Digital Signature

A digital signature is the result of a mathematical computation. It is similar to a hash value (such as MD5), but there is one important difference: A digital signature relies on a private/public key scheme. Thus, one key (typically the private key) is used to generate the signature, and the other one is used to verify it. This differs from a hash, which is the result of a simple mathematical function, where the same function is used for both generation and verification.

This is a very important difference. With a digital signature verification scheme, both the algorithm and public key can be known and open, but this still does not allow a potential attacker to create a signature for a modified document.

Applications

There are various applications for digital signatures in embedded systems and other places. One simple example is the signing of a document.

Alice can make her public key known to the world, and anybody can now verify that a document claiming to be signed by Alice actually was. The only thing an individual has to ensure is that they have the proper public key (used for verification). SEGGER supplies a free tool based on emSecure for exactly this purpose: Sign&Verify.

Use in embedded systems

In embedded systems, digital signatures can be used for various purposes, such as:

• Firmware updates—for authentication of an update's source.
• Copy (clone) protection— with signature storage for every system device based on the unique ID of a chip in the system. If firmware is copied (cloned) and the signature does not match, the firmware will not function.

Algorithms used

• RSA
• Elliptic curves

Software libraries

One software library that allows generation of keys and signatures as well as verification of signatures in any system (including embedded systems) is SEGGER's emSecure