This paper presents randomized protocols for signing contracts, certified mail, and flipping a coin, all based on a 1-out-of-2 oblivious transfer subprotocol. The 1-out-of-2 oblivious transfer allows one party to transfer exactly one secret out of two recognizable secrets to another party, with the recipient receiving either secret with equal probability, and the sender being unaware of which secret was received. The paper defines and implements this subprotocol using any public key cryptosystem. The main contributions include: 1. **Contract Signing Protocol**: A protocol that ensures viability and approximate concurrency. Each party can instantly present their counterpart's signature to the contract, and with high probability, both parties can compute each other's signatures using similar computational effort. 2. **Certified Mail Protocol**: A protocol that reduces the problem of sending certified mail to an exchange of keys and receipts. The receiver gets the mail if and only if they receive a receipt that certifies the mail was sent. 3. **Coin Flipping Protocol**: A protocol that ensures both parties know the outcome of the coin flip simultaneously and cannot be influenced by the other party. The paper also discusses the implementation of the 1-out-of-2 oblivious transfer using any public key cryptosystem and provides a detailed analysis of the subprotocol's properties, including its security and efficiency.This paper presents randomized protocols for signing contracts, certified mail, and flipping a coin, all based on a 1-out-of-2 oblivious transfer subprotocol. The 1-out-of-2 oblivious transfer allows one party to transfer exactly one secret out of two recognizable secrets to another party, with the recipient receiving either secret with equal probability, and the sender being unaware of which secret was received. The paper defines and implements this subprotocol using any public key cryptosystem. The main contributions include: 1. **Contract Signing Protocol**: A protocol that ensures viability and approximate concurrency. Each party can instantly present their counterpart's signature to the contract, and with high probability, both parties can compute each other's signatures using similar computational effort. 2. **Certified Mail Protocol**: A protocol that reduces the problem of sending certified mail to an exchange of keys and receipts. The receiver gets the mail if and only if they receive a receipt that certifies the mail was sent. 3. **Coin Flipping Protocol**: A protocol that ensures both parties know the outcome of the coin flip simultaneously and cannot be influenced by the other party. The paper also discusses the implementation of the 1-out-of-2 oblivious transfer using any public key cryptosystem and provides a detailed analysis of the subprotocol's properties, including its security and efficiency.