AES（The Advanced Encryption Standard）

AES是美国国家标准与技术研究所用于加密电子数据的规范。它被预期能成为人们公认的加密包括金融、电信和政府数字信息的方法

AES 是一个迭代的、对称密钥分组的密码，它可以使用128、192 和 256 位密钥，并且用 128 位（16字节）分组加密和解密数据。与公共密钥密码使用密钥对不同，对称密钥密码使用相同的密钥加密和解密数据。通过分组密码返回的加密数据 的位数与输入数据相同。迭代加密使用一个循环结构，在该循环中重复置换（permutations ）和替换(substitutions）输入数据。

目前在商业App中使用的最多的是RSA与AES加密方式，两种加密各种所长，所幸目前都有接触过。

iOS中的使用

新建MySecurity类，继承于NSObject

.h文件
<pre><code class='Xcode'>

import <Foundation/Foundation.h>

@interface MySecurity : NSObject

pragma mark -根据密匙初始化

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

pragma mark -加密

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

pragma mark -解密

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

pragma mark -获取安全密匙

+(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 -获取安全钥匙

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

pragma mark -更加密码密匙初始化

-(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分类与NSString+MD5分类

<pre><code class='Xcode'>

//---------------NSData (AES256)头文件------------

import <Foundation/Foundation.h>

@interface NSData (AES256)

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

• (NSData)AES256EncryptWithKey:(NSString)key ;

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

• (NSData)AES256DecryptWithKey:(NSString)key ;

@end

//---------------NSData (AES256)实现文件------------

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)头文件------------

import <Foundation/Foundation.h>

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

@end

//---------------NSString (MD5)实现文件------------

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'>
//初始化对象
MySecurity *security = [[MySecurity alloc] initWithKey:[MySecurity getSecurityKey]];
//加密
NSString * str1 = [security AES256EncryptWithString:@"要加密的内容"];

//解密
NSString * str2 = [security AES256DecryptWithString:@"要解密的内容"];

</code></pre>

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总的来说，使用还是很简单的，希望能帮助到大家。

end