View Dh Key Generated From Openssl Test Session
An example of using OpenSSL operations to perform a Diffie-Hellmen secret key exchange (DHKE). The goal in DHKE is for two users to obtain a shared secret key, without any other users knowing that key. The exchange is performed over a public network, i.e. all messages sent between the two users can be intercepted and read by any other user. The protocol makes use of modular arithmetic and especially exponentials. The security of the protocol relies on the fact that solving a discrete logarithm (the inverse of an exponential) is practically impossible when large enough values are used.
The.key file corresponds to the private key itself. If you open your.key file in a text editor you would see that they have -BEGIN RSA PRIVATE KEY- as the prefix and -END RSA PRIVATE KEY. DH: OpenSSL commandline has three options for creating certs, but all of them either selfsign the cert or require a selfsigned CSR, and DH can't do either of those. OpenSSL library called from a program you write can construct an X509 object (cert) containing a DH publickey, subject and other attributes as you specify, signed by an RSA key corresponding to a parent (CA) cert. Look at the code. The following is a sample interactive session in which the user invokes the prime command twice before using the quit command to terminate the session. OpenSSL prime -generate -bits 9 OpenSSL prime -generate -bits 9 OpenSSL quit Basic Tasks. This section is a brief tutorial on performing the most basic tasks using OpenSSL.
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Wikipedia has a description and example of DHKE. My lecture slides on public key cryptography also include a description. My description of DHKE starts at about 39m 30s into the screencast available on YouTube. It includes a simple example starting at 47m 53s. View below to go straight to the DHKE portion of the lecture.
OpenSSL provides both a library of security operations you can access from your own software, as well as a command line mode. In the past I've given examples of using OpenSSL to generate RSA keys as well as encrypt and sign with RSA. In the following I demonstrate using OpenSSL for DHKE.
DHKE is performed by two users, on two different computers. For my demo I do everything on one computer. The steps performed by each user are the same, but just with different files. In the following there is user 1 and user 2.
Steps for Diffie-Hellman Key Exchange with OpenSSL
Generate the Diffie-Hellman global public parameters, saving them in the file dhp.pem:
Display the generated global public parameters, first in the encoded form, then in the text form:
Each user now uses the public parameters to generate their own private and public key, saving them in the file dhkey1.pem (for user 1) and dhkey2.pem (for user 2):
The other user uses the same public parameters, dhp.pem, to generate their private/public key:
The users must exchange their public keys. First extract the public key into the file dhpub1.pem (and similar user 2 creates dh2pub.pem - this step is not shown below):
After exchanging public keys, i.e. the files dhpub1.pem and dhpub2.pem, each user can derive the shared secret. User 1 performs the following to output the secret, a 128 Byte binary value into the file secret1.bin:
The other user does the same using their private key and user 1's public key to produce secret2.bin:
The secrets should be the same:
PDF version of this page, 27 Jan 2013
Created on Sun, 27 Jan 2013, 1:24pm
Last changed on Mon, 03 Nov 2014, 10:46am
While Encrypting a File with a Password from the Command Line using OpenSSLis very useful in its own right, the real powerAdobe photoshop cs5 product key generator. of the OpenSSL library is itsability to support the use of public key cryptograph for encrypting orvalidating data in an unattended manner (where the password is not required toencrypt) is done with public keys.
The Commands to Run
Generate a 2048 bit RSA Key
You can generate a public and private RSA key pair like this:
openssl genrsa -des3 -out private.pem 2048
That generates a 2048-bit RSA key pair, encrypts them with a password you provideand writes them to a file. You need to next extract the public key file. You willuse this, for instance, on your web server to encrypt content so that it canonly be read with the private key.
Export the RSA Public Key to a File
This is a command that is
openssl rsa -in private.pem -outform PEM -pubout -out public.pem
The -pubout flag is really important. Be sure to include it.
Next open the public.pem and ensure that it starts with-----BEGIN PUBLIC KEY-----. This is how you know that this file is thepublic 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
A previous version of the post gave this example in error.
openssl rsa -in private.pem -out private_unencrypted.pem -outform PEM
The error is that the -pubout was dropped from the end of the command.That changes the meaning of the command from that of exporting the public keyto exporting the private key outside of its encrypted wrapper. Inspecting theoutput file, in this case private_unencrypted.pem clearly shows that the keyis a RSA private key as it starts with -----BEGIN RSA PRIVATE KEY-----.
Visually Inspect Your Key Files
It is important to visually inspect you private and public key files to makesure that they are what you expect. OpenSSL will clearly explain the nature ofthe key block with a -----BEGIN RSA PRIVATE KEY----- or -----BEGIN PUBLIC KEY-----.
You can use less to inspect each of your two files in turn:
less private.pemto verify that it starts with a-----BEGIN RSA PRIVATE KEY-----less public.pemto verify that it starts with a-----BEGIN PUBLIC KEY-----
The next section shows a full example of what each key file should look like.
The Generated Key Files
The generated files are base64-encoded encryption keys in plain text format.If you select a password for your private key, its file will be encrypted withyour password. Be sure to remember this password or the key pair becomes useless.
The private.pem file looks something like this:
The public key, public.pem, file looks like:
Protecting Your Keys
Depending on the nature of the information you will protect, it’s important tokeep the private key backed up and secret. The public key can be distributedanywhere or embedded in your web application scripts, such as in your PHP,Ruby, or other scripts. Again, backup your keys!
Remember, if the key goes away the data encrypted to it is gone. Keeping aprinted copy of the key material in a sealed envelope in a bank safety depositbox is a good way to protect important keys against loss due to fire or harddrive failure.
Oh, and one last thing.
If you, dear reader, were planning any funny business with the private key that I have just published here. Know that they were made especially for this series of blog posts. I do not use them for anything else.
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