The determineWinner function of a smart contract implementation for HashHeroes Tiles, an Ethereum game, uses a certain blockhash value in an attempt to generate a random number for the case where NUM_TILES equals the number of people who purchased a tile, which allows an attacker to control the awarding of the prize by being the last person to purchase a tile.
Weakness
The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Hashheroes |
Hashheroes |
- (including) |
- (including) |
Potential Mitigations
- Use a well-vetted algorithm that is currently considered to be strong by experts in the field, and select well-tested implementations with adequate length seeds.
- In general, if a pseudo-random number generator is not advertised as being cryptographically secure, then it is probably a statistical PRNG and should not be used in security-sensitive contexts.
- Pseudo-random number generators can produce predictable numbers if the generator is known and the seed can be guessed. A 256-bit seed is a good starting point for producing a “random enough” number.
References