Objective-c中的AES256解密问题

Question

我正在尝试使用以下代码段解密文件,该文件使用32字节密钥加密.因此,当我尝试加密文件数据时,一切正常.但是当我尝试解密时,程序甚至不会if (cryptStatus == kCCSuccess)在CryptoExtensions.m中传递条件.我真的很累,想出一个问题.我试图使用Base64解码,但我的文件以UTF8编码保存,所以当我把它的内容放在NSData的日志中时我没有问题:

NSData *fileData = [[[NSData alloc] initWithContentsOfFile:destPath] autorelease];

NSLog(@"File data:%@",[[NSString alloc] initWithData:fileData encoding:NSUTF8StringEncoding]);

但是当我试图解密它时,我nil从CryptoExtensions方法获得:

NSData *aesResponse = [fileData AES256DecryptWithKey:@"4QXcCZlgRAIchiaqkMVpF3nkpARmdL3z"];
NSLog(@"AES:%@",[[NSString alloc] initWithData:aesResponse encoding:NSUTF8StringEncoding]);

这是crypto片段的内容:

CryptoExtensions.h

#import <Foundation/Foundation.h>
@interface NSData (CryptoExtensions)
- (NSData*)AES256EncryptWithKey:(NSString*)key;
- (NSData*)AES256DecryptWithKey:(NSString*)key;
@end

CryptoExtensions.m

#import "CryptoExtensions.h"
#import <CommonCrypto/CommonCryptor.h>
@implementation NSData (CryptoExtensions)
- (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 [NSData 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 [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }

    free(buffer); //free the buffer;
    return nil;
}
@end

Answer 1

此代码存在重大安全问题.它错误地构造了AES密钥,大大减少了密钥空间并且没有IV,从而为第一个块创建了问题.我强烈建议不要使用此代码.

通过开发这个常用代码片段的替代品,我已经完成了大部分工作.请参阅https://github.com/rnapier/RNCryptor.如果它对您不起作用,请告诉我.我试图让它足够容易用于人们将停止使用的所有常见情况AES256EncryptWithKey.

有关此代码问题的更长时间的讨论,请参阅使用CommonCrypto使用AES正确加密.我喜欢有人将AES加密包装成一个易于使用的类别.我只是希望它没有那么多安全问题.

编辑:回到你的实际问题,你是否用它AES256EncryptWithKey来加密这些数据？如果没有,则具体格式可能完全不同.几乎每个AES加密实现都使用不同的方法来生成其输入参数,然后生成其输出(大多数都不能很好地记录这一点).您必须匹配参数和格式.例如,您不能使用AES256EncryptWithKey解密生成的内容openssl enc.