# Openssl Rsa

- Newer versions of OpenSSL say BEGIN PRIVATE KEY because they contain the private key + an OID that identifies the key type (this is known as PKCS8 format). To get the old style key (known as either PKCS1 or traditional OpenSSL format) you can do this: openssl rsa -in server.key -out servernew.key.
- Creates a new RSA key with only public components. N is the modulus common to both public and private key. E is the public exponent. This corresponds to RSAnew and uses RSAset0key. Pub fn publickeyfrompem (pem: & u8) - Result, ErrorStack src −.

OpenSSL is a giant command-line binary capable of a lot of various securityrelated utilities. Each utility is easily broken down via the first argument of`openssl`

. For instance, to generate an RSA key, the command to use will be`openssl genpkey`

.

RSA is popular format use to create asymmetric key pairs those named public and private key. We can use rsa verb to read RSA private key with the following command. $ openssl rsa -in myprivate.pem -check Read RSA Private Key.

## Generate 2048-bit AES-256 Encrypted RSA Private Key .pem

The following command will result in an output file of private.pem in whichwill be a private RSA key in the PEM format.

Let’s break this command down:

`openssl`

: The binary that contains the code to generate an RSA key (and manyother utilities).`genpkey`

: Specifies the utility to use.`-algorithm RSA`

: Specifies to use the RSA algorithm.`-aes256`

: Specifies to use the AES-256 cipher, which is newer and moresecure than DES. Default is no cipher.`-out private.pem`

: Specifies that a file named “private.pem” should becreated with the contents of the private key. Default is`STDOUT`

.

When executing this command, it will ask for a password to encrypt the keywith. After selecting a password, a file will be created in the currentdirector named `private.pem`

.

Private RSA keys generated with this utility start with the text `-----BEGIN PRIVATE KEY-----`

.

You can inspect this file with the command `cat private.pem`

.

## Export Public RSA Key From Private Key

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.

### Openssl Rsa -in

The command to export a public key is as follows:

This will result in a public key, due to the flag **-pubout**.

Inspect this file with `cat public.pem`

:

The public key can be uploaded to other servers and services to encrypt datafor the private key to decrypt.

This file will start with `-----BEGIN PUBLIC KEY-----`

. If this file doesn’tstart with “BEGIN PUBLIC KEY”, do not upload it as a public key to any source!

### Openssl Rsa Sign

I am trying to implement a signing function in C++ using RSA.

Here's how I wanted to do this:

- First I calculate the SHA1 hash (not using openssl but another implementation).

- But then what? Should I use RSA_private_encrypt or rsa_sign? When I use RSA_private_encrypt the result is different from when I use rsa_sign... The openssl support pages mention that in case of RSA_PKCS1_PADDING (that's the one I use) I should use rsa_sign. Is there any way around this?

I thought that signing was a two step process: hash + RSA encryption of hash. Am I doing something wrong?

Thanks.

Regards,

Bob D.

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