# OpenSSL 🔐

## Install

Install the OpenSSL on Debian based systems

```sh
sudo apt-get install openssl
```

## Commands
### Creation
Create a private key

```sh
openssl genrsa -out server.key 4096
```

Generate a new private key and certificate signing request

```sh
openssl req -out server.csr -new -newkey rsa:4096 -nodes -keyout server.key
```

Generate a self-signed certificate

```sh
openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:4096 -keyout server.key -out server.crt
```

Generate a certificate signing request (CSR) for an existing private key

```sh
openssl req -out server.csr -key server.key -new
```

Generate a certificate signing request based on an existing certificate

```sh
openssl x509 -x509toreq -in server.crt -out server.csr -signkey server.key
```

Generate a Diffie Hellman key

```sh
openssl dhparam -out dhparam.pem 2048
```

Generate a v3 certificate by signing CSR
```sh
openssl x509 -days 365 -in myCSR.csr -extfile v3.ext -CA myCA.crt -CAkey myCA.key -CAcreateserial -out userCertificate.crt
```
See below for an example `v3.ext` file
```text
authorityKeyIdentifier=keyid,issuer
basicConstraints=CA:FALSE
keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
```

### Checking
Check a certificate signing request (CSR)

```sh
openssl req -text -noout -verify -in server.csr
```

Check a private key

```sh
openssl rsa -in server.key -check
```

Check a public key

```sh
openssl rsa -inform PEM -pubin -in pub.key -text -noout
openssl pkey -inform PEM -pubin -in pub.key -text -noout
```

Check a certificate

```sh
openssl x509 -in server.crt -text -noout
openssl x509 -in server.cer -text -noout
```

Check a PKCS#12 file (.pfx or .p12)

```sh
openssl pkcs12 -info -in server.p12
```

Verify a private key matches an certificate

```sh
openssl x509 -noout -modulus -in server.crt | openssl md5
openssl rsa -noout -modulus -in server.key | openssl md5
openssl req -noout -modulus -in server.csr | openssl md5
```

Display all certificates including intermediates

```sh
openssl s_client -connect www.paypal.com:443
```

### Converting
Convert a DER file (.crt .cer .der) to PEM

```sh
openssl x509 -inform der -in server.cer -out server.pem
```

Convert a PEM file to DER

```sh
openssl x509 -outform der -in server.pem -out server.der
```

Convert a PKCS#12 file (.pfx .p12) containing a private key and certificates to PEM

```sh
openssl pkcs12 -in server.pfx -out server.pem -nodes
```

Convert a PEM certificate file and a private key to PKCS#12 (.pfx .p12)

```sh
openssl pkcs12 -export -out server.pfx -inkey server.key -in server.crt -certfile CACert.crt
```

### Other commands
Remove a passphrase from a private key

```sh
openssl rsa -in server.pem -out newserver.pem
```

Parse a list of revoked serial numbers

```sh
openssl crl -inform DER -text -noout -in list.crl
```
Encrypt files with rsautl

```sh
openssl rsautl -encrypt -in plaintext.txt -out encrypted.txt -pubin -inkey pubkey.pem
```

Decrypt files with rsautl

```sh
openssl rsautl -decrypt -in encrypted.txt -out plaintext.txt -inkey privkey.pem
```

### Exporting

Extracting Public Key from Private Key
```
openssl rsa -in privkey.pem -pubout > key.pub
```

Extracting Public Key from Certificate
```
openssl x509 -pubkey -noout -in cert.pem  > pubkey.pem

```