While Encrypting a File with a Password from the Command Line using OpenSSL is very useful in its own right, the real power of the OpenSSL library is its ability to support the use of public key cryptograph for encrypting or validating data in an unattended manner (where the password is not required to encrypt) is done with public keys. The Commands to Run. Generate an RSA private key using default parameters: openssl genpkey -algorithm RSA -out key.pem. Encrypt output private key using 128 bit AES and the passphrase 'hello': openssl genpkey -algorithm RSA -out key.pem -aes-128-cbc -pass pass:hello. Generate a 2048 bit RSA key using 3 as the public exponent.
genpkey - generate a private key
opensslgenpkey[-out filename][-outform PEM DER][-pass arg][-cipher][-engine id][-paramfile file][-algorithm alg][-pkeyopt opt:value][-genparam][-text]
The genpkey command generates a private key.
the output filename. If this argument is not specified then standard output isused.
This specifies the output format DER or PEM.
the output file password source. For more information about the format of argsee the PASS PHRASE ARGUMENTS section in openssl.
This option encrypts the private key with the supplied cipher. Any algorithmname accepted by EVP_get_cipherbyname() is acceptable such as des3.
specifying an engine (by its unique id string) will cause genpkeyto attempt to obtain a functional reference to the specified engine,thus initialising it if needed. The engine will then be set as the defaultfor all available algorithms. If used this option should precede all otheroptions.
public key algorithm to use such as RSA, DSA or DH. If used this option mustprecede any -pkeyopt options. The options -paramfile and -algorithmare mutually exclusive.
set the public key algorithm option opt to value. The precise set ofoptions supported depends on the public key algorithm used and itsimplementation. See KEY GENERATION OPTIONS below for more details.
generate a set of parameters instead of a private key. If used this option mustprecede and -algorithm, -paramfile or -pkeyopt options.
Some public key algorithms generate a private key based on a set of parameters.They can be supplied using this option. If this option is used the public keyalgorithm used is determined by the parameters. If used this option mustprecede and -pkeyopt options. The options -paramfile and -algorithmare mutually exclusive.
Print an (unencrypted) text representation of private and public keys andparameters along with the PEM or DER structure.
The options supported by each algorith and indeed each implementation of analgorithm can vary. The options for the OpenSSL implementations are detailedbelow.
The number of bits in the generated key. If not specified 1024 is used.
The RSA public exponent value. This can be a large decimal orhexadecimal value if preceded by 0x. Default value is 65537.
The number of bits in the generated parameters. If not specified 1024 is used.
The number of bits in the prime parameter p.
The value to use for the generator g.
If this option is set then the appropriate RFC5114 parameters are usedinstead of generating new parameters. The value num can take thevalues 1, 2 or 3 corresponding to RFC5114 DH parameters consisting of1024 bit group with 160 bit subgroup, 2048 bit group with 224 bit subgroupand 2048 bit group with 256 bit subgroup as mentioned in RFC5114 sections2.1, 2.2 and 2.3 respectively.
the EC curve to use.
Gost 2001 support is not enabled by default. To enable this algorithm,one should load the ccgost engine in the OpenSSL configuration file.See README.gost file in the engines/ccgost directiry of the sourcedistribution for more details.
Use of a parameter file for the GOST R 34.10 algorithm is optional.Parameters can be specified during key generation directly as well asduring generation of parameter file.
Specifies GOST R 34.10-2001 parameter set according to RFC 4357.Parameter set can be specified using abbreviated name, object short name ornumeric OID. Following parameter sets are supported:
The use of the genpkey program is encouraged over the algorithm specificutilities because additional algorithm options and ENGINE provided algorithmscan be used.
Generate an RSA private key using default parameters:
Encrypt output private key using 128 bit AES and the passphrase 'hello':
Generate a 2048 bit RSA key using 3 as the public exponent:
Generate 1024 bit DSA parameters:
Generate DSA key from parameters:
Generate 1024 bit DH parameters:
Output RFC5114 2048 bit DH parameters with 224 bit subgroup:
Generate DH key from parameters:
Skip to main contentPublished: 25-10-2018 Author: Remy van Elst Text only version of this article
This small tutorial will show you how to use the openssl command line to encryptand decrypt a file using a public key. We will first generate a random key,encrypt that random key against the public key of the other person and use thatrandom key to encrypt the actual file with using symmetric encryption.
Because of how the RSA algorithm works it is not possible to encrypt largefiles. If you create a key of n bits, then the file you want to encrypt mustnot larger than (n minus 11) bits. The most effective use of RSA crypto is toencrypt a random generated password, then encrypt the file with the passwordusing symmetric crypto. If the file is larger then the key size the encryptioncommand will fail:
We generate a random file and use that as the key to encrypt the large file withsymmetric crypto. That random file acts as the password so to say. We encryptthe large file with the small password file as password. Then we send theencrypted file and the encrypted key to the other party and then can decrypt thekey with their public key, the use that key to decrypt the large file.
The following commands are relevant when you work with RSA keys:
openssl genrsa: Generates an RSA private keys.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 128bytes, which is 175 characters. Since 175 characters is 1400 bits, even a smallRSA key will be able to encrypt it.
Let the other party send you a certificate or their public key. If they send toa certificate you can extract the public key using this command:
Use the following command to generate the random key:
Do this every time you encrypt a file. Use a new key every time!
Update 25-10-2018
The key format is HEX because the base64 format adds newlines. The -passargument later on only takes the first line of the file, so the full key is notused. (Thanks Ken Larson for pointing this to me)
Use the following command to encrypt the large file with the random key:
The file size doesn't grows that much:
It's encrypted however:
Use the following command to encrypt the random keyfile with the other personspublic key:
You can safely send the key.bin.enc and the largefile.pdf.enc to the otherparty.
You might want to sign the two files with your public key as well.
Mar 31, 2018 Generate public key and store into a file. 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 and name it ‘authorizedkeys’. Openssl generate private key ssh. Add your SSH private key to the ssh-agent. If you created your key with a different name, or if you are adding an existing key that has a different name, replace idrsa in the command with the name of your private key file. $ ssh-add /.ssh/idrsa; Add the SSH key to your GitHub account. While Encrypting a File with a Password from the Command Line using OpenSSL is very useful in its own right, the real power of the OpenSSL library is its ability to support the use of public key cryptograph for encrypting or validating data in an unattended manner (where the password is not required to encrypt) is done with public keys. The Commands to Run.
If you want to decrypt a file encrypted with this setup, use the followingcommand with your privte key (beloning to the pubkey the random key was cryptedto) to decrypt the random key:
This will result in the decrypted random key we encrypted the file in.
Once you have the random key, you can decrypt the encrypted file with thedecrypted key:
This will result in the decrypted large file.
Tags: ca, certificate, decrypt, encrypt, openssl, pki, ssl, tls, tutorials