AES（The Advanced Encryption Standard）

AES是美國國家標準與技術研究所用于加密電子數(shù)據(jù)的規(guī)范。它被預期能成為人們公認的加密包括金融、電信和政府數(shù)字信息的方法

AES 是一個迭代的、對稱密鑰分組的密碼，它可以使用128、192 和 256 位密鑰，并且用 128 位（16字節(jié)）分組加密和解密數(shù)據(jù)。與公共密鑰密碼使用密鑰對不同，對稱密鑰密碼使用相同的密鑰加密和解密數(shù)據(jù)。通過分組密碼返回的加密數(shù)據(jù) 的位數(shù)與輸入數(shù)據(jù)相同。迭代加密使用一個循環(huán)結(jié)構(gòu)，在該循環(huán)中重復置換（permutations ）和替換(substitutions）輸入數(shù)據(jù)。

目前在商業(yè)App中使用的最多的是RSA與AES加密方式，兩種加密各種所長，所幸目前都有接觸過。

iOS中的使用

新建MySecurity類，繼承于NSObject

.h文件
<pre><code class='Xcode'>

import <Foundation/Foundation.h>

@interface MySecurity : NSObject

pragma mark -根據(jù)密匙初始化

-(instancetype) initWithKey:(NSString *) key;

pragma mark -加密

-(NSString *) AES256EncryptWithString:(NSString *) str;

pragma mark -解密

-(NSString *) AES256DecryptWithString:(NSString *) str;

pragma mark -獲取安全密匙

+(NSString*) getSecurityKey;

@end
</code></pre>
.m文件
<pre><code class='Xcode'>

import "MySecurity.h"

import "NSData+AES256.h"

import "NSString+MD5.h"

@interface MySecurity ()
@property(strong,nonatomic) NSString *key;

@end

@implementation MySecurity

pragma mark -獲取安全鑰匙

+(NSString*) getSecurityKey
{
return @"加密的密匙";
}

pragma mark -更加密碼密匙初始化

-(instancetype) initWithKey:(NSString *) key
{
self = [super init];
if (self)
{
self.key = key;
}
return self;
}

pragma mark -加密

-(NSString *) AES256EncryptWithString:(NSString *) str
{
NSData *dt1 = [str dataUsingEncoding:NSUTF8StringEncoding];

NSData *dt2 = [dt1 AES256EncryptWithKey:[self.key MD5]];

 NSString *str2 = [dt2 base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
return str2;

}

pragma mark -解密

-(NSString *) AES256DecryptWithString:(NSString *) str
{
NSData *dt3 = [[NSData alloc] initWithBase64EncodedString:str options:NSDataBase64DecodingIgnoreUnknownCharacters];

NSData *dt4 = [dt3 AES256DecryptWithKey:[self.key MD5]];

NSString *str4 = [[NSString alloc] initWithData:dt4 encoding:NSUTF8StringEncoding];
return str4;

}

@end
</code></pre>

需要用到的NSData+AES256分類與NSString+MD5分類

<pre><code class='Xcode'>

//---------------NSData (AES256)頭文件------------

import <Foundation/Foundation.h>

@interface NSData (AES256)

/*
加密
(NSString*)key 32位秘鑰
返回加密后的 NSData
*/

• (NSData)AES256EncryptWithKey:(NSString)key ;

/*
解密
(NSString*)key 32位秘鑰
返回解密后的 NSData
*/

• (NSData)AES256DecryptWithKey:(NSString)key ;

@end

//---------------NSData (AES256)實現(xiàn)文件------------

import "NSData+AES256.h"

import <CommonCrypto/CommonCryptor.h>

@implementation NSData (AES256)

• (NSData)AES256EncryptWithKey:(NSString)key {

  char keyPtr[kCCKeySizeAES256 +1]; // room for terminator (unused)
  bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)

  [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|kCCOptionECBMode,
  keyPtr,
  kCCKeySizeAES256,
  NULL /* initialization vector (optional) /,
  [self bytes],
  dataLength, / input /
  buffer,
  bufferSize, / output */
  &numBytesEncrypted);

if (cryptStatus == kCCSuccess) {
    return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}

free(buffer);
return nil;

}

• (NSData)AES256DecryptWithKey:(NSString)key {

  char keyPtr[kCCKeySizeAES256+1 ]; // room for terminator (unused)
  bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)

// fetch key data
[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|kCCOptionECBMode,
                                      keyPtr,
                                      kCCKeySizeAES256,
                                      NULL /* initialization vector (optional) */,
                                      [self bytes],
                                      dataLength, /* input */
                                      buffer,
                                      bufferSize, /* output */
                                      &numBytesDecrypted);

if (cryptStatus == kCCSuccess) {
    return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
}

free(buffer); //free the buffer;
return nil;

}

@end

//---------------NSString (MD5)頭文件------------

import <Foundation/Foundation.h>

@interface NSString (MD5)
/*
獲取字符串的MD5值
返回32位MD5值
/
-(NSString) MD5;

@end

//---------------NSString (MD5)實現(xiàn)文件------------

import "NSString+MD5.h"

import <CommonCrypto/CommonDigest.h>

@implementation NSString (MD5)

pragma mark -MD5加密

-(NSString*) MD5
{
const char * cStrValue = [self UTF8String];
unsigned char theResult[CC_MD5_DIGEST_LENGTH];

CC_MD5(cStrValue, (CC_LONG)strlen(cStrValue), theResult);
return [NSString stringWithFormat:@"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
        theResult[0], theResult[1], theResult[2], theResult[3],
        theResult[4], theResult[5], theResult[6], theResult[7],
        theResult[8], theResult[9], theResult[10], theResult[11],
        theResult[12], theResult[13], theResult[14], theResult[15]];

}

@end
</code></pre>

使用

<pre><code class='Xcode'>
//初始化對象
MySecurity *security = [[MySecurity alloc] initWithKey:[MySecurity getSecurityKey]];
//加密
NSString * str1 = [security AES256EncryptWithString:@"要加密的內(nèi)容"];

//解密
NSString * str2 = [security AES256DecryptWithString:@"要解密的內(nèi)容"];

</code></pre>

總的來說，使用還是很簡單的，希望能幫助到大家。

end