Key generation is the process of generating keys in cryptography. A key is used to encrypt and decrypt whatever data is being encrypted/decrypted.
A device or program used to generate keys is called a key generator or keygen.
In public key cryptography, each person has a set of keys.To send a message securely to a particular person, you encrypt your message using their public key.An attacker may be able to trick you into using their key, which means that they will be able to read your message, instead of the intended recipient.
Generation in cryptography[edit]
Modern cryptographic systems include symmetric-key algorithms (such as DES and AES) and public-key algorithms (such as RSA). Symmetric-key algorithms use a single shared key; keeping data secret requires keeping this key secret. Public-key algorithms use a public key and a private key. The public key is made available to anyone (often by means of a digital certificate). A sender encrypts data with the receiver's public key; only the holder of the private key can decrypt this data.
Since public-key algorithms tend to be much slower than symmetric-key algorithms, modern systems such as TLS and SSH use a combination of the two: one party receives the other's public key, and encrypts a small piece of data (either a symmetric key or some data used to generate it). The remainder of the conversation uses a (typically faster) symmetric-key algorithm for encryption.
Computer cryptography uses integers for keys. In some cases keys are randomly generated using a random number generator (RNG) or pseudorandom number generator (PRNG). A PRNG is a computeralgorithm that produces data that appears random under analysis. PRNGs that use system entropy to seed data generally produce better results, since this makes the initial conditions of the PRNG much more difficult for an attacker to guess. Another way to generate randomness is to utilize information outside the system. veracrypt (a disk encryption software) utilizes user mouse movements to generate unique seeds, in which users are encouraged to move their mouse sporadically. In other situations, the key is derived deterministically using a passphrase and a key derivation function.
Many modern protocols are designed to have forward secrecy, which requires generating a fresh new shared key for each session.
Classic cryptosystems invariably generate two identical keys at one end of the communication link and somehow transport one of the keys to the other end of the link.However, it simplifies key management to use Diffie–Hellman key exchange instead.
The simplest method to read encrypted data without actually decrypting it is a brute-force attack—simply attempting every number, up to the maximum length of the key. Therefore, it is important to use a sufficiently long key length; longer keys take exponentially longer to attack, rendering a brute-force attack impractical. Currently, key lengths of 128 bits (for symmetric key algorithms) and 2048 bits (for public-key algorithms) are common.
Generation in physical layer[edit]Wireless channels[edit]
A wireless channel is characterized by its two end users. By transmitting pilot signals, these two users can estimate the channel between them and use the channel information to generate a key which is secret only to them.[1] The common secret key for a group of users can be generated based on the channel of each pair of users.[2]
Optical fiber[edit]
A key can also be generated by exploiting the phase fluctuation in a fiber link.[clarification needed]
See also[edit]
References[edit]
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Password authentication is the default method most SSH (Secure Shell) clients use to authenticate with remote servers, but it suffers from potential security vulnerabilities, like brute-force login attempts. An alternative to password authentication is public key authentication, in which you generate and store on your computer a pair of cryptographic keys and then configure your server to recognize and accept your keys. Using key-based authentication offers a range of benefits:
This guide will explain how the SSH key login scheme works, how to generate an SSH key, and how to use those keys with your Linode.
Note
If you’re unfamiliar with SSH connections, review the Getting Started with Linode guide.
How SSH Keys Work
SSH keys are generated in pairs and stored in plain-text files. The key pair (or keypair) consists of two parts:
When a site or service asks for your SSH key, they are referring to your SSH public key (
id_rsa.pub ). For instance, services like GitHub and Gitlab allow you to place your SSH public key on their servers to streamline the process of pushing code changes to remote repositories.
The authorized_keys File
In order for your Linode to recognize and accept your key pair, you will need to upload your public key to your server. More specifically, you will need to upload your public key to the home directory of the user you would like to log in as. If you would like to log in to more than one user on the server using your key pair, you will need to add your public key to each of those users.
To set up SSH key authentication for one of your server’s users, add your public key to a new line inside the user’s
authorized_keys file. This file is stored inside a directory named .ssh/ under the user’s home folder. A user’s authorized_keys file can store more than one public key, and each public key is listed on its own line. If your file contains more than one public key, then the owner of each key listed will be able to log in as that user.
Granting Someone Else Access to your Server
To give someone else access to your server’s user, simply add their public key on a new line in your
authorized_keys file, just as you would add your own. To revoke access for that person, remove that same line and save the changes.
Challenge-Response
When logging in to a server using SSH, if there is a public key on file on that server, the server will create a challenge. This challenge will be crafted in such a way that only the holder of the private SSH key will be able to decipher it.
This challenge-response action happens without any user interaction. If the person attempting to log in has the corresponding private key, then they will be safely logged in. If not, the login will either fail or fall back to a password-based authentication scheme.
SSH Key Passphrases
You can optionally provide an additional level of security for your SSH keys by encrypting them with a passphrase at the time of creation. When you attempt to log in using an encrypted SSH key, you will be prompted to enter its passphrase. This is not to be confused with a password, as this passphrase only decrypts the key file locally and is not transferred over the Internet as a password might be.
If you’d like to set up your logins so that they require no user input, then creating a passphrase might not be desirable, but it is strongly recommended nevertheless.
Linux and macOSGenerate a Key Pair
Perform the steps in this section on your local machine.
Upload your Public Key
There are a few different ways to upload your public key to your Linode from Linux and macOS client systems:
Using ssh-copy-idssh-copy-id is a utility available on some operating systems that can copy a SSH public key to a remote server over SSH.
Using Secure Copy (scp)
Secure Copy (
scp ) is a tool that copies files from a local computer to a remote server over SSH:
Force System To Use Self Generated Public Key WestCaution
These instructions will overwrite any existing contents of the
authorized_keys file on your server. If you have already set up other public keys on your server, use the ssh-copy-id command or enter your key manually.
Force System To Use Self Generated Public KeychainManually Copy an SSH Key
You can also manually add an SSH key to a server:
Connect to the Remote Server
Windows
The following instructions use the PuTTY software to connect over SSH, but other options are available on Windows too.
Generate a Key Pair with PuTTY
Manually Copy the SSH Key with PuTTY
Using WinSCP
Uploading a public key from Windows can also be done using WinSCP:
Caution
Force System To Use Self Generated Public Key Search
These instructions will overwrite any existing contents of the
authorized_keys file on your server. If you have already set up other public keys on your server, use the PuTTY instructions instead.
Connect to the Remote Server with PuTTY
Start PuTTY and Load your saved session. You’ll be prompted to enter your server user’s login name as before. However, this time you will be prompted for your private SSH key’s passphrase rather than the password for your server’s user. Enter the passphrase and press Enter.
Force System To Use Self Generated Public Key LargoTroubleshooting
If your SSH connections are not working as expected, or if you have locked yourself out of your system, review the Troubleshooting SSH guide for troubleshooting help.
Upload your SSH Key to the Cloud Manager
It is possible to provision each new Linode you create with an SSH public key automatically through the Cloud Manager.
Next Steps
After you set up your SSH keys and confirm they are working as expected, review the How to Secure Your Server guide for instructions on disabling password authentication for your server.
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