Acce55ing Rem0te Systems & File P3rms
What is SSH?
SSH or Secure SHell is network protocol for secure/encrypted communications between systems
SSH is often used for remote administration of "headless" servers in a client/server model.
Understanding SSH involves understanding of many key security concepts such as: encryption, ports, sockets, shells, services, connectivity.
How does it work?
SSH is based on the concept public key cryptography where a user must own a generated public/private key pair, and requires completion of a 3 way handshake to create a secure connection between systems.
Messages are created with a private key and can only be decrypted on the receiving end if that user has the associated public key.
Likewise returned messages are created using the public key and only a user owning the private key can successfully decrypt the message.
How does it work(more)?
SSH requires a few key components to access a remote system.
- Generation of a public/private key pair
ssh-keygen -t rsa -b 4096 -C "some.user@somedomain.com"2. Addition of public key to a remote systems ~/.ssh/authorized_keys file
3. Configuration of SSH service on remote systems /etc/ssh/sshd_config file
more ssh | grep skillz
$ ssh --helpMac/Linux Users:
# Default Connection Linux/Mac
$ ssh user@somedomain.com
# Custom Port Connection Linux/Mac
$ ssh -p 2222 someuser@192.168.1.19
# Command line Putty Usage | PATH must be set
C:\Users\MyUser putty.exe -ssh someuser@192.168.1.19
To make a connection:
Windows Users:
https://putty.org/
File Permissions (Linux)
Files and Directories, in both Windows and Linux, have similar concepts of ownership
It usually comes down to who can:
- Read
- Write
- Execute
In Linux these permissions are based on binary calculations
- Read - 4
- Write - 2
- Execute - 1
more File Permissions
To view file or directory permissions:
$ ls -la some/file/path
So who owns things?
Ownership generally comes down to 2 main categories:
- Users
- Groups(many users)
Group permissions are much easier to manage at scale than individual users, so it's best to categorize/segment your users
How to find files by properties?
Sometimes you need to search a system to find out ownership by user, group, or permissions:
The find utility allows us to search a file system for files matching certain characteristics.
# Find all files owned by user jason
find / -user jason
# Find all files owned by the group admins
find / -group admins
# Find a file by name
find / -name somefile.txt
# You can mix commands as well
find / -user jason -group admins
# There are many other options including:
- File Permissions
- Size of file
- Case insensitive file match
- File Path
- ...and morepractice!
Accessing Remote Systems & File Perms
By Jason Sewell
