Root + Impact

Description

The PizzaDrop contract uses predictable timestamp-based pseudo-randomness for reward generation instead of cryptographically secure randomness. The get_random_slice() function on line 90-92 generates reward amounts using timestamp::now_microseconds() % 401 + 100, making all rewards completely deterministic and exploitable.

Since blockchain timestamps are publicly visible and predictable, attackers can calculate optimal transaction timing to guarantee maximum rewards (500 Octas) while legitimate users receive suboptimal amounts based on random registration timing.

Risk

Likelihood:

• Every user registration automatically triggers this predictable generation mechanism

• Every user registration automatically triggers this predictable generation mechanism

• Sophisticated attackers can time transactions to microsecond precision using MEV techniques

• No additional conditions or privileges required for exploitation

Impact:

• Unfair reward distribution heavily favoring attackers who optimize transaction timing

• Legitimate users systematically receive suboptimal rewards due to random timing

• Complete breakdown of airdrop fairness guarantees and randomness assumptions

• Potential for coordinated attacks to drain maximum value from the reward pool

• Reputational damage to protocol due to manipulated reward distribution

Proof of Concept

Live blockchain testing demonstrates complete predictability of the randomness mechanism:

An attacker monitoring blockchain state can calculate that registering when timestamp % 401 = 300 guarantees the maximum reward of 400 + 100 = 500 Octas, while other users receive random amounts based purely on timing luck.

Recommended Mitigation

Implement cryptographically secure randomness or combine multiple unpredictable entropy sources to prevent timing-based manipulation of reward amounts.