I got a warning generateIv method in FBEncryptorAES.m

generateIv Method

+ (NSData*)generateIv
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        srand(time(NULL));
    });

    char cIv[FBENCRYPT_BLOCK_SIZE];
    for (int i=0; i < FBENCRYPT_BLOCK_SIZE; i++) {
        cIv[i] = rand() % 256;
    }
    return [NSData dataWithBytes:cIv length:FBENCRYPT_BLOCK_SIZE];
}

The warning...
FBEncryptorAES.m:156:15: Implicit conversion loses integer precision: 'time_t' (aka 'long') to 'unsigned int'