This paper presents new protocols for fair exchange between two parties using a semi-trusted third party. The goal is to ensure that neither party can gain an advantage by quitting prematurely or misbehaving. The third party is semi-trusted, meaning it may act maliciously on its own but will not collude with either of the main parties. The protocols ensure that no party can gain useful information about the exchanged documents, even if one of the three parties is malicious. The protocols are efficient and can be based on various cryptographic assumptions, such as factoring, discrete logarithms, or graph isomorphism. The fair exchange protocol ensures that both parties receive the documents they are exchanging only if the other party does so. The protocol uses a one-way function to ensure that the documents are consistent with the known hash values. This provides stronger guarantees than existing systems, such as NetBill, which only detect worthless documents after the exchange. The paper describes a basic fair exchange protocol and an optimized version. The basic protocol involves sharing secret keys between two parties using a 2-out-of-2 verifiable secret sharing scheme. The optimized protocol reduces the number of messages and uses encryption and hashing to ensure security. The protocol is efficient, requiring only four messages in the case of no disruptions. The paper also discusses variations of the protocol, including the use of "kindness of strangers" to select a third party at random, and methods to prevent linkability of exchanges. It also addresses applications of the protocol to electronic payment schemes, where fair exchange ensures that a customer receives a document only if the vendor receives payment, and vice versa. The paper concludes that the proposed protocols provide efficient and secure solutions for fair exchange in the semi-trusted third-party setting, with applications to electronic payment schemes. It also suggests that further research is needed to explore other models and applications of fair exchange.This paper presents new protocols for fair exchange between two parties using a semi-trusted third party. The goal is to ensure that neither party can gain an advantage by quitting prematurely or misbehaving. The third party is semi-trusted, meaning it may act maliciously on its own but will not collude with either of the main parties. The protocols ensure that no party can gain useful information about the exchanged documents, even if one of the three parties is malicious. The protocols are efficient and can be based on various cryptographic assumptions, such as factoring, discrete logarithms, or graph isomorphism. The fair exchange protocol ensures that both parties receive the documents they are exchanging only if the other party does so. The protocol uses a one-way function to ensure that the documents are consistent with the known hash values. This provides stronger guarantees than existing systems, such as NetBill, which only detect worthless documents after the exchange. The paper describes a basic fair exchange protocol and an optimized version. The basic protocol involves sharing secret keys between two parties using a 2-out-of-2 verifiable secret sharing scheme. The optimized protocol reduces the number of messages and uses encryption and hashing to ensure security. The protocol is efficient, requiring only four messages in the case of no disruptions. The paper also discusses variations of the protocol, including the use of "kindness of strangers" to select a third party at random, and methods to prevent linkability of exchanges. It also addresses applications of the protocol to electronic payment schemes, where fair exchange ensures that a customer receives a document only if the vendor receives payment, and vice versa. The paper concludes that the proposed protocols provide efficient and secure solutions for fair exchange in the semi-trusted third-party setting, with applications to electronic payment schemes. It also suggests that further research is needed to explore other models and applications of fair exchange.