A few people can deny the importance of electronic signature, since electronic documents are a major part of a modern business. It is important that companies using electronic documents have suitable security mechanisms to protect their documents and to ensure trust and confidence with their business practices. In this respect the electronic signature is an important security component that can be used to protect information and provide trust in electronic business.
The European Directive on a community framework for Electronic Signatures defines an electronic signature as: "Data in electronic form which is attached to or logically associated with other electronic data and which serves as a method of authentication".
Wikipedia, the free encyclopedia, defines an electronic (or digital, which is the same in our context) signature as follows (http://en.wikipedia.org/wiki/Digital_signature):
A digital signature or digital signature scheme is a mathematical scheme for demonstrating the authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, and that it was not altered in transit. Digital signatures are commonly used for software distribution, financial transactions, and in other cases where it is important to detect forgery and tampering.
First attempts to provide mechanism of digitally signed documents was made in early 80-s, but the first commercial software package to offer digital signature was Lotus Notes 1.0, released in 1989, which used the RSA algorithm.
RSA (which stands for Rivest, Shamir and Adleman, who first publicly described it) is an algorithm for public-key cryptography. It is the first algorithm known to be suitable for signing as well as encryption, and was one of the first great advances in public key cryptography.
In our days the most popular document format, providing mechanism of electronic signature, is PDF (Portable Document Format) that enables users to exchange and view electronic documents easily and reliably, independent of the environment in which they were created or the environment in which they are viewed or printed.
The International Organization for Standardization has published new standard ISO 32000-1 in 2008, and it identifies the ways in which an electronic signature, in the form of a digital signature, may be incorporated into a PDF document to authenticate the identity of the author and validate integrity of the document's content.
These signatures are based on the same CMS (Cryptographic Message Syntax) technology and techniques as TS 101 733 (CAdES), but without the extended signature capabilities of CAdES. (Note: CAdES, witch stands for CMS Advanced Electronic Signatures, describes the usage of electronic signature in any generic file or e-mail message, while PAdES, the issue of this article, deals strictly with PDF documents.)