OpenSSL is a powerful cryptography toolkit that can be used for encryption of files and messages.
If you want to use the same password for both encryption of plaintext and decryption of ciphertext, then you have to use a method that is known as symmetric-key algorithm.
From this article you’ll learn how to encrypt and decrypt files and messages with a password from the Linux command line, using OpenSSL.
If your private key is compromised, it's game over. But I think you are asking what happens if a file containing an encrypted copy of your private key is compromised. In that case, the password must be cracked for the user to recover the private key. That is why a strong password and a slow key stretching operation are helpful. I’m getting it on my blog, as a reference to myself, so I can make a key pair quickly in the future. Make a new ssl private key:. Generate a new unencrypted rsa private key in PEM format: openssl genrsa -out privkey.pem 2048. You can create an encrypted key by adding the.
HowTo: Encrypt a File
Options | Description |
---|---|
openssl | OpenSSL command line tool |
enc | Encoding with Ciphers |
-aes-256-cbc | The encryption cipher to be used |
-salt | Adds strength to the encryption |
-in | Specifies the input file |
-out | Specifies the output file. |
Interesting fact: 256bit AES is what the United States government uses to encrypt information at the Top Secret level.
Warning: The
-salt
option should ALWAYS be used if the key is being derived from a password.Without the
The reason for this is that without the salt the same password always generates the same encryption key.-salt
option it is possible to perform efficient dictionary attacks on the password and to attack stream cipher encrypted data.When the salt is being used the first eight bytes of the encrypted data are reserved for the salt: it is generated at random when encrypting a file and read from the encrypted file when it is decrypted.
HowTo: Decrypt a File
Options | Description |
---|---|
-d | Decrypts data |
-in | Specifies the data to decrypt |
-out | Specifies the file to put the decrypted data in |
Base64 Encode & Decode
Base64 encoding is a standard method for converting 8-bit binary information into a limited subset of ASCII characters.It is needed for safe transport through e-mail systems, and other systems that are not 8-bit safe.
By default the encrypted file is in a binary format.
If you are going to send it by email, IRC, etc. you have to save encrypted file in Base64-encode.
Cool Tip: Want to keep safe your private data? Create a password protected ZIP file from the Linux command line. Really easy! Read more →
To encrypt file in Base64-encode, you should add
-a
option:Option | Description |
---|---|
-a | Tells OpenSSL that the encrypted data is in Base64-ensode |
Option
-a
should also be added while decryption:Non Interactive Encrypt & Decrypt
Warning: Since the password is visible, this form should only be used where security is not important.
By default a user is prompted to enter the password.
If you are creating a BASH script, you may want to set the password in non interactive way, using
-k
option.Cool Tip: Need to improve security of the Linux system? Encrypt DNS traffic and get the protection from DNS spoofing! Read more →
Public key cryptography was invented just for such cases.
Encrypt a file using a supplied password:
Decrypt a file using a supplied password:
While Encrypting a File with a Password from the Command Line using OpenSSLis very useful in its own right, the real power 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.pem
to verify that it starts with a-----BEGIN RSA PRIVATE KEY-----
less public.pem
to 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.
![Openssl Generate Private Key Without Password Openssl Generate Private Key Without Password](/uploads/1/2/5/7/125716790/640002304.jpg)
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.
Openssl Generate Private Key No Password
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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