## 2 State-of-the-Art
### Reward Systems with Monetary Value
Four types of collaterals are discussed for stablecoins, each with its own strong points and weak points. Fiat-collateralized stablecoins are pegged to fiat currency and are centralized, which contradicts decentralization principles. Crypto-collateralized stablecoins are pegged to other cryptocurrencies and are often over-collateralized due to volatility. Commodity-collateralized stablecoins are pegged to commodities like gold or oil and are centralized in a similar way to fiat-collateralized stablecoins. Non-collateralized stablecoinshave no backing assets and use algorithms to adjust supply based on demand to stabilize the price. The solution proposed in [41] is a dual-deposit escrow smart contract that ensures cheat-proof delivery and payment for digital goods without third-party intervention. Necessary assumptions include the following: (1) the product can be secured with a digital key, (2) the buyer can verify the product using a pre-known hash value, (3) both parties have asymmetric key pairs known to each other, and (4) transaction fees for deploying and interacting with the smart contract are negligible. The purpose of this solution is to secure transactions by guaranteeing that both the buyer and the seller fulfill their obligations. Building on the previous idea, the system presented in [42] uses a smart contract to act as an escrow, holding the buyer's payment until the trade is completed. Disputes are handled by having parties wager on their honesty, with an arbiter deciding the outcome. The contract requires both parties to place a deposit (wager) that is refunded if they behave honestly. An interesting concept is that there is both a penalty and a reward system. They are computed based on the wager size and a repayment constant. The contract's security is analyzed using game theory, proving that it ensures honest behavior if the arbiter is biased towards honesty. The contract achieves strong game-theoretic security if the penalties for dishonesty are sufficiently high, making deviation from honesty unprofitable. In [43], the author explains how a cryptocurrency should be designed to be valuable. Some guidelines are provided, which must be followed before and after the creation of the currency. Pre-creation guidelines include the following: defining the purpose of issuance, determining desirable behaviors and appropriate rewards, establishing measures to prevent undesirable behaviors such as hacking and spam attacks, and deciding on the block generation cycle along with the amount of cryptocurrency to be issued. Post-creation guidelines include maintaining scarcity by controlling total issuance. They also involve creating continuous market demand and balancing these methods to stabilize or increase cryptocurrency value. An example of how value can be created for a cryptocurrency is found in [44]. Cyclists earn cycle tokens by cycling, with the tokens calculated based on the plausibility and distance of the ride. The real-world value of these tokens is derived from the economic, health, and ecological benefits associated with cycling. A marketplace is established where cycle tokens can be exchanged for various incentives, such as discounts or spare parts. The number of tokens generated corresponds to the square root of the kilometers cycled, with a cap on the maximum number of tokens that can be earned per track and per day. This example highlights the importance of aligning cryptocurrency incentives with real-world benefits. It also emphasizes controlling token supply and providing practical uses. These measures ensure cryptocurrency sustainability and value.