# 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, unlike a hash which is a simple mathematical function result, 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 Signature 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 they have 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.

## In Embedded Systems

In Embedded Systems, Digital Signatures can be used for various purposes, such as

- Firmware updates - Authenticate the source of the firmware update
- Copy (clone) protection - Using the unique ID of a chip in the system, every device will store a signature based on this unique ID. When copied (cloned), if the signature does not match, the firmware will refuse to function.

## Algorithms used

- RSA
- Elliptic curves

## Software libraries

One software library that allows generation of keys as well as signature and verification of signatures in any system including Embedded Systems is SEGGER's emSecure