Code signing

Code signing is the practice of applying a digital signature to distributed software — installers, assemblies, updates — so that whoever receives it can verify two things before running it: that it comes from the stated publisher, and that not a byte has changed since it was signed. On Windows the common scheme is Authenticode; operating systems and endpoint controls increasingly refuse or warn on unsigned code.

As a supply-chain control, the signature is only as trustworthy as the custody of the private key. A key that lives on a developer's laptop can be stolen with it, and a signature from a stolen key vouches for malware. That is why mature practice keeps the key in a hardware security module (HSM), makes signing part of the build pipeline rather than a manual step, and treats a signing event as an auditable record. When evaluating a vendor, the question is not whether the binaries are signed but where the key lives and who can invoke it.