Code signing is widely used to protect software that is distributed over the Internet. Code signing does not alter it; it simply appends a digital signature to the executable code itself. This digital signature provides enough information to authenticate the signer as well as to ensure that a code is not been subsequently modified. Code signing digital IDs (or certificates) allow content publishers including software developers to sign their content that includes software objects, macros, device drivers, firmware images, configuration files or other types of content for secure delivery over the Internet.

Digital signatures are created using a public-key signature algorithm such as the RSA public-key cipher. A public-key algorithm actually uses two different keys: the public key and the private key (called a key pair). The private key is known only to its owner, while the public key can be available to anyone. Public-key algorithms are designed so that if one key is used for encryption, the other is necessary for decryption. Furthermore, the decryption key cannot be reasonably calculated from the encryption key. In digital signatures, the private key generates the signature, and the corresponding public key validates it. 

When customers download software signed with a Code Signing Certificate issued by a trusted Certificate Authority, they can be assured of:

• Content Source: End users can confirm that the software really comes from the publisher who signed it.
• Content Integrity: End users can verify that the software has not been altered or corrupted since it was signed.

Users benefit from this software accountability because they know who published the software and that the code hasn't been tampered with. In the extreme case that software performs unacceptable or malicious activity on their computers; users can also pursue recourse against the publisher. This accountability and potential recourse serve as a strong deterrent to the distribution of harmful code. Developers and Web masters benefit from these Certificates because it builds trust in their names and makes it more difficult to falsify their products. By signing their code, developers build a trusted relationship with users, who learn they can download software signed by that publisher or Web site with confidence. And users can make educated decisions about what software they want to download, knowing who published the software and that it hasn't been tampered with.