What is the approved method of getting a random number in macOS in Objective C? Presently I'm using:
srandomdev();
randomDevice = fopen("/dev/random", "r");
//
//
//
-(uint64)random64
{
uint64_t value = 0;
int i;
for (i = 0 ; i < sizeof(value); i++)
{
value <<= 8;
value |= fgetc(randomDevice);
}
return value;
}
However, this method no longer appears in the documentation. Is there a more modern implementation?
I found the docs I needed: [https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc). The core foundation security services api contains the appropriate system call. The modern implementation of the above would be:
-(uint64)random64
{
uint64_t value = 0;
uint8 randomByte;
int i, err;
for (i = 0 ; i < sizeof(value); i++)
{
value <<= 8;
err = SecRandomCopyBytes( kSecRandomDefault , 1 , &randomByte );
value |= randomByte;
}
return value;
}
Check out the arc4random_uniform function.
uint32_t randomNumber = arc4random_uniform(25);
I found the docs I needed: [https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc). The core foundation security services api contains the appropriate system call. The modern implementation of the above would be:
-(uint64)random64
{
uint64_t value = 0;
uint8 randomByte;
int i, err;
for (i = 0 ; i < sizeof(value); i++)
{
value <<= 8;
err = SecRandomCopyBytes( kSecRandomDefault , 1 , &randomByte );
value |= randomByte;
}
return value;
}
There’s two cases here:
Cryptographically sound random numbers
Pseudo random numbers
It sounds like you want the former, in which case I agree that SecRandomCopyBytes is a good option. However, you can get all eight bytes at once:
- (uint64)random64 {
uint64_t result;
OSStatus err = SecRandomCopyBytes(kSecRandomDefault, sizeof(result), &result);
assert(err == errSecSuccess);
return result;
}
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