Posts on Hands On Cybersecurity Learning Blog

Crypto Lab 4- Key Exchange

Thu, 05 Dec 2024 00:00:00 +0000

Diffie-Hellman key exchange is a method that allows two parties to establish a shared secret over an insecure channel. Here’s how you can perform a basic Diffie-Hellman key exchange using OpenSSL on Linux:

Step-by-Step Demo

Generate Diffie-Hellman Parameters:

openssl dhparam -out dhparam.pem 2048

Generate Private Keys for Both Parties:

For Party A:

openssl genpkey -paramfile dhparam.pem -out privateA.pem

For Party B:

openssl genpkey -paramfile dhparam.pem -out privateB.pem

Extract Public Keys from the Private Keys:

For Party A:

openssl pkey -in privateA.pem -pubout -out publicA.pem

For Party B:

  openssl pkey -in privateB.pem -pubout -out publicB.pem

Generate the Shared Secret:
- For Party A (using Party B’s public key):

openssl pkeyutl -derive -inkey privateA.pem -peerkey publicB.pem -out shared_secret_A.bin

For Party B (using Party A’s public key):

     openssl pkeyutl -derive -inkey privateB.pem -peerkey publicA.pem -out shared_secret_B.bin

Verify the Shared Secrets Match:

   diff shared_secret_A.bin shared_secret_B.bin && echo "Shared secrets match!" || echo "Shared secrets do not match!"

Explanation

Step 1: Generates Diffie-Hellman parameters (a shared foundation) which both parties use.
Step 2: Each party generates their private keys using the shared parameters.
Step 3: Extracts public keys from the private keys to be shared with the other party.
Step 4: Each party generates a shared secret using their private key and the other party’s public key.
Step 5: Verifies that both parties have derived the same shared secret.

This demonstration helps you understand the process of establishing a shared secret securely. If you have more questions or need further details, feel free to ask!

Crypto Lab 3 - Using Digital Signatures

Wed, 04 Dec 2024 00:00:00 +0000

Digital signatures provide an electronic counterpart to physical signatures, using asymmetric cryptography to achieve the following

Authentication**: The person owning the public key used to sign the message is the one who signed it.
Integrity: The message was not altered after being signed.
Non-repudiation: The sender can prove these facts to a third party if necessary.

Behind the scenes, digital signatures depend on two things:

A collision-resistant hash function that ensures no two inputs produce the same output.
Asymmetric key pair: Anything encrypted with one key can only be decrypted with the other key from the pair.

Let’s walk through an example of using digital signatures on the Linux command line involving two users, mikey and bart, using gpg.

Crypto Lab 2 - Using Asymmetric keys

Tue, 03 Dec 2024 00:00:00 +0000

Asymmetric encryption, also known as public key cryptography, uses a pair of keys: a public key for encryption and a private key for decryption. Each user has a key pair, and anything encrypted with one key can be decrypted with the other key from the same pair.

Please refer to pre-requisite for this blog to ensure that you have two users setup on Linux.

Scenario

mikey wants to send an encrypted file to bart.
mikey uses bart’s public key to encrypt the file.
bart uses his private key to decrypt the file.
The file to be encrypted is turing_bio stored at /srv/shared

bart’s Side (Generating the keys)

bart generates a key pair (public and private keys):

Crypto Lab 1 - Using Symmetric keys

Mon, 02 Dec 2024 00:00:00 +0000

Symmetric encryption, also known as shared secret encryption, uses the same key for both encryption and decryption. If one user encrypts a message with a secret key, the recipient must use the same key to decrypt it.

Let’s walk through an example of symmetric key encryption on the Linux command line involving two users, mikey and bart, using gpg . In this case the shared key is the passphrase used to encrypt and decrypt.

Linux Basics - Adding users and groups

Sun, 01 Dec 2024 00:00:00 +0000

This short introductory post will walk you through adding a user, creating a group, adding the user to the group and sudoers, and setting up a shared folder with proper permissions on Ubuntu Linux.

The end goal is to end up with two user who can play the role of Alice and Bob as is typically the case for lot of cryptographic operations.

[! IMPORTANT] This blog assumes you already are logged into Ubuntu Linux with one user and all we are doing here is creating a second one. Alternately you can reuse the same script and create two distinct users if you wish to do so.