iOS開發中AES的加密和解密

關於AES的介紹請參考AES演算法詳解，這裡我就不多介紹了，我主要介紹到我們專案中用到的AES加密和解密的使用方法。

建立內方法

//AES加密和解密

+(NSString*)AesEncrypt:(NSString*)str;

+(NSString*)AesDecrypt:(NSString*)str;

在.m檔案裡程式碼如下

AES加密

+(NSString*)AesEncrypt:(NSString*)str{

NSString*key=@"X*Z_j2#3%z5&H+M4";//金鑰

NSData*data=[strdataUsingEncoding:NSUTF8StringEncoding];//待加密字元轉為NSData型

charkeyPtr[kCCKeySizeAES128+1];

memset(keyPtr,0,sizeof(keyPtr));

[key getCString:keyPtrmaxLength:sizeof(keyPtr)encoding:NSUTF8StringEncoding];

NSUIntegerdataLength = [datalength];

size_tbufferSize = dataLength +kCCBlockSizeAES128;

void*buffer =malloc(bufferSize);

size_tnumBytesCrypted =0;

CCCryptorStatuscryptStatus =CCCrypt(

      kCCEncrypt,    //  加密    kCCDecrypt解密

      kCCAlgorithmAES128,    //填充方式

     kCCOptionPKCS7Padding|kCCOptionECBMode,      //工作模式

      keyPtr,  //AES的金鑰長度有128位元組、192位元組、256位元組幾種，這裡舉出可能存在的最大長度

      kCCBlockSizeAES128,      //密文長度+補位長度

      nil,     //偏移量，由於是對稱加密，用不到

      [databytes],   //位元組大小

      dataLength,    //位元組長度

      buffer,       

      bufferSize,  

      &numBytesCrypted);

if(cryptStatus ==kCCSuccess) {

NSData*resultData=[NSDatadataWithBytesNoCopy:bufferlength:numBytesCrypted];

NSString*result =[selfbase64EncodedStringFrom:resultData];

returnresult;

}

free(buffer);

returnstr;

}

解密操作：

+(NSString*)AesDecrypt:(NSString*)str{

NSString*key=@"X*Z_j2#3%z5&H+M4";M  //金鑰

NSData*data=[selfdataWithBase64EncodedString:str];// base4解碼

charkeyPtr[kCCKeySizeAES128+1];

memset(keyPtr,0,sizeof(keyPtr));

[keygetCString:keyPtrmaxLength:sizeof(keyPtr)encoding:NSUTF8StringEncoding];

NSUIntegerdataLength = [datalength];

size_tbufferSize = dataLength +kCCBlockSizeAES128;

void*buffer =malloc(bufferSize);

size_tnumBytesCrypted =0;

CCCryptorStatuscryptStatus =CCCrypt(kCCDecrypt,

kCCAlgorithmAES128,

kCCOptionPKCS7Padding|kCCOptionECBMode,

keyPtr,

kCCBlockSizeAES128,

nil,

[databytes],

dataLength,

buffer,

bufferSize,

&numBytesCrypted);

if(cryptStatus ==kCCSuccess) {

NSData*resultData=[NSDatadataWithBytesNoCopy:bufferlength:numBytesCrypted];

NSString*result =[[NSStringalloc]initWithData:resultDataencoding:NSUTF8StringEncoding];

returnresult;

}

free(buffer);

returnstr;

}

總結一下：

常見的字元編碼有：UTF-8、ASCII、Base64、十六進位制等等，不要使用UTF-8，加密過程是使用UTF-8完成的，但是加密完後的NSData無法通過UTF-8編碼格式轉出成NSString，推薦使用Base64編碼或者十六進位制編碼，取決於後臺。另外加密的資料長度大於10位的情況下，工作模式不要只寫kCCOptionPKCS7Padding要把kCCOptionECBMode也加上，請測在密文在16位以上解密以後跟後臺不一致，加上kCCOptionECBMode會解決.

以下是base64的編碼和解碼

.m檔案加上這個

#import  <CommonCrypto/CommonCryptor.h>

static constcharencodingTable[] ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

#define LocalStr_None @""//空字串

+ (NSString*)base64StringFromText:(NSString*)text

{

if(text && ![textisEqualToString:LocalStr_None]) {

NSData*data = [textdataUsingEncoding:NSUTF8StringEncoding];

return[selfbase64EncodedStringFrom:data];

}

else{

returnLocalStr_None;

}

}

+ (NSString*)textFromBase64String:(NSString*)base64

{

if(base64 && ![base64isEqualToString:LocalStr_None]) {

NSData*data = [selfdataWithBase64EncodedString:base64];

return[[NSStringalloc]initWithData:dataencoding:NSUTF8StringEncoding];

}

else{

returnLocalStr_None;

}

}

+ (NSData*)dataWithBase64EncodedString:(NSString*)string

{

if(string ==nil)

[NSExceptionraise:NSInvalidArgumentExceptionformat:nil];

if([stringlength] ==0)

return[NSDatadata];

staticchar*decodingTable =NULL;

if(decodingTable ==NULL)

{

decodingTable =malloc(256);

if(decodingTable ==NULL)

returnnil;

memset(decodingTable,CHAR_MAX,256);

NSUIntegeri;

for(i =0; i <64; i++)

decodingTable[(short)encodingTable[i]] = i;

}

constchar*characters = [stringcStringUsingEncoding:NSASCIIStringEncoding];

if(characters ==NULL)//Not an ASCII string!

returnnil;

char*bytes =malloc((([stringlength] +3) /4) *3);

if(bytes ==NULL)

returnnil;

NSUIntegerlength =0;

NSUIntegeri =0;

while(YES)

{

charbuffer[4];

shortbufferLength;

for(bufferLength =0; bufferLength <4; i++)

{

if(characters[i] =='\0')

break;

if(isspace(characters[i]) || characters[i] =='=')

continue;

buffer[bufferLength] = decodingTable[(short)characters[i]];

if(buffer[bufferLength++] ==CHAR_MAX)//Illegal character!

{

free(bytes);

returnnil;

}

}

if(bufferLength ==0)

break;

if(bufferLength ==1)//At least two characters are needed to produce one byte!

{

free(bytes);

returnnil;

}

//Decode the characters in the buffer to bytes.

bytes[length++] = (buffer[0] <<2) | (buffer[1] >>4);

if(bufferLength >2)

bytes[length++] = (buffer[1] <<4) | (buffer[2] >>2);

if(bufferLength >3)

bytes[length++] = (buffer[2] <<6) | buffer[3];

}

bytes =realloc(bytes, length);

return[NSDatadataWithBytesNoCopy:byteslength:length];

}

+ (NSString*)base64EncodedStringFrom:(NSData*)data

{

if([datalength] ==0)

return@"";

char*characters =malloc((([datalength] +2) /3) *4);

if(characters ==NULL)

returnnil;

NSUIntegerlength =0;

NSUIntegeri =0;

while(i < [datalength])

{

charbuffer[3] = {0,0,0};

shortbufferLength =0;

while(bufferLength <3&& i < [datalength])

buffer[bufferLength++] = ((char*)[databytes])[i++];

//Encode the bytes in the buffer to four characters, including padding "=" characters if necessary.

characters[length++] =encodingTable[(buffer[0] &0xFC) >>2];

characters[length++] =encodingTable[((buffer[0] &0x03) <<4) | ((buffer[1] &0xF0) >>4)];

if(bufferLength >1)

characters[length++] =encodingTable[((buffer[1] &0x0F) <<2) | ((buffer[2] &0xC0) >>6)];

elsecharacters[length++] ='=';

if(bufferLength >2)

characters[length++] =encodingTable[buffer[2] &0x3F];

elsecharacters[length++] ='=';

}

 return   [[NSStringalloc]initWithBytesNoCopy:characterslength:lengthencoding:NSASCIIStringEncodin   gfreeWhenDone:YES];

}