The most common use of code signing is to provide security when deploying; in some programming languages, it can also be used to help prevent namespace conflicts.
For example, in the case of .NET, the developer uses a private key to sign their libraries or executables each time they build.
This form of code signing is not used on Linux because of that platform's decentralized nature, the package manager being the predominant mode of distribution for all forms of software (not just updates and patches), as well as the open-source model allowing direct inspection of the source code if desired.
This does not ensure that the code itself can be trusted, only that it comes from the stated source (or more explicitly, from a particular private key).
In addition to validation requirements specific to EV, the EV code signing guidelines stipulate that "the Subscriber's private key is generated, stored and used in a crypto module that meets or exceeds the requirements of FIPS 140-2 level 2.
In this scenario, the user would normally have to obtain the public key in some fashion directly from the developer to verify the object is from them for the first time.
Some software frameworks and OSs that check the code's signature before executing will allow you to choose to trust that developer from that point on after the first run.
An application developer can provide a similar system by including the public keys with the installer.
The key can then be used to ensure that any subsequent objects that need to run, such as upgrades, plugins, or another application, are all verified as coming from that same developer.
Sometimes, sandbox systems do not accept certificates, because of a false time-stamp or because of an excess usage of RAM.
For .NET (managed) code, there is an additional mechanism called Strong Name Signing that uses Public/Private keys and SHA-1 hash as opposed to certificates.
[17] The Code Signing Working Group of the CA/Browser Forum decided that starting June 1, 2023, all code signing certificates (not only the EA ones) should mandate private key storage on a physical media, such as in a hardware crypto module conforming to at least FIPS 140-2 Level 2 or Common Criteria EAL 4+.
[19][20][21][22][23][24][25] In the context of consumer devices such as games consoles, the term "unsigned code" is often used to refer to an application which has not been signed with the cryptographic key normally required for software to be accepted and executed.
There are several methods to get unsigned code to execute which include software exploits, the use of a modchip, a technique known as the swap trick or running a softmod.