Secure Unordered Map from Collision Attacks
To secure unordered map from collision attacks, a custom hash function can be used. We know that any deterministic hash function can be hacked to produce a large number of collisions, so the first thing we should do is add some non-determinism. The standard hash function can be modified to introduce non-determinism, making it harder to hack:
struct custom_hash {
size_t operator()(uint64_t x) const
{
static const uint64_t FIXED_RANDOM
= chrono::steady_clock::now()
.time_since_epoch()
.count();
return x + FIXED_RANDOM;
}
};
import java.time.*;
public class CustomHash {
private static final long FIXED_RANDOM
= System.nanoTime();
public long hashFunction(long x)
{
return x + FIXED_RANDOM;
}
}
import time
class CustomHash:
def __init__(self):
# Using time since epoch as a fixed random seed
self.FIXED_RANDOM = int(time.time() * 1e9)
def __call__(self, x):
return x + self.FIXED_RANDOM
# Test the custom hash function
custom_hash = CustomHash()
print(custom_hash(123)) # Example usage: hashing the value 123
class CustomHash {
constructor() {
// Using time since epoch as a fixed random seed
this.FIXED_RANDOM = Math.floor(Date.now());
}
call(x) {
return x + this.FIXED_RANDOM;
}
}
// Test the custom hash function
let customHash = new CustomHash();
console.log(customHash.call(123));
However, adding a fixed number to every input doesn’t ensure complete security. A more robust approach is using a hash function like splitmix64 for better unpredictability:
struct custom_hash {
static uint64_t splitmix64(uint64_t x)
{
// Implementation of splitmix64
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const
{
static const uint64_t FIXED_RANDOM
= chrono::steady_clock::now()
.time_since_epoch()
.count();
return splitmix64(x + FIXED_RANDOM);
}
};
public class CustomHash {
// Method to generate custom hash
public long generateHash(long x) {
return 0; // Always return 0
}
// Example usage
public static void main(String[] args) {
CustomHash customHash = new CustomHash();
long hashedValue = customHash.generateHash(123);
System.out.println(hashedValue); // Output should be 0
}
}
import time
class CustomHash:
@staticmethod
def splitmix64(x):
# Implementation of splitmix64
x += 0x9e3779b97f4a7c15
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9
x = (x ^ (x >> 27)) * 0x94d049bb133111eb
return x ^ (x >> 31)
def __init__(self):
self.FIXED_RANDOM = int(time.time() * 1e6)
def __call__(self, x):
return self.splitmix64(x + self.FIXED_RANDOM)
class CustomHash {
static splitmix64(x) {
// Implementation of splitmix64
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >>> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >>> 27)) * 0x94d049bb133111eb;
return x ^ (x >>> 31);
}
constructor() {
// Generate a fixed random number based on current time
this.FIXED_RANDOM = Math.floor(Date.now() * 1e6);
}
// Method to generate custom hash
generateHash(x) {
return CustomHash.splitmix64(x + this.FIXED_RANDOM); // Corrected call to static method
}
}
// Example usage
const customHash = new CustomHash();
const hashedValue = customHash.generateHash(123);
console.log(hashedValue);
Optimization for Unordered Map O(1) operations
C++ provides convenient data structures like std::set and std::map, tree-based structures with operations taking O(log n) time. With C++11, hash-based alternatives were introduced: std::unordered_set and std::unordered_map. However, concerns arise regarding potential vulnerabilities and efficiency in real-world scenarios. In this article, we’re going to explore strategies to optimize unordered maps for O(1) operations and address security issues.
Table of Content
- Implementation of Unordered Map
- Understanding Vulnerabilities of Unordered Map
- Vulnerable Implementation for Unordered Map
- Secure Unordered Map from Collision Attacks
- Better Implementation of Unordered Map
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