType])         return nil;         int status;    int length  = [content length];    unsigned char input[length + 1];    bzero(input, length + 1);    int i = 0;    for (; i < length; i++)    {        input[i] = [content characterAtIndex:i];    }         NSInteger  flen = [self getBlockSizeWithRSA_PADDING_TYPE:PADDING];         char *encData = (char*)malloc(flen);    bzero(encData, flen);         switch (keyType) {        case KeyTypePublic:            status = RSA_public_encrypt(length, (unsigned char*)input, (unsigned char*)encData, _rsa, PADDING);            break;                     default:            status = RSA_private_encrypt(length, (unsigned char*)input, (unsigned char*)encData, _rsa, PADDING);            break;    }         if (status)    {        NSData *returnData = [NSData dataWithBytes:encData length:status];        free(encData);        encData = NULL;                 NSString *ret = [returnData base64EncodedString];        return ret;    }         free(encData);    encData = NULL;         return nil;} - (NSString *) decryptByRsa:(NSString*)content withKeyType:(KeyType)keyType{    if (![self importRSAKeyWithType:keyType])        return nil;         int status;     NSData *data = [content base64DecodedData];    int length = [data length];         NSInteger flen = [self getBlockSizeWithRSA_PADDING_TYPE:PADDING];    char *decData = (char*)malloc(flen);    bzero(decData, flen);         switch (keyType) {        case KeyTypePublic:            status = RSA_public_decrypt(length, (unsigned char*)[data bytes], (unsigned char*)decData, _rsa, PADDING);            break;                     default:            status = RSA_private_decrypt(length, (unsigned char*)[data bytes], (unsigned char*)decData, _rsa, PADDING);            break;    }         if (status)    {        NSMutableString *decryptString = [[NSMutableString alloc] initWithBytes:decData length:strlen(decData) encoding:NSASCIIStringEncoding];        free(decData);        decData = NULL;                 return decryptString;    }         free(decData);    decData = NULL;         return nil;} - (int)getBlockSizeWithRSA_PADDING_TYPE:(RSA_PADDING_TYPE)padding_type{    int len = RSA_size(_rsa);         if (padding_type == RSA_PADDING_TYPE_PKCS1 || padding_type == RSA_PADDING_TYPE_SSLV23) {        len -= 11;    }         return len;}@end
其中openssl api包，我們可以在第一步RSA密鑰生成工具openssl的include文件夾中得到