Introduction to Privacy Protocols — Ring Signature Explained

QURAS utilizes two privacy technologies: zk-Snarks and Ring Signature. We already explained how zk-Snarks work, and now is the time for Ring Signature.

Ring Signature was developed by Ron Rivest, Adi Shamir, and Yael Tauman, and introduced at ASIACRYPT in 2001. The name, ring signature, comes from the ring-like structure of the signature algorithm.

The concept is similar to the group signatures — there is no proven way to identify the actual signer of a ring signature transaction and the group of users can be included in the ring without any additional setup.

What are Ring Signatures

The original idea behind ring signatures was to be a way to leak secret information, specifically, from high ranking government officials, without actually revealing the person’s identity. Since the appearance of Ring Signatures, various improvements were made to the technology.

For example, Eiichiro Fujisaki and Koutarou Suzuki proposed Traceable Ring Signatures in 2006 as an improvement that would counter some vulnerabilities around ring signatures regarding manipulation by malicious or irresponsible signers. The improved version is now used in some privacy coins, which provides untraceability of the sender in a P2P transaction by obscuring the source of the inputs.

Ring Confidential Transactions (Ring CT) was also innovation, and Monero Research Labs applied it in 2015. It extended the anonymity capabilities of the original ring signature by hiding the actual transaction amounts between a sender and recipient in addition to obfuscating the identity of the sender.

Ring signatures are an advanced scheme that goes past typical digital signatures used in other cryptocurrencies such as ECDSA or Schnorr signatures. It may require multiple public keys for verification and the word “ring” is used to describe the group of partial digital signatures from different users used to form a unique signature that is used to sign a transaction. This helps keep the actual signer anonymous.

The structure of a ring signature basically works as follows:

• Maria wants to send Kenny 10 coins, so she initiates a transaction through her wallet to Kenny.
• Maria’s digital signature for this transaction is a one-time spend key that starts with output being spent from her wallet.
• The non-signers of the ring signature are past transaction outputs that are arbitrarily picked from the blockchain and act as decoys in the transaction.
• All ring members are plausible signers of the transaction, and it is computationally infeasible for a third party to detect the actual signer.
• All of the outputs of the ring signature together make up the input of the transaction.
• The creator of the transaction (Maria) is provably eligible to spend the specified transaction amount without distinguishing her identity from the others in the ring.
• Although Maria’s public key is used in her own transaction, it may be arbitrarily used in other transactions in the coin’s network as a muddling factor.
• Further, the automatic creation of unique one-time keys prevents transaction linkability and is made possible through an optimization of the Diffie-Hellman key exchange.

Ring Confidential Transactions (Ring CT)

As mentioned above, the Ring CT was developed to add privacy to both the sender and recipient through obfuscating the amount being sent. This is an essential improvement of the original technology. Transactions with Ring CT no longer need to be included in the rings of the same size outputs, but can arbitrarily select members from any output size.

Simply put — outside observers cannot see the transaction but can be assured through cryptographic verification that the transaction is valid.

Ring Signatures are a vital component of many privacy-focused cryptocurrencies (including QURAS) and should become more relevant moving forward.

Conclusion

There are a lot of components when it comes to creating and maintaining a cryptocurrency that provides users with full anonymity. Ring Signatures and their optimization Ring CT are a great invention, and it will be exciting to watch it develop further in the coming years.