# OpenSSL
### Basic Usage
**Generating cryptographic keys:**
OpenSSL can generate different types of cryptographic keys, such as RSA, DSA, and ECDSA. The `genrsa` command is used to generate an RSA private key. For example:
```
openssl genrsa -out private.key 2048
```
**Creating a digital certificate:**
OpenSSL can be used to generate self-signed certificates or certificate signing requests (CSRs). The `req` command is used for this purpose. For example, to generate a self-signed certificate:
```
openssl req -new -key private.key -out certificate.crt
```
**Encrypting and decrypting files:**
OpenSSL provides symmetric and asymmetric encryption capabilities. The `enc` command is used for file encryption and decryption. For example, to encrypt a file using AES-256:
```
openssl enc -aes-256-cbc -salt -in plaintext.txt -out encrypted.bin
```
**Generating a hash of a file:**
OpenSSL can generate message digests or hash values of files using various algorithms such as MD5, SHA-1, and SHA-256. The `dgst` command is used for this purpose. For example:
```
openssl dgst -sha256 file.txt
```
**Creating and verifying digital signatures:**
OpenSSL can create digital signatures using private keys and verify them using corresponding public keys. The `dgst` and `rsautl` commands are used for this purpose. For example, to sign a file using an RSA private key:
```csharp
openssl dgst -sha256 -sign private.key -out signature.bin file.txt
```
To verify the signature:
```vbnet
openssl dgst -sha256 -verify public.key -signature signature.bin file.txt
```
**Establishing secure connections (TLS/SSL):**
OpenSSL provides utilities for testing and establishing secure connections over networks. The `s_client` command is used to connect to an SSL/TLS server. For example:
```arduino
openssl s_client -connect example.com:443
```
## How to extract files using OpenSSL
Set a Listener
Send the file with openssl
We cant extract the file via netcat
`Well, we can extract but we can't read it`
Generate a private key
Open a listener with the private key
Now we can send the file
#### As we can see in the example above, not only the "server" must contain the certificates but also the "client". In order to receive the file correctly.
