I have previously written a number of articles on Cryptography in .NET, like the following :
Part 1 – Advanced Encryption Standard (AES)
Part 2 – RSA
Part 3 – Random Numbers and Hashes
Part 4 – Hybrid Encryption Protocols
Block Encrypter .NET Library for secure AES Encryption
In this article I will show you how to create and use Digital Signatures in .NET.
A digital signature is a mathematical scheme that demonstrates the authenticity of a message or document. A valid digital signature gives the recipient reason to believe that the message was created by a known sender, such that the sender cannot deny having sent the message (authentication and non-repudiation) and that the message was not altered in transit (integrity). Digital signatures are commonly used for software distribution, financial transactions, and in other cases where it is important to detect forgery or tampering.
Digital signatures are often used to implement a digital analog to hand written signatures. In broader terms this refers to any electronic data that carries the intent of a signature. Digital signatures employ a type of asymmetric cryptography. For messages sent through a non-secure channel, a properly implemented digital signature gives the receiver reason to believe the message was sent by the claimed sender. Digital signatures are equivalent to traditional handwritten signatures in many respects, but properly implemented digital signatures are more difficult to forge than the handwritten type. Digital signature schemes, in the sense used here, are cryptographic based, and must be implemented properly to be effective. Digital signatures can also provide non-repudiation, meaning that the signer cannot successfully claim they did not sign a message, while also claiming their private key remains secret.
Example Digital Signature Flow
A digital signature scheme consists of three algorithms
- A key generation algorithm that generates a private and public key, such as RSA.
- A signing algorithm that, given a message and a private key, produces a signature.
- A signature verifying algorithm that, given a message, public key and a signature, either accepts or rejects the message’s claim to authenticity.
Two main properties are required. First, the authenticity of a signature generated from a fixed message and fixed private key can be verified by using the corresponding public key. Secondly, it should be computationally infeasible to generate a valid signature for a party without knowing that party’s private key. A digital signature is an authentication mechanism that enables the creator of the message to attach a code that act as a signature. It is formed by taking the hash of message and encrypting the message with creator’s private key.