How do I identify if my certificate contains private key?

Question

According to the answer to this server-fault question almost all certificate file formats can contain private key alongside public key, as such how can I identify whether a certificate contains private key?

This is important because I do not want to unknowingly send the private key to the remote client.

Answer 1

Following the structure of the link:

• .csr. Only public keys in pem or der format

• .pem. keys and/or certificates. Look for -----BEGIN PRIVATE KEY---- or -----BEGIN RSA PRIVATE KEY----- or -----BEGIN ENCRYPTED PRIVATE KEY-----

• .key keys in pem format

• .pkcs12 .pfx .p12 keys and/or certificates. List keys with openssl pkcs12 -info -nocerts -in keystore.p12

• .jks keys and/or certificates. Java specific format.

• .der pem content without base64 encoding. Look for KEY in openssl x509 -inform DER -in cert.der

• .cert .cer .crt keys and/or certificates. Content can be pem or der

• .p7b. Only certificates

• .crl. No keys