objective-c aes加密

在cocoa看到的加密代码，介绍一下。
aes加密的，1M的数据，0.1秒以内，速度还可以接受。

@interface NSData (AESAdditions)

- (NSData*)AES256EncryptWithKey:(NSString*)key;
- (NSData*)AES256DecryptWithKey:(NSString*)key;

@end

#import <CommonCrypto/CommonCryptor.h>

@implementation NSData (AESAdditions)

- (NSData*)AES256EncryptWithKey:(NSString*)key {
    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    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];
   
    //See the doc: For block ciphers, the output size will always be less than or
    //equal to the input size plus the size of one block.
    //That's why we need to add the size of one block here
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void* buffer = malloc(bufferSize);
   
    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesEncrypted);
   
    if (cryptStatus == kCCSuccess)
    {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSMutableData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
   
    free(buffer); //free the buffer;
    return nil;
}

- (NSData*)AES256DecryptWithKey:(NSString*)key {
    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    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];
   
    //See the doc: For block ciphers, the output size will always be less than or
    //equal to the input size plus the size of one block.
    //That's why we need to add the size of one block here
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void* buffer = malloc(bufferSize);
   
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesDecrypted);
   
    if (cryptStatus == kCCSuccess)
    {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSMutableData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }
   
    free(buffer); //free the buffer;
    return nil;
}

@end