Verifying Signed Messages Without a Public Key: Understanding the Bitcoin-Qt Signature Verification Feature
When sending signed messages over the Bitcoin network using the Bitcoin Qt software, a common question arises: How can you verify that the message was actually sent by the intended signer without having access to their public key? In this article, we’ll look at the Bitcoin-Qt signature verification feature and examine how it works.
What is a signature in Bitcoin?
In Bitcoin, a signature is not actually a “public key” like in other cryptographic systems. Instead, it’s 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 then signing the resulting hash with their private key.
How does Bitcoin-Qt sign messages?
Bitcoin-Qt uses the ECDSA (Elliptic Curve Digital Signature Algorithm) algorithm to sign messages. This algorithm is widely used in modern cryptography due to its efficiency, scalability, and security. Here is an 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 is used as the basis for generating the signature.
- Key generation: The sender generates a cryptographic key pair, including:
- A private key (also called a base or entry point): This is used to sign messages and verify identities.
- A public key: With this, anyone can send a signed message back to the sender.
Signing Process
To create a signature, the sender follows these steps:
- Hash Input: The sender hashes their input message using a deterministic hash function.
- Hash Public Key: The sender calculates their public key using the same algorithm used to sign messages.
- Combine Hashes: The sender combines the hashed input and the public key to create a single 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:
- Hash Verification: The sender indexes the signature and checks if it matches the expected hash created by combining the hashed input and the public key.
- Signature Verification: If the verification is successful, the sender can be sure that the message was signed by the intended signer.
Conclusion
In short, the Bitcoin-Qt 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 relying on a public key infrastructure.
This feature is especially useful in scenarios where access to public keys is restricted or not possible. However, it is important to note that this approach has its limitations and may not be suitable for all use cases.