Learn about some of our favorite open source intrusion detection tools as well as tips on how to use them in our Beginner's Guide to Open Source Intrusion Detection Tools paper. Download it now. Kim Crawley spent years working in general tier two consumer tech support, most of which as a representative of Windstream, a secondary American ISP. Malware related tickets intrigued her, and her knowledge grew from fixing malware problems on thousands of client PCs.
Her curiosity led her to research malware as a hobby, which grew into an interest in all things information security related.
This October, she gave her first talk at an infosec convention, a penetration testing presentation at BSides Toronto. She considers her sociological and psychological perspective on infosec to be her trademark. Given the rapid growth of social engineering vulnerabilities, always considering the human element is vital.
Benchmark your cybersecurity maturity. We use cookies to provide you with a great user experience. The need for a more secure network communication method inspired the creation of the SSH protocol. In this tutorial, we will talk about what SSH is, why it is used, and how it works. Note: The tutorial will talk about SSH2, the current version of the protocol.
The original SSH is now considered outdated and less secure. SSH short for Secure Shell is a network protocol that provides a secure way for two computers to connect remotely. SSH employs encryption to ensure that hackers cannot interpret the traffic between two connected devices.
SSH provides a layer of security for information transfer between machines. Some important use cases for SSH are:. SSH is a client-server based protocol. This means the protocol allows a device requesting information or services the client to connect to another device the server. When a client connects to a server over SSH, the machine can be controlled like a local computer.
The server has a designated TCP port over which it monitors the network, waiting for clients to initialize the connection. Before a client connects and starts issuing SSH commands , it needs to pass the authentication process. Note: Read our guide on how to use SSH to connect to a remote server for a comprehensive list of steps. Upon receiving a connection request, the server sends the client a set of supported encryption protocols.
The server uses the public key as the authentication method. This exchange results in the server and client both arriving at the same key independently by sharing certain pieces of public data and manipulating them with certain secret data.
This process is explained in greater detail later on. The symmetrical encryption key created by this procedure is session-based and constitutes the actual encryption for the data sent between server and client. Once this is established, the rest of the data must be encrypted with this shared secret. This is done prior to authenticating a client.
The server and client can both decide on a list of their supported ciphers, ordered by preference. On Ubuntu This means that if two Ubuntu Asymmetrical encryption is different from symmetrical encryption in that to send data in a single direction, two associated keys are needed.
One of these keys is known as the private key , while the other is called the public key. The public key can be freely shared with any party. It is associated with its paired key, but the private key cannot be derived from the public key. The mathematical relationship between the public key and the private key allows the public key to encrypt messages that can only be decrypted by the private key. This is a one-way ability, meaning that the public key has no ability to decrypt the messages it writes, nor can it decrypt anything the private key may send it.
The private key should be kept entirely secret and should never be shared with another party. This is a key requirement for the public key paradigm to work. The private key is the only component capable of decrypting messages that were encrypted using the associated public key.
By virtue of this fact, any entity capable decrypting these messages has demonstrated that they are in control of the private key. SSH utilizes asymmetric encryption in a few different places. During the initial key exchange process used to set up the symmetrical encryption used to encrypt the session , asymmetrical encryption is used.
In this stage, both parties produce temporary key pairs and exchange the public key in order to produce the shared secret that will be used for symmetrical encryption. SSH key pairs can be used to authenticate a client to a server. The client creates a key pair and then uploads the public key to any remote server it wishes to access.
After the symmetrical encryption is established to secure communications between the server and client, the client must authenticate to be allowed access. The server can use the public key in this file to encrypt a challenge message to the client. If the client can prove that it was able to decrypt this message, it has demonstrated that it owns the associated private key. The server then can set up the environment for the client.
Another form of data manipulation that SSH takes advantage of is cryptographic hashing. Their main distinguishing attributes are that they are never meant to be reversed, they are virtually impossible to influence predictably, and they are practically unique.
Using the same hashing function and message should produce the same hash; modifying any portion of the data should produce an entirely different hash. A user should not be able to produce the original message from a given hash, but they should be able to tell if a given message produced a given hash.
Given these properties, hashes are mainly used for data integrity purposes and to verify the authenticity of communication. These are used to ensure that the received message text is intact and unmodified. It provides several alternative options for strong authentication, and it protects the communications security and integrity with strong encryption. It is a secure alternative to the non-protected login protocols such as telnet , rlogin and insecure file transfer methods such as FTP.
The protocol works in the client-server model, which means that the connection is established by the SSH client connecting to the SSH server.
The SSH client drives the connection setup process and uses public key cryptography to verify the identity of the SSH server. After the setup phase the SSH protocol uses strong symmetric encryption and hashing algorithms to ensure the privacy and integrity of the data that is exchanged between the client and server.
There are several options that can be used for user authentication. The most common ones are passwords and public key authentication.
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