实现与加密一起使用的文件格式 - Cocoa

Question

我需要在我的加密中实现盐，但要这样做，我需要以我需要创建的文件格式存储它，以便我以后可以检索它来解密。在加密方面，我是菜鸟。文件格式的规范应该是这样的：

密文：密文长度； 盐：盐的长度；

然后把密文和盐写出来。这是 xcode 真正让我感到困惑的地方，例如创建新文件等。

我该怎么做？然后取回盐进行解密？

谢谢，非常感谢您的帮助。

Answer 1

您可以考虑像这样使用NSMutableDictionary 和NSKeyedUnarchiver：

// Example ciphertext and salt
NSString *ciphertext = @"the ciphertext";
NSString *salt = @"the salt";

// File destination
NSString *path = @"/Users/Anne/Desktop/Archive.dat";

// Create dictionary with ciphertext and salt
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
[dictionary setObject:ciphertext forKey:@"ciphertext"];
[dictionary setObject:salt forKey:@"salt"];

// Archive dictionary and write to file
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:dictionary];
[data writeToFile:path options:NSDataWritingAtomic error:nil];

// Read file and unarchive
NSMutableDictionary *theDictionary = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

// Get ciphertext and salt
NSString *theCiphertext = [theDictionary objectForKey:@"ciphertext"];
NSString *theSalt = [theDictionary objectForKey:@"salt"];

// Show Result
NSLog(@"Extracted ciphertext: %@",theCiphertext);
NSLog(@"Extracted salt: %@",theSalt);

输出：

Extracted ciphertext: the ciphertext
Extracted salt: the salt

编辑

回复评论：NSData 和 NSString 都具有 length。

快速示例：

NSString *theString = @"Example String";
NSData *theData = [theString dataUsingEncoding:NSUTF8StringEncoding];

NSUInteger stringLength = [theString length];
NSUInteger dataLength = [theData length];

NSLog(@"String length: %ld",stringLength);
NSLog(@"Data length: %ld",dataLength);

输出：

String length: 14
Data length: 14