• It is a simple one liner command to generate a public key from a private key, so lets say our private key is named ‘user@myserver.key’ and we want to generate the public key. To generate private (d,n) key using openssl you can use the following command: openssl genrsa -out private.pem 1024 To generate public (e,n) key from the private key.
• 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 $ openssl rsa -check -in domain.key. 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 order to export the public key from the freshly generated private RSA Key, the openssl rsa utility, which is used for processing RSA keys. The command to export a public key is as follows: openssl rsa -in private.pem -pubout -outform PEM -out public.pem This will result in a public key, due to the flag -pubout.
• Public Key Encryption and Digital Signatures using OpenSSL. I recently gave students a homework task to get familiar with OpenSSL as well as understand the use of public/private keys in public key cryptography (last year I gave same different tasks using certificates - see the steps. The tasks for the student (sender in the notes below) were to.
• Openssl rsa: Manage RSA private keys (includes generating a public key from it). Openssl rsautl: Encrypt and decrypt files with RSA keys. The key is just a string of random bytes. We use a base64 encoded string of 128 bytes, which is 175 characters. Since 175 characters is 1400 bits, even a small RSA key will be able to encrypt it.
• The RSA private key in PEM format (the most common format for X.509 certificates, CSRs and cryptographic keys) can be generated from the command line using the openssl genpkey utility. Cool Tip: Check whether an SSL Certificate or a CSR match a Private Key using the OpenSSL utility from the command line!

• Generate Rsa Public Private Key
• Openssl Generate Public Key
• Openssl Generate Public Private Key
• Openssl Generate Rsa Key Pair

I recently gave students a homework task to get familiar with OpenSSL as well as understand the use of public/private keys in public key cryptography (last year I gave same different tasks using certificates - see the steps. The tasks for the student (sender in the notes below) were to:

• Create a RSA public/private key pair
• View and understand the parameters in the key pair
• Sign a message using their private key
• Encrypt a message using the recipients (my) public key
• 'Send' the signature and ciphertext to the recipient (me)

You can generate a public-private keypair with the genrsa context (the last number is the keylength in bits): openssl genrsa -out keypair.pem 2048 To extract the public part, use the rsa context: openssl rsa -in keypair.pem -pubout -out publickey.crt Finally, convert the original keypair to PKCS#8 format with the pkcs8 context.

Then I decrypted the ciphertext and verified the signature. Of course I also had to create my own key pair and make the public key available to the sender.

The steps are shown below, first in a screencast where I provide some explanation of the options and steps, and second in text form (with little explanation) that you can view and copy and paste if needed. Note that although the steps used in both outputs are the same, the actual values differ (i.e. the output listed below is from a different set of keys than used in the screencast). /penn-plax-cascade-1000-user-manual.html.

Steps Performed by Sender

To generate the private (and public key):

The private key is encoded with Base64. To view the values:

To output just the public key to a file:

Check by looking at the invidual values:

Create a text file:

To sign the message you need to calculate its hash and then encrypt that hash using your private key. To create a hash of a message (without encrypting):

OpenSSL has an option to calculate the hash and then sign it:

To encrypt the message using RSA, use the recipients public key:

Note that direct RSA encryption should only be used on small files, with length less than the length of the key. If you want to encrypt large files then use symmetric key encryption. Two approaches to do this with OpenSSL: (1) generate a random key to be used with a symmetric cipher to encrypt the message and then encrypt the key with RSA; (2) use the smime operation, which combines RSA and a symmetric cipher to automate approach 1.

Steps Performed by Receiver

The public key was generated and made available to the sender:

To decrypt the received ciphertext:

To verify the signature of a message:

PDF version of this page, 7 Apr 2012

Created on Sat, 07 Apr 2012, 8:22pm

Generate Rsa Public Private Key

Last changed on Mon, 03 Nov 2014, 10:54am

Sometimes I need to encrypt some stuff but do not want to install PGP or GPG. I typically use OpenSSL for this kind of thing and have written a simple frontend script to achieve strong password based encryption using OpenSSL. Sometimes you need public / private key encryption though, below will show you how to do it using just OpenSSL.

Public/Private key encryption is a method used usually when you want to receive or send data to thirdparties. The system requires everyone to have 2 keys one that they keep secure – the private key – and one that they give to everyone – the public key. Data encrypted using the public key can only ever be unencrypted using the private key. This method of encryption that uses 2 keys is called asymmetric encryption.

So by example if Person A want to send Person B data in a secure fashion she just have to encrypt it with Person B’s public key, only Person B can then open the file using her private key. There are other advantages to this kind of encryption. If I met you in person and gave you my public key, I can send you something electronically using my private key to encrypt it, if the public key you have can decrypt that data then you can trust that it was sent by me, it’s mathematical proof of identity. This is the basis for Digital Signatures.

Using OpenSSL on the command line you’d first need to generate a public and private key, you should password protect this file using the -passout argument, there are many different forms that this argument can take so consult the OpenSSL documentation about that.

Openssl Generate Public Key

This creates a key file called private.pem that uses 1024 bits. This file actually have both the private and public keys, so you should extract the public one from this file:

You’ll now have public.pem containing just your public key, you can freely share this with 3rd parties.
You can test it all by just encrypting something yourself using your public key and then decrypting using your private key, first we need a bit of data to encrypt:

Openssl Generate Public Private Key

You now have some data in file.txt, lets encrypt it using OpenSSL and the public key:

This creates an encrypted version of file.txt calling it file.ssl, if you look at this file it’s just binary junk, nothing very useful to anyone. Now you can unencrypt it using the private key:

Openssl Generate Rsa Key Pair

You will now have an unencrypted file in decrypted.txt: befunky photo editor for pc free download

All of these examples use the RSA encryption method, some hard core mathematical information about it here.

There are a fair few limitations to this approach – it will only encrypt data up to the key size for example. And you really should never encrypt english plain text using a method like this. You’d use this to safely encrypt a random generated password and then aes encrypt the actual text you care about. Look in the comments for examples of that.