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To extract public key from the private key file into separate public key file you use your openssl rsa -in private.pem -pubout -out public.pem command. When you produce a public key this way, it is extracted from the private key file, not calculated.
OpenSSL
The public key is like the keyhole, as it can be installed on any door or device that the matching private key should have access to. In terms of server administration, any device that has your public key installed will be able to authenticate you using your private key when you send it. How to Generate a Public and Private Keypair. Windows Users. I want to extract the public and private key from my PKCS#12 file for later use in SSH-Public-Key-Authentication. Right now, I'm generating keys via ssh-keygen which I put into.ssh/authorizedkey, respective somewhere on the client-side. In future, I want to use the keys from a PKCS#12 container, so I've to extract the public-key first from PKCS#12 and then put them into the.ssh/authorized. Next open the public.pem and ensure that it starts with -BEGIN PUBLIC KEY-. This is how you know that this file is the public key of the pair and not a private key. To check the file from the command line you can use the less command, like this: less public.pem. Do Not Run This, it Exports the Private Key. Keys are the basis of public key algorithms and PKI.Keys usually come in pairs, with one half being the public key and the other half being the private key. With OpenSSL, the private key contains the public key information as well, so a public key doesn’t need to be generated separately. Public keys come in several flavors, using different cryptographic algorithms.
OpenSSL is a CLI (Command Line Tool) which can be used to secure the server to generate public key infrastructure (PKI) and HTTPS. This article helps you as a quick reference to understand OpenSSL commands which are very useful in common, and for everyday scenarios especially for system administrators.
Certificate Signing Requests (CSRs)
If we want to obtain SSL certificate from a certificate authority (CA), we must generate a certificate signing request (CSR). A CSR consists of mainly the public key of a key pair, and some additional information. Both these components are merged into the certificate whenever we are signing for the CSR.
While generating a CSR, the system will prompt for information regarding the certificate and this information is called as Distinguished Name (DN). The important field in the DN is the Common Name (CN) which should be the FQND (Fully Qualified Domain Name) of the server or the host where we intend to use the certificate with.
The next item in a DN is to provide the additional information about our business or organization. If we purchase an SSL certificate from a certificate authority (CA), it is very important and required that these additional fields like “Organization” should reflect your organization for details.
Here is a general example for the CSR information prompt, when we run the OpenSSL command to generate the CSR.
We can also provide the information by non-interactive answers for the CSR information generation, we can do this by adding the –subj option to any OpenSSL commands that we try to generate or run.
Below is an example for the –subj option where we can provide the information of the organization where we want to use this CSR.
Generating CSRs
In this section, we will cover about OpenSSL commands which are related to generating the CSR. This CSR can be used to request an SSL certificate from a certificate authority.
Generate a Private Key and a CSR
If we want to use HTTPS (HTTP over TLS) to secure the Apache or Nginx web servers (using a Certificate Authority (CA) to issue the SSL certificate). Also, the ‘.CSR’ which we will be generating has to be sent to a CA for requesting the certificate for obtaining CA-signed SSL.
Below is the command to create a 2048-bit private key for ‘domain.key’ and a CSR ‘domain.csr’ from the scratch.
The ‘–newkey rsa:2048’ is the option which we are specifying that the key should be 2048-bit using the RSA algorithm. The ’ –nodes’ option is to specifying that the private key should not be encrypted with a pass phrase. The ‘-new’ option, indicates that a CSR is being generated.
Generate a CSR from an Existing Private Key
Here we will learn about, how to generate a CSR for which you have the private key.
Below is the command to create a new .csr file based on the private key which we already have.
Generate a CSR from an Existing Certificate and Private key
Here we can generate or renew an existing certificate where we miss the CSR file due to some reason. Here, the CSR will extract the information using the .CRT file which we have.
Use Public Key To Generate Private Key Openssl Online
Below is the example for generating –
Where -x509toreq is specified that we are using the x509 certificate files to make a CSR.
Generating a Self-Singed Certificates
Here we will generate the Certificate to secure the web server where we use the self-signed certificate to use for development and testing purpose.
Here, we generate self-signed certificate using –x509 option, we can generate certificates with a validity of 365 days using –days 365 and a temporary .CSR files are generated using the above information.
Viewing the Certificates Files
Please note that, CSR files are encoded with .PEM format (which is not readable by the humans). This is required to view a certificate. In this section, we can cover the OpenSSL commands which are encoded with .PEM files.
![Key Key](/uploads/1/2/6/1/126173971/536836524.jpg)
Viewing CSR Files Entires
Use Public Key To Generate Private Key Openssl Access
The below command will be used to view the contents of the .CRT files Ex (domain.crt) in the plain text format.
Working with Private Keys
In this section, will see how to use OpenSSL commands that are specific to creating and verifying the private keys.
Create a Private Key
Below is the command to create a password-protected and, 2048-bit encrypted private key file (ex. domain.key) –
Enter a password when prompted to complete the process.
Verify a Private Key
Below is the command to check that a private key which we have generated (ex: domain.key) is a valid key or not
If the private key is encrypted, you will be prompted to enter the pass phrase. Upon the successful entry, the unencrypted key will be the output on the terminal.
In this article, we have learnt some commands and usage of OpenSSL commands which deals with SSL certificates where the OpenSSL has lots of features. We will learn more features and usage in the future. I hope this article will help us to understand some basic features of the OpenSSL.
< Cryptography
Download and install the OpenSSL runtimes. If you are running Windows, grab the Cygwin package.
OpenSSL can generate several kinds of public/private keypairs.RSA is the most common kind of keypair generation.[1]
Other popular ways of generating RSA public key / private key pairs include PuTTYgen and ssh-keygen.[2][3]
Generate an RSA keypair with a 2048 bit private key[edit]
Execute command: 'openssl genpkey -algorithm RSA -out private_key.pem -pkeyopt rsa_keygen_bits:2048'[4] (previously “openssl genrsa -out private_key.pem 2048”)
e.g.
Make sure to prevent other users from reading your key by executing chmod go-r private_key.pem afterward.
Extracting the public key from an RSA keypair[edit]
Execute command: 'openssl rsa -pubout -in private_key.pem -out public_key.pem'
e.g.
A new file is created, public_key.pem, with the public key.
It is relatively easy to do some cryptographic calculations to calculate the public key from the prime1 and prime2 values in the public key file.However, OpenSSL has already pre-calculated the public key and stored it in the private key file.So this command doesn't actually do any cryptographic calculation -- it merely copies the public key bytes out of the file and writes the Base64 PEM encoded version of those bytes into the output public key file.[5]
Viewing the key elements[edit]
Execute command: 'openssl rsa -text -in private_key.pem'
All parts of private_key.pem are printed to the screen. This includes the modulus (also referred to as public key and n), public exponent (also referred to as e and exponent; default value is 0x010001), private exponent, and primes used to create keys (prime1, also called p, and prime2, also called q), a few other variables used to perform RSA operations faster, and the Base64 PEM encoded version of all that data.[6](The Base64 PEM encoded version of all that data is identical to the private_key.pem file).
Password-less login[edit]
Often a person will set up an automated backup process that periodically backs up all the content on one 'working' computer onto some other 'backup' computer.
Because that person wants this process to run every night, even if no human is anywhere near either one of these computers, using a 'password-protected' private key won't work -- that person wants the backup to proceed right away, not wait until some human walks by and types in the password to unlock the private key.Many of these people generate 'a private key with no password'.[7]Some of these people, instead, generate a private key with a password,and then somehow type in that password to 'unlock' the private key every time the server reboots so that automated toolscan make use of the password-protected keys.[8][3]
Further reading[edit]
- ↑Key Generation
- ↑Michael Stahnke.'Pro OpenSSH'.p. 247.
- ↑ ab'SourceForge.net Documentation: SSH Key Overview'
- ↑'genpkey(1) - Linux man page'
- ↑'Public – Private key encryption using OpenSSL'
- ↑'OpenSSL 1024 bit RSA Private Key Breakdown'
- ↑'DreamHost: Personal Backup'.
- ↑Troy Johnson.'Using Rsync and SSH: Keys, Validating, and Automation'.
- Internet_Technologies/SSH describes how to use 'ssh-keygen' and 'ssh-copy-id' on your local machine so you can quickly and securely ssh from your local machine to a remote host.
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