如何在iOS中实现Blowfish算法

Question

在iOS中实现BlowFish ECB加密的最佳方法是什么？我一直在谷歌上搜索,在这里找到了图书馆.但是没有这个库的文档.不知道如何使用它.

Answer 1

我从Bruce Schneier的网站上获得了Paul Kocher的实现.以下是加密方法的外观:

#define PADDING_PHRASE @"       "

#import "CryptoUtilities.h"
#import "blowfish.h"
#import "NSData+Base64Utilities.h"

@implementation CryptoUtilities

+ (NSString *)blowfishEncrypt:(NSData *)messageData usingKey:(NSData *)secretKey
{
    NSMutableData *dataToEncrypt = [messageData mutableCopy];

    if ([dataToEncrypt length] % 8) {
        NSMutableData *emptyData = [[PADDING_PHRASE dataUsingEncoding:NSUTF8StringEncoding] mutableCopy];

        emptyData.length = 8 - [dataToEncrypt length] % 8;
        [dataToEncrypt appendData:emptyData];
    }

    // Here we have data ready to encipher    
    BLOWFISH_CTX ctx;
    Blowfish_Init (&ctx, (unsigned char*)[secretKey bytes], [secretKey length]);

    NSRange aLeftRange, aRightRange;
    NSData *aLeftBox, *aRightBox;
    unsigned long dl = 0, dr = 0;

    for (int i = 0; i < [dataToEncrypt length]; i += 8) { // Divide data into octets...
        // …and then into quartets
        aLeftRange = NSMakeRange(i, 4);
        aRightRange = NSMakeRange(i + 4, 4);

        aLeftBox = [dataToEncrypt subdataWithRange:aLeftRange];
        aRightBox = [dataToEncrypt subdataWithRange:aRightRange];

        // Convert bytes into unsigned long
        [aLeftBox getBytes:&dl length:sizeof(unsigned long)];
        [aRightBox getBytes:&dr length:sizeof(unsigned long)];

        // Encipher
        Blowfish_Encrypt(&ctx, &dl, &dr);

        // Put bytes back
        [dataToEncrypt replaceBytesInRange:aLeftRange withBytes:&dl];
        [dataToEncrypt replaceBytesInRange:aRightRange withBytes:&dr];
    }

    return [dataToEncrypt getBase64String];
}

我不是很擅长C,但似乎我的实现工作正常.解密你只需要重复相同的步骤,但不是Blowfish_Encrypt你需要调用Blowfish_Decrypt.
这是一个源代码(我假设您只是解密密文,但不在这里处理填充):

+ (NSData *)blowfishDecrypt:(NSData *)messageData usingKey:(NSData *)secretKeyData
{
    NSMutableData *decryptedData = [messageData mutableCopy];

    BLOWFISH_CTX ctx;
    Blowfish_Init (&ctx, (unsigned char*)[secretKeyData bytes], [secretKeyData length]);

    NSRange aLeftRange, aRightRange;
    NSData *aLeftBox, *aRightBox;
    unsigned long dl = 0, dr = 0;

    for (int i = 0; i< [decryptedData length]; i += 8) { // Divide data into octets...
        // …and then into quartets
        aLeftRange = NSMakeRange(i, 4);
        aRightRange = NSMakeRange(i + 4, 4);

        aLeftBox = [decryptedData subdataWithRange:aLeftRange];
        aRightBox = [decryptedData subdataWithRange:aRightRange];

        // Convert bytes into unsigned long
        [aLeftBox getBytes:&dl length:sizeof(unsigned long)];
        [aRightBox getBytes:&dr length:sizeof(unsigned long)];

        // Decipher
        Blowfish_Decrypt(&ctx, &dl, &dr);

        // Put bytes back
        [decryptedData replaceBytesInRange:aLeftRange withBytes:&dl];
        [decryptedData replaceBytesInRange:aRightRange withBytes:&dr];
    }

    return decryptedData;
}

您可能希望返回纯字节或Base64字符串.对于最后一种情况,我有一个类别,它添加了一个初始化器,它使用Base64字符串和一个方法初始化NSData对象,该方法允许从NSData获取Base64字符串.

您还应该考虑使用PADDING_PHRASE,例如,如果您不仅要添加几个空格,而是添加一些随机字节,该怎么办？在这种情况下,您应该以某种方式发送填充长度.

更新:实际上,您不应在进程中使用PADDING_PRASE.相反,您应该使用Wikipedia页面上描述的块密码的标准算法之一