在前面的文章中我有说过AES和RSA这两种加密方式，正好在前段时间再项目中有使用到，在这里再把这两种加密方式综合在一起写一下，具体到他们的使用，以及RSA各种加密文件的生成。

 

一： RSA各种加密相关文件生成

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1、首先生成私钥（1024）

$ openssl genrsa -out private_key.pem 1024

    上面是生成了一个名为 private_key 的pem文件，也就是我们的私钥文件，他其实就是一个简单的txt文本文件而已。

 

2、生成证书请求文件

$ openssl req -new -key private_key.pem -out rsacert.csr

     上面命令中的 private_key.pem 就是我们的私钥文件，你会根据它生成一份名为 rsacert 的 csr 文件，当然这个名字是由你定义的。回车之后他会提示你输入国家、省份、mail等信息，当然你也可以什么都不填全部回车。大致是下面图的信息：

 

      通过上面的命令你有了一份 rsacert.csr 文件。

 

3、生成证书并且签名，我们设置有效期为10年，当然这个时间也是你自己定义的

$ openssl x509 -req -days 3650 -in rsacert.csr -signkey private_key.pem -out rsacert.crt

 

4、生成iOS要是用的公钥文件，文件格式为der格式，文件为 public_key.der （名字自己定义）

$ openssl x509 -outform der -in rsacert.crt -out public_key.der

 

5、生成iOS要使用的私钥，为p12格式（名字写了p.p12 这个自己定义）

$ openssl pkcs12 -export -out p.p12 -inkey private_key.pem -in rsacert.crt

       这里我们需要自己注意的点：这一步会提示给私钥文件设置密码，直接输入想要设置密码即可，然后敲回车，然后再验证刚才设置的密码，再次输入密码，然后敲回车，就可以验证了，设置密码是因为在解密时，private_key.p12文件需要和这里设置的密码配合使用，因此需要牢记此密码。具体的使用砸下面的代码中我们会展示出来怎么使用。

 

6、要是单单的iOS加密所需要的文件我们在这里也就已经设置OK了，但安卓一般在使用公钥的使用会用pem格式的公钥，所以这里我们还是需要再处理一下，在前面我们生成的公钥是der格式的，我们在生成一份pem格式的：

$ openssl rsa -in private_key.pem -out rsa_public_key.pem -pubout

 

7、安卓或者Java的同学肯定也需要私钥验证配合我们退耳机数据的，但他们需要的私钥都是PKCS8格式的，  所以我们还需要把我们pem格式的私钥转成PKCS8格式的：

$ openssl pkcs8 -topk8 -in private_key.pem -out pkcs8_private_key.pem -nocrypt

 

      通过上面的这么多步，我们需要的各种格式的文件我们就都创建完成了。大概如下图所示：

 

 

二：准备完成、解释一下为什么要配合使用

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      说说为什么要他们配合使用：

      要是我们单纯的使用AES，AES都知道是对称性加密，对称性的意思就是说加密和解密用的是同一个KEY，当我们移动端把数据加密完的时候我们把数据传给后端，这时候后端要想解开这个加密的数据就需要知道你是用什么KEY加密的，这时候可能有同学会想，那我们和后端定义相同的KEY不就OK了吗，嗯....那后端的KEY就保存在哎服务器，移动端的呢？写在本地还是去服务端请求？都不可以。因为用过这两种方式那安全性就没办法保证了。你写在本地的可以反编译你的代码，要是去服务端请求那就能被人劫持，只要知道了这个KEY那你的加密就变得毫无意义！但至少我们知道了一点，这个KEY很重要！

      很重要那我们该怎么处理呢，这时候就回到我们前面说的正题，AES和RSA配合使用，这个KEY的安全性就通过我们的RSA非对对称性加密保证，对称性就是加密解密要使用同一个KEY，非对称性可肯定就是加密和解密不能使用同一个KEY了，那就是我们的公钥和私钥，公钥加密私钥解密，把我们的KEY通过公钥加密之后上传服务器，服务端拿到之后通过私钥解密就拿到了KEY，再去解密我们的AES数据，有同学会想，前面说我们的AES的KEY可能会被劫持，那加了密被劫持呢，放心被劫持到的也是我们通过公钥加密的，想要得知真正的KEY就得知道我们的私钥，可私钥在我们服务端要想拿到除非有了间谍，不然是没法解开真正的KEY的，还有人可能会想，我们使用公钥加密的KEY我们的公钥就要保存在我们移动端的本地了，那别人拿到公钥之后会不会解开劫持得到的数据呢，不会的，因为公钥加密的只能用私钥解开。

 

三：解释完成，该上代码了

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      我们先看RSA加密的代码，代码具体的都有注释，使用时候需要我们注意的我们在下面说，下面是这个.m文件的代码：

#import "RSAEncryptor.h"#import 
     
      @implementation RSAEncryptorstatic NSString *base64_encode_data(NSData *data){    data = [data base64EncodedDataWithOptions:0];    NSString *ret = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];    return ret;}static NSData *base64_decode(NSString *str){    NSData *data = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];    return data;}#pragma mark - 使用'.der'公钥文件加密//加密+ (NSString *)encryptString:(NSString *)str publicKeyWithContentsOfFile:(NSString *)path{    if (!str || !path)  return nil;    return [self encryptString:str publicKeyRef:[self getPublicKeyRefWithContentsOfFile:path]];}//获取公钥+ (SecKeyRef)getPublicKeyRefWithContentsOfFile:(NSString *)filePath{    NSData *certData = [NSData dataWithContentsOfFile:filePath];    if (!certData) {        return nil;    }    SecCertificateRef cert = SecCertificateCreateWithData(NULL, (CFDataRef)certData);    SecKeyRef key = NULL;    SecTrustRef trust = NULL;    SecPolicyRef policy = NULL;    if (cert != NULL) {        policy = SecPolicyCreateBasicX509();        if (policy) {            if (SecTrustCreateWithCertificates((CFTypeRef)cert, policy, &trust) == noErr) {                SecTrustResultType result;                if (SecTrustEvaluate(trust, &result) == noErr) {                    key = SecTrustCopyPublicKey(trust);                }            }        }    }    if (policy) CFRelease(policy);    if (trust) CFRelease(trust);    if (cert) CFRelease(cert);    return key;}+ (NSString *)encryptString:(NSString *)str publicKeyRef:(SecKeyRef)publicKeyRef{    if(![str dataUsingEncoding:NSUTF8StringEncoding]){        return nil;    }    if(!publicKeyRef){        return nil;    }    NSData *data = [self encryptData:[str dataUsingEncoding:NSUTF8StringEncoding] withKeyRef:publicKeyRef];    NSString *ret = base64_encode_data(data);    return ret;}#pragma mark - 使用'.12'私钥文件解密//解密+ (NSString *)decryptString:(NSString *)str privateKeyWithContentsOfFile:(NSString *)path password:(NSString *)password{    if (!str || !path) return nil;    if (!password) password = @"";    return [self decryptString:str privateKeyRef:[self getPrivateKeyRefWithContentsOfFile:path password:password]];}//获取私钥+ (SecKeyRef)getPrivateKeyRefWithContentsOfFile:(NSString *)filePath password:(NSString*)password{        NSData *p12Data = [NSData dataWithContentsOfFile:filePath];    if (!p12Data) {        return nil;    }    SecKeyRef privateKeyRef = NULL;    NSMutableDictionary * options = [[NSMutableDictionary alloc] init];    [options setObject: password forKey:(__bridge id)kSecImportExportPassphrase];    CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL);    OSStatus securityError = SecPKCS12Import((__bridge CFDataRef) p12Data, (__bridge CFDictionaryRef)options, &items);    if (securityError == noErr && CFArrayGetCount(items) > 0) {        CFDictionaryRef identityDict = CFArrayGetValueAtIndex(items, 0);        SecIdentityRef identityApp = (SecIdentityRef)CFDictionaryGetValue(identityDict, kSecImportItemIdentity);        securityError = SecIdentityCopyPrivateKey(identityApp, &privateKeyRef);        if (securityError != noErr) {            privateKeyRef = NULL;        }    }    CFRelease(items);    return privateKeyRef;}+ (NSString *)decryptString:(NSString *)str privateKeyRef:(SecKeyRef)privKeyRef{    NSData *data = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];    if (!privKeyRef) {        return nil;    }    data = [self decryptData:data withKeyRef:privKeyRef];    NSString *ret = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];    return ret;}#pragma mark - 使用公钥字符串加密/* START: Encryption with RSA public key *///使用公钥字符串加密+ (NSString *)encryptString:(NSString *)str publicKey:(NSString *)pubKey{    NSData *data = [self encryptData:[str dataUsingEncoding:NSUTF8StringEncoding] publicKey:pubKey];    NSString *ret = base64_encode_data(data);    return ret;}+ (NSData *)encryptData:(NSData *)data publicKey:(NSString *)pubKey{    if(!data || !pubKey){        return nil;    }    SecKeyRef keyRef = [self addPublicKey:pubKey];    if(!keyRef){        return nil;    }    return [self encryptData:data withKeyRef:keyRef];}+ (SecKeyRef)addPublicKey:(NSString *)key{    NSRange spos = [key rangeOfString:@"-----BEGIN PUBLIC KEY-----"];    NSRange epos = [key rangeOfString:@"-----END PUBLIC KEY-----"];    if(spos.location != NSNotFound && epos.location != NSNotFound){        NSUInteger s = spos.location + spos.length;        NSUInteger e = epos.location;        NSRange range = NSMakeRange(s, e-s);        key = [key substringWithRange:range];    }    key = [key stringByReplacingOccurrencesOfString:@"\r" withString:@""];    key = [key stringByReplacingOccurrencesOfString:@"\n" withString:@""];    key = [key stringByReplacingOccurrencesOfString:@"\t" withString:@""];    key = [key stringByReplacingOccurrencesOfString:@" "  withString:@""];        // This will be base64 encoded, decode it.    NSData *data = base64_decode(key);    data = [self stripPublicKeyHeader:data];    if(!data){        return nil;    }        //a tag to read/write keychain storage    NSString *tag = @"RSAUtil_PubKey";    NSData *d_tag = [NSData dataWithBytes:[tag UTF8String] length:[tag length]];        // Delete any old lingering key with the same tag    NSMutableDictionary *publicKey = [[NSMutableDictionary alloc] init];    [publicKey setObject:(__bridge id) kSecClassKey forKey:(__bridge id)kSecClass];    [publicKey setObject:(__bridge id) kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];    [publicKey setObject:d_tag forKey:(__bridge id)kSecAttrApplicationTag];    SecItemDelete((__bridge CFDictionaryRef)publicKey);        // Add persistent version of the key to system keychain    [publicKey setObject:data forKey:(__bridge id)kSecValueData];    [publicKey setObject:(__bridge id) kSecAttrKeyClassPublic forKey:(__bridge id)     kSecAttrKeyClass];    [publicKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)     kSecReturnPersistentRef];        CFTypeRef persistKey = nil;    OSStatus status = SecItemAdd((__bridge CFDictionaryRef)publicKey, &persistKey);    if (persistKey != nil){        CFRelease(persistKey);    }    if ((status != noErr) && (status != errSecDuplicateItem)) {        return nil;    }        [publicKey removeObjectForKey:(__bridge id)kSecValueData];    [publicKey removeObjectForKey:(__bridge id)kSecReturnPersistentRef];    [publicKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];    [publicKey setObject:(__bridge id) kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];        // Now fetch the SecKeyRef version of the key    SecKeyRef keyRef = nil;    status = SecItemCopyMatching((__bridge CFDictionaryRef)publicKey, (CFTypeRef *)&keyRef);    if(status != noErr){        return nil;    }    return keyRef;}+ (NSData *)stripPublicKeyHeader:(NSData *)d_key{    // Skip ASN.1 public key header    if (d_key == nil) return(nil);        unsigned long len = [d_key length];    if (!len) return(nil);        unsigned char *c_key = (unsigned char *)[d_key bytes];    unsigned int  idx     = 0;        if (c_key[idx++] != 0x30) return(nil);        if (c_key[idx] > 0x80) idx += c_key[idx] - 0x80 + 1;    else idx++;        // PKCS #1 rsaEncryption szOID_RSA_RSA    static unsigned char seqiod[] =    { 0x30,   0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01,        0x01, 0x05, 0x00 };    if (memcmp(&c_key[idx], seqiod, 15)) return(nil);    idx += 15;    if (c_key[idx++] != 0x03) return(nil);    if (c_key[idx] > 0x80) idx += c_key[idx] - 0x80 + 1;    else idx++;    if (c_key[idx++] != '\0') return(nil);    // Now make a new NSData from this buffer    return ([NSData dataWithBytes:&c_key[idx] length:len - idx]);}+ (NSData *)encryptData:(NSData *)data withKeyRef:(SecKeyRef) keyRef{    const uint8_t *srcbuf = (const uint8_t *)[data bytes];    size_t srclen = (size_t)data.length;        size_t block_size = SecKeyGetBlockSize(keyRef) * sizeof(uint8_t);    void *outbuf = malloc(block_size);    size_t src_block_size = block_size - 11;        NSMutableData *ret = [[NSMutableData alloc] init];    for(int idx=0; idx
      
        src_block_size){            data_len = src_block_size;        }        size_t outlen = block_size;        OSStatus status = noErr;        status = SecKeyEncrypt(keyRef,                               kSecPaddingPKCS1,                               srcbuf + idx,                               data_len,                               outbuf,                               &outlen                               );        if (status != 0) {            NSLog(@"SecKeyEncrypt fail. Error Code: %d", status);            ret = nil;            break;        }else{            [ret appendBytes:outbuf length:outlen];        }    }    free(outbuf);    CFRelease(keyRef);    return ret;}/* END: Encryption with RSA public key */ #pragma mark - 使用私钥字符串解密/* START: Decryption with RSA private key *///使用私钥字符串解密+ (NSString *)decryptString:(NSString *)str privateKey:(NSString *)privKey{    if (!str) return nil;    NSData *data = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];    data = [self decryptData:data privateKey:privKey];    NSString *ret = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];    return ret;}+ (NSData *)decryptData:(NSData *)data privateKey:(NSString *)privKey{    if(!data || !privKey){        return nil;    }    SecKeyRef keyRef = [self addPrivateKey:privKey];    if(!keyRef){        return nil;    }    return [self decryptData:data withKeyRef:keyRef];}+ (SecKeyRef)addPrivateKey:(NSString *)key{    NSRange spos = [key rangeOfString:@"-----BEGIN RSA PRIVATE KEY-----"];    NSRange epos = [key rangeOfString:@"-----END RSA PRIVATE KEY-----"];    if(spos.location != NSNotFound && epos.location != NSNotFound){        NSUInteger s = spos.location + spos.length;        NSUInteger e = epos.location;        NSRange range = NSMakeRange(s, e-s);        key = [key substringWithRange:range];    }    key = [key stringByReplacingOccurrencesOfString:@"\r" withString:@""];    key = [key stringByReplacingOccurrencesOfString:@"\n" withString:@""];    key = [key stringByReplacingOccurrencesOfString:@"\t" withString:@""];    key = [key stringByReplacingOccurrencesOfString:@" "  withString:@""];        // This will be base64 encoded, decode it.    NSData *data = base64_decode(key);    data = [self stripPrivateKeyHeader:data];    if(!data){        return nil;    }        //a tag to read/write keychain storage    NSString *tag = @"RSAUtil_PrivKey";    NSData *d_tag = [NSData dataWithBytes:[tag UTF8String] length:[tag length]];        // Delete any old lingering key with the same tag    NSMutableDictionary *privateKey = [[NSMutableDictionary alloc] init];    [privateKey setObject:(__bridge id) kSecClassKey forKey:(__bridge id)kSecClass];    [privateKey setObject:(__bridge id) kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];    [privateKey setObject:d_tag forKey:(__bridge id)kSecAttrApplicationTag];    SecItemDelete((__bridge CFDictionaryRef)privateKey);        // Add persistent version of the key to system keychain    [privateKey setObject:data forKey:(__bridge id)kSecValueData];    [privateKey setObject:(__bridge id) kSecAttrKeyClassPrivate forKey:(__bridge id)     kSecAttrKeyClass];    [privateKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)     kSecReturnPersistentRef];        CFTypeRef persistKey = nil;    OSStatus status = SecItemAdd((__bridge CFDictionaryRef)privateKey, &persistKey);    if (persistKey != nil){        CFRelease(persistKey);    }    if ((status != noErr) && (status != errSecDuplicateItem)) {        return nil;    }    [privateKey removeObjectForKey:(__bridge id)kSecValueData];    [privateKey removeObjectForKey:(__bridge id)kSecReturnPersistentRef];    [privateKey setObject:[NSNumber numberWithBool:YES] forKey:(__bridge id)kSecReturnRef];    [privateKey setObject:(__bridge id) kSecAttrKeyTypeRSA forKey:(__bridge id)kSecAttrKeyType];        // Now fetch the SecKeyRef version of the key    SecKeyRef keyRef = nil;    status = SecItemCopyMatching((__bridge CFDictionaryRef)privateKey, (CFTypeRef *)&keyRef);    if(status != noErr){        return nil;    }    return keyRef;}+ (NSData *)stripPrivateKeyHeader:(NSData *)d_key{    // Skip ASN.1 private key header    if (d_key == nil) return(nil);        unsigned long len = [d_key length];    if (!len) return(nil);        unsigned char *c_key = (unsigned char *)[d_key bytes];    unsigned int  idx     = 22; //magic byte at offset 22        if (0x04 != c_key[idx++]) return nil;        //calculate length of the key    unsigned int c_len = c_key[idx++];    int det = c_len & 0x80;    if (!det) {        c_len = c_len & 0x7f;    } else {        int byteCount = c_len & 0x7f;        if (byteCount + idx > len) {            //rsa length field longer than buffer            return nil;        }        unsigned int accum = 0;        unsigned char *ptr = &c_key[idx];        idx += byteCount;        while (byteCount) {            accum = (accum << 8) + *ptr;            ptr++;            byteCount--;        }        c_len = accum;    }    // Now make a new NSData from this buffer    return [d_key subdataWithRange:NSMakeRange(idx, c_len)];}+ (NSData *)decryptData:(NSData *)data withKeyRef:(SecKeyRef) keyRef{    const uint8_t *srcbuf = (const uint8_t *)[data bytes];    size_t srclen = (size_t)data.length;        size_t block_size = SecKeyGetBlockSize(keyRef) * sizeof(uint8_t);    UInt8 *outbuf = malloc(block_size);    size_t src_block_size = block_size;        NSMutableData *ret = [[NSMutableData alloc] init];    for(int idx=0; idx
       
         src_block_size){            data_len = src_block_size;        }                size_t outlen = block_size;        OSStatus status = noErr;        status = SecKeyDecrypt(keyRef,                               kSecPaddingNone,                               srcbuf + idx,                               data_len,                               outbuf,                               &outlen                               );        if (status != 0) {            NSLog(@"SecKeyEncrypt fail. Error Code: %d", status);            ret = nil;            break;        }else{            //the actual decrypted data is in the middle, locate it!            int idxFirstZero = -1;            int idxNextZero = (int)outlen;            for ( int i = 0; i < outlen; i++ ) {                if ( outbuf[i] == 0 ) {                    if ( idxFirstZero < 0 ) {                        idxFirstZero = i;                    } else {                        idxNextZero = i;                        break;                    }                }            }                        [ret appendBytes:&outbuf[idxFirstZero+1] length:idxNextZero-idxFirstZero-1];        }    }    free(outbuf);    CFRelease(keyRef);    return ret;}/* END: Decryption with RSA private key */@end
       
      
     

 

      注意： 在我们使用RSA的p12文件解密的时候 也就是使用下面这个方法的时候：

   + (NSString *)decryptString:(NSString *)str privateKeyWithContentsOfFile:(NSString *)path password:(NSString *)password

      使用到的 password 的这个参数就是我们给 p12文件设置的密码。这也是为什么前面我们说的你的记住这个密码的原因，不然你只能重新生成了。当然服务端解密的时候是不需要的。

      path 这个参数就是你的p12文件在你本地的路径，这个就自己写了。

 

四：AES呢

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      首先的说说AES我们需要注意的几个点：

      1、加密位数   128还是256的这个得几个端统一不能说你用256的服务端解的时候用128的。

      2、IV 初始向量  这个也得统一，一般128的加密位数使用16位的初始向量

      3、具体的AES加密代码的注释我在前面的博客中有写，它里面参数的含义是什么都有说明，这里就简单的看一下128加密代码，要是想看这个加密方法的具体说明，找一下以前的博客。

     4、string的加密解密还是归结到data的加密解密了，先看data的加密解密：

#import "NSData+AES.h"static NSString * const AES_IV = @"自己定义";@implementation NSData (AES)- (NSData *)aes128_encrypt:(NSString *)key   //加密{    // kCCKeySizeAES256是加密位数    /*     enum {     kCCKeySizeAES128          = 16,     kCCKeySizeAES192          = 24,     kCCKeySizeAES256          = 32,     kCCKeySizeDES             = 8,     kCCKeySize3DES            = 24,     kCCKeySizeMinCAST         = 5,     kCCKeySizeMaxCAST         = 16,     kCCKeySizeMinRC4          = 1,     kCCKeySizeMaxRC4          = 512,     kCCKeySizeMinRC2          = 1,     kCCKeySizeMaxRC2          = 128,     kCCKeySizeMinBlowfish     = 8,     kCCKeySizeMaxBlowfish     = 56,     };     */    char keyPtr[kCCKeySizeAES128+1];    bzero(keyPtr, sizeof(keyPtr));    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];        NSUInteger dataLength = [self length];    size_t bufferSize = dataLength + kCCBlockSizeAES128;    void * buffer = malloc(bufferSize);    size_t numBytesEncrypted = 0;        //    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,                                          kCCOptionPKCS7Padding,                                          keyPtr, kCCBlockSizeAES128,                                          [AES_IV UTF8String],                                          [self bytes], dataLength,                                          buffer, bufferSize,                                          &numBytesEncrypted);    if (cryptStatus == kCCSuccess) {        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];    }    free(buffer);    return nil;}- (NSData *)aes128_decrypt:(NSString *)key   //解密{    char keyPtr[kCCKeySizeAES128+1];    bzero(keyPtr, sizeof(keyPtr));    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];        NSUInteger dataLength = [self length];    size_t bufferSize = dataLength + kCCBlockSizeAES128;    void *buffer = malloc(bufferSize);    size_t numBytesDecrypted = 0;    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,                                          kCCOptionPKCS7Padding ,                                          keyPtr, kCCBlockSizeAES128,                                          [AES_IV UTF8String],                                          [self bytes], dataLength,                                          buffer, bufferSize,                                          &numBytesDecrypted);    if (cryptStatus == kCCSuccess) {        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];            }    free(buffer);    return nil;}

      5、String的加密解密 128 位的代码如下：

// 利用Key加密字符串-(NSString *) aes_encrypt:(NSString *)key{        const char *cstr = [self cStringUsingEncoding:NSUTF8StringEncoding];    NSData *data = [NSData dataWithBytes:cstr length:self.length];    //对数据进行加密    NSData *result = [data aes128_encrypt:key];        //转换为2进制字符串    if (result && result.length > 0) {                Byte *datas = (Byte*)[result bytes];        NSMutableString *output = [NSMutableString stringWithCapacity:result.length * 2];        for(int i = 0; i < result.length; i++){            [output appendFormat:@"%02x", datas[i]];        }        return output;    }    return nil;}//利用Key解密字符串-(NSString *) aes_decrypt:(NSString *)key{        //转换为2进制Data    NSMutableData *data = [NSMutableData dataWithCapacity:self.length / 2];    unsigned char whole_byte;    char byte_chars[3] = {'\0','\0','\0'};    int i;    for (i=0; i < [self length] / 2; i++) {        byte_chars[0] = [self characterAtIndex:i*2];        byte_chars[1] = [self characterAtIndex:i*2+1];        whole_byte = strtol(byte_chars, NULL, 16);        [data appendBytes:&whole_byte length:1];    }        //对数据进行解密    NSData* result = [data aes128_decrypt:key];    if (result && result.length > 0) {        return [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding];    }    return nil;}