# Converting PEM to crt and key
If you receive pem formatted certificate and key files from a CA registrar, you will need to convert them for use by a linux host.
## Bundles and Chains
As well, it may be necessary to compose a certificate chain file, for the host, instead of a simple crt file.
Doing so, is required for Nginx and some mobile apps, as both require the CA authority certs to be in the same file as the host certificate.
To create a chain certificate, do this:
```bash
cat cert-start.pem ca-bundle.pem > full_chain.pem
```
## Pem to Crt
To convert the cert file (from pem) to crt, do this:
```bash
openssl x509 -outform der -in your-cert.pem -out your-cert.crt
```
## Pem to Key
To convert the private key (as pem) to key, do this:
```bash
openssl rsa -outform der -in private.pem -out private.key
```