The paper introduces the concept of untraceable electronic cash, addressing the privacy issues associated with credit cards and paper cash. The authors propose a method for generating and using electronic coins that are untraceable to the bank, ensuring that the bank cannot link specific coins to individual users. The scheme uses RSA digital signatures and a one-way function to create and verify electronic coins. Key features include: 1. **Untraceability**: The bank cannot link specific coins to individual users, protecting privacy. 2. **On-line Clearing**: While expensive, this method ensures that each transaction is verified by the bank. 3. **Security Against Collusion**: The scheme includes measures to prevent collusion between users and shopkeepers, such as fixed query strings and random challenges. 4. **Proving Multiple Spending**: The bank can detect and prevent users from reusing the same coin multiple times, using digital signatures and certified public keys. 5. **Untraceable Checks**: A variant of the scheme allows users to request checks with guaranteed refunds, ensuring that the bank does not know the exact amounts spent. 6. **Blacklisting Withdrawals**: The bank can blacklist coins used more than once, enhancing security. The paper also discusses the practical implementation of these schemes, including the use of cut-and-choose methodology and the importance of secure one-way functions. The authors acknowledge the contributions of Russell Impagliazzo and Eugene van Heigst, and highlight ongoing research in formal proofs and security reductions.The paper introduces the concept of untraceable electronic cash, addressing the privacy issues associated with credit cards and paper cash. The authors propose a method for generating and using electronic coins that are untraceable to the bank, ensuring that the bank cannot link specific coins to individual users. The scheme uses RSA digital signatures and a one-way function to create and verify electronic coins. Key features include: 1. **Untraceability**: The bank cannot link specific coins to individual users, protecting privacy. 2. **On-line Clearing**: While expensive, this method ensures that each transaction is verified by the bank. 3. **Security Against Collusion**: The scheme includes measures to prevent collusion between users and shopkeepers, such as fixed query strings and random challenges. 4. **Proving Multiple Spending**: The bank can detect and prevent users from reusing the same coin multiple times, using digital signatures and certified public keys. 5. **Untraceable Checks**: A variant of the scheme allows users to request checks with guaranteed refunds, ensuring that the bank does not know the exact amounts spent. 6. **Blacklisting Withdrawals**: The bank can blacklist coins used more than once, enhancing security. The paper also discusses the practical implementation of these schemes, including the use of cut-and-choose methodology and the importance of secure one-way functions. The authors acknowledge the contributions of Russell Impagliazzo and Eugene van Heigst, and highlight ongoing research in formal proofs and security reductions.