一、AES简介

高级加密标准（英语：Advanced Encryption Standard，缩写：AES），在密码学中又称Rijndael加密法。AES是一个对称分组密码算法，旨在取代DES成为广泛使用的标准。根据使用的密码长度，AES最常见的有3种方案，用以适应不同的场景要求，分别是AES-128、AES-192和AES-256。

二、算法描述

AES1

AES2

三、算法实现

@implementation CATSecurity

#pragma mark --
#pragma mark -- AES

/**
 *  get data's aes256 encrypt data
 *
 *  @param data source data
 *  @param key  key for encrypt/decrypt  !!!key length must be 16
 *
 *  @return aes256 encrypt data
 */
+(NSData *)aes256EncryptWithData:(NSData *)data key:(NSString *)key{
    if (!key || key.length !=16) {
        NSLog(@"key length must be 16");
        return nil;
    }
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    NSUInteger dataLength = data.length;
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          data.bytes, dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    free(buffer);
    return nil;
}

/**
 *  get source data from aes256 encrypt data
 *
 *  @param data aes256 encrypt data
 *  @param key  key for encrypt/decrypt  !!!key length must be 16
 *
 *  @return source data
 */
+(NSData *)aes256DecryptWithData:(NSData *)data key:(NSString *)key{
    if (!key || key.length !=16) {
        NSLog(@"key length must be 16");
        return nil;
    }
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
    NSUInteger dataLength = data.length;
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          data.bytes, dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }
    free(buffer);
    return nil;
}

/**
 *  get string's aes256 encrypt data
 *
 *  @param string source string
 *  @param key  key for encrypt/decrypt  !!!key length must be 16
 *
 *  @return aes256 encrypt data
 */
+(NSData*)aes256EncryptWithString:(NSString*)string key:(NSString *)key{
    if (!key || key.length !=16) {
        NSLog(@"key length must be 16");
        return nil;
    }
    NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
    NSData *encryptedData = [self aes256EncryptWithData:data key:key];
    return encryptedData;
}

/**
 *  get source string from aes256 encrypt data
 *
 *  @param data aes256 encrypt data
 *  @param key  key for encrypt/decrypt  !!!key length must be 16
 *
 *  @return source string
 */
+(NSString*)aes256DecryptStringWithData:(NSData *)data key:(NSString *)key{
    if (!key || key.length !=16) {
        NSLog(@"key length must be 16");
        return nil;
    }
    NSData *decryData = [self aes256DecryptWithData:data key:key];
    NSString *string = [[NSString alloc] initWithData:decryData encoding:NSUTF8StringEncoding];
    return string;
}

@end

四、补充

由于iOS、java的平台差异，AES的加密算法存在兼容性问题(iOS的AES Padding只支持ccPKCS7Padding, ccNoPadding)，为了使用方便，我找了一份可兼容的Java的代码并做了测试，详见工程的java目录。