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Code signing: proving who shipped a binary, and what it can't prove
The same use case told visually, ready to present. Speaker notes carry the full explanation.
Software Integrity
Code signing
Proving who shipped a binary, and what that proof can't tell you
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today1 / 8
Incidents
The cryptography worked every time
Stolen keys, a hijacked updater, a poisoned build: control failed, not crypto
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today2 / 8
Mechanics
Hash, sign, timestamp, ship
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today3 / 8
Size
Signature size depends on the key, not the file
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today4 / 8
Timestamps
A signature can outlive its certificate
The verifier asks: was the certificate valid at the timestamped moment?
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today5 / 8
Revocation
Revoke from the moment of compromise
Past releases keep working; anything signed after the leak doesn't
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today6 / 8
Hardware
Signing keys now have to live in hardware
Hardware stops copying the key, not misusing it
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today7 / 8
Keyless
Sigstore: no long-lived key to steal
Trust moves to the identity provider, the CA and the transparency log
Code signing: proving who shipped a binary, and what it can't prove · Classical Crypto Today8 / 8
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