Verifying Signed Messages Without a Public Key: Understanding Bitcoin-Qt’s Signature Verification Feature

When sending signed messages on the Bitcoin network using the Bitcoin-Qt software, a common concern arises: how to verify that the message was actually sent by the intended signer without having access to their public key. In this article, we will dive deeper into Bitcoin-Qt’s signature verification feature and explore its features.

What is a signature in Bitcoin?

In Bitcoin, a signature is not actually a “public key” like those used in other cryptographic systems. Rather, it is an algorithmic solution created by the sender that proves ownership of the message. The process involves hashing the message, generating a hash of the sender’s public key, and signing the resulting hash with the private key.

How ​​does Bitcoin-Qt sign messages?

Bitcoin-Qt uses the Elliptic Curve Digital Signature Algorithm (ECDSA) to sign messages. This algorithm is widely used in modern cryptography for its efficiency, scalability, and security. Here is a general overview of how it works:

• Message Preparation: The sender prepares their message by hashing it using Bitcoin-Qt’s “deterministic hash function.” This process creates an input string that will serve as the basis for generating the signature.

• Key Generation: The sender generates a cryptographic key pair, which includes:

• A private key (also called a seed or entry point): This is used to sign messages and verify identities.

• A public key: This is what anyone can use to send a signed message to the sender.

The Signing Process

To create a signature, the sender follows these steps:

• Hash Input: The sender hashes their input message using the deterministic hash function.

• Hash Public Key: The sender hashes their public key using the same algorithm used to sign messages.

• Combine Hash: The sender combines the hashed input and the public key to produce a unique input string, which is then signed with the private key.

Signature Verification in Bitcoin-Qt

To verify that a signed message was actually sent by the intended signer without having access to their public key, Bitcoin-Qt uses a combination of cryptographic techniques:

• Verify Hash: The sender hashes the signature and verifies that it matches the expected hash produced by combining the hashed input and the public key.

• Verify Signature: If the verification is successful, the sender can be confident that the message was signed by the intended signer.

Conclusion

In summary, Bitcoin-Qt’s signature verification feature uses a combination of hashing algorithms and cryptographic keys to ensure the authenticity and integrity of signed messages. By generating a pair of keys (private and public) and using them to sign messages, Bitcoin-Qt provides an efficient and secure way to verify identities and signatures without having to rely on a public key infrastructure.

This feature is particularly useful in scenarios where access to public keys is limited or impossible. However, it is important to note that this approach has its limitations and may not be suitable for all use cases.