Digital Signatures
Using asymmetric cryptography to prove that a message came from a specific signer and was not altered, without sharing a secret.
Proving Origin Without a Shared Secret
A digital signature lets a signer prove authorship of data using a private key that only they hold, while anyone can verify it using the corresponding public key. Unlike a shared-secret tag, no verifier ever learns anything that would let them forge the signer's signature. This gives three guarantees at once: authenticity (who signed), integrity (unaltered since signing), and non-repudiation (the signer cannot plausibly deny it).
How It Works
- The signer hashes the message to a digest
- The digest is transformed with the private key to produce the signature
- A verifier hashes the received message and checks the signature with the public key
- A valid result proves the message is genuine and unchanged
Non-Repudiation
Because only the private-key holder could produce a valid signature, a verified signature is evidence the signer cannot easily disown. This property distinguishes digital signatures from symmetric message authentication codes, where both parties share the key and either could have produced the tag, so neither can prove the other did.
Algorithms and the Quantum Horizon
Classic signature schemes rely on RSA or elliptic curves, which a large quantum computer would break. Post-quantum signature schemes, lattice-based and hash-based, are standardized replacements. Systems that must verify signatures for decades should plan for this migration now.
Fusion Context
Digital signatures let a fusion plant's controllers accept only firmware and software signed by an authorized key, rejecting anything unsigned or tampered. In the Hyperion breeder and burner designs, signing keys are hardware-protected and chosen with post-quantum migration in mind, since the plant's decades-long life exceeds the expected lifetime of today's signature algorithms.