Understanding Digital Signing with Asymmetric Keys

Introduction

Digital signing is a process that ensures the integrity and authenticity of digital messages or documents. It's like a virtual fingerprint or a sealed envelope in the digital world. This process uses a pair of keys known as asymmetric keys, which include a public key and a private key. In this post, we'll explore the concept of digital signing through an easy-to-understand example.

What are Asymmetric Keys?

Before diving into digital signing, it's essential to understand asymmetric keys. In asymmetric cryptography, two keys are used:

• Private Key: Known only to the owner, used to sign documents.
• Public Key: Shared with others, used to verify signatures made with the private key.

These keys are mathematically related, yet deriving the private key from the public key is practically impossible.

How Does Digital Signing Work?

Digital signing involves creating a digital signature using the sender's private key and then verifying the signature with the sender's public key. Here's a step-by-step breakdown:

1. Creation of a Digital Signature:

   • The sender has a document they want to send securely.
   • The document's hash (a fixed-size string of bits) is created using a hash function. This ensures any change in the document will result in a different hash.
   • The hash is then encrypted with the sender's private key, creating the digital signature.

2. Verification of the Digital Signature:

   • The receiver gets the document along with its digital signature.
   • They decrypt the digital signature using the sender's public key, revealing its hash value.
   • The receiver generates a new hash value from the received document.
   • The document is authentic and unchanged if the new hash matches the decrypted hash from the signature.

Sample Scenario: Alice Sends a Signed Document to Bob

Let's illustrate this with a simple scenario involving two characters, Alice and Bob:

1. Alice Prepares to Send the Document:

   • Alice writes a letter to Bob to ensure it reaches him without tampering.
   • She generates a hash of the letter and encrypts this hash with her private key, creating a digital signature.

2. Alice Sends the Document:

   • Alice sends the letter (in digital form) and its digital signature to Bob.

3. Bob Verifies the Document:

   • Upon receiving the letter, Bob uses Alice's public key (which she had shared with him earlier) to decrypt the digital signature, obtaining the hash value Alice generated.
   • Bob then creates a hash of the received letter. If this hash matches the one decrypted from Alice's digital signature, he can be confident the letter hasn't been altered and truly comes from Alice.

Benefits of Digital Signing

• Integrity: Ensures the content has not been altered in transit.
• Authentication: Verifies the sender's identity.
• Non-repudiation: The sender cannot deny the authenticity of the document they signed.

Conclusion

Digital signing with asymmetric keys plays a crucial role in secure communications, offering a robust method for ensuring digital documents' integrity, authenticity, and non-repudiation. By understanding and utilizing this process, individuals can protect their digital communications in an increasingly interconnected world.