(Objective-C) Exporting and Importing Accumulated Entropy

When a system starts, a good established source of entropy may be lacking. The Fortuna algorithm keeps 32 internal entropy pools. When AddEntropy is called, it is added to these internal pools. (The details of the Fortuna algorithm can be read elsewhere.)

This example demonstrates how the entropy that has accumulated within the internal pools can be exported (such as when an application exits) and then imported when an application starts. (It is the application's job to persist the exported entropy to a database, file, etc.)

Importing entropy helps ensure an application is beginning with an adequate source of entropy for random number generation.

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#import <CkoGlobal.h>
#import <CkoPrng.h>
#import <NSString.h>

// All Chilkat classes can be unlocked at once at the beginning of a program
// by calling UnlockBundle.  It requires a Bundle unlock code.
CkoGlobal *chilkatGlob = [[CkoGlobal alloc] init];
BOOL success = [chilkatGlob UnlockBundle: @"Anything for 30-day trial."];
if (success != YES) {
    NSLog(@"%@",chilkatGlob.LastErrorText);
    return;
}

CkoPrng *fortuna = [[CkoPrng alloc] init];

// Generate random data and periodically add entropy...
success = [fortuna AddEntropy: [fortuna GetEntropy: [NSNumber numberWithInt: 32] encoding: @"hex"] encoding: @"hex"];
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
success = [fortuna AddEntropy: [fortuna GetEntropy: [NSNumber numberWithInt: 16] encoding: @"hex"] encoding: @"hex"];
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
success = [fortuna AddEntropy: [fortuna GetEntropy: [NSNumber numberWithInt: 16] encoding: @"hex"] encoding: @"hex"];
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
success = [fortuna AddEntropy: [fortuna GetEntropy: [NSNumber numberWithInt: 16] encoding: @"hex"] encoding: @"hex"];
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);

NSString *exportedEntropy = [fortuna ExportEntropy];
// The application would persist the exported entropy in some way,
// such as to a file, or to a database, etc.

// Create a new PRNG object and initialize the internal entropy pools
// with the previously exported entropy:
CkoPrng *fortuna2 = [[CkoPrng alloc] init];
success = [fortuna2 ImportEntropy: exportedEntropy];

// Generate more random data, continuing to add entropy as we go along..
NSLog(@"%@",[fortuna2 GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna2 GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna2 GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
success = [fortuna2 AddEntropy: [fortuna2 GetEntropy: [NSNumber numberWithInt: 16] encoding: @"hex"] encoding: @"hex"];
NSLog(@"%@",[fortuna2 GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna2 GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
NSLog(@"%@",[fortuna2 GenRandom: [NSNumber numberWithInt: 16] encoding: @"hex"]);
success = [fortuna2 AddEntropy: [fortuna2 GetEntropy: [NSNumber numberWithInt: 16] encoding: @"hex"] encoding: @"hex"];
// ..