The openssl program is basically a dumping ground for all sorts of SSL related functions. What it does varies wildly based on the parameters passed in. Here is a usage summary of some of the more useful functions.
| cert | Public X.509 format certificate. Contains subject's public key. |
| DER | Binary format used for keys |
| issuer | Entity that signs a cert |
| key | Subject's secret key |
| PEM | Straight ASCII (BASE64) format of a binary cert or key |
| sign | Calculate a secure hash and encrypt hash with issuer's private key |
| subject | The entity (person or organization) described in the cert |
| .pem | Stands for PEM, Privacy Enhanced Mail; it simply indicates a base64 encoding with header and footer lines. Mail traditionally only handles text, not binary which most cryptographic data is, so some kind of encoding is required to make the contents part of a mail message itself (rather than an encoded attachment). The contents of the PEM are detailed in the header and footer line - .pem itself doesn't specify a data type - just like .xml and .html do not specify the contents of a file, they just specify a specific encoding. |
| .key | Can be any kind of key, but usually it is the private key - OpenSSL can wrap private keys for all algorithms (RSA, DSA, EC) in a generic and standard PKCS#8 structure, but it also supports a separate 'legacy' structure for each algorithm, and both are still widely used even though the documentation has marked PKCS#8 as superior for almost 20 years; both can be stored as DER (binary) or PEM encoded, and both PEM and PKCS#8 DER can protect the key with password-based encryption or be left unencrypted. |
| .crt or .cer | Stands simply for certificate, usually an X509v3 certificate, again the encoding could be PEM or DER; a certificate contains the public key, but it contains much more information (most importantly the signature by the Certificate Authority over the data and public key, of course). |
| .csr or .req | Stands for Certificate Signing Request as defined in PKCS#10; it contains information such as the public key and common name required by a Certificate Authority to create and sign a certificate for the requester, the encoding could be PEM or DER (which is a binary encoding of an ASN.1 specified structure) |
openssl command [ command_opts ] [ command_args ]
| Standard Commands | |
|---|---|
| ca | Certificate Authority (CA) Management. |
| req | X.509 Certificate Signing Request (CSR) Management. |
| x509 | X.509 Certificate Data Management. |
| Digest Commands | |
| md5 | MD5 Digest |
| sha1 | SHA-1 Digest |
| sha256 | SHA-256 Digest |
| Common Options | |
|---|---|
| -config filename | Configuration file to use. |
| -nodes | Not the English word “nodes”, but rather is “no DES”. When given as an argument, it means OpenSSL will not encrypt the private key in a PKCS#12 file. To encrypt the private key, you can omit -nodes and your key will be encrypted with 3DES-CBC. To encrypt the key, OpenSSL prompts you for a password and it uses that password to generate an encryption key. |
| -key file | Use the private key contained in file |
| -keyform arg | Key file format |
| CA Options | |
| -in filename | Input filename containing a single certificate request to be signed by the CA. |
| -ss_cert filename | A single self-signed certificate to be signed by the CA. |
| -out filename | File to output certificates to. |
| -cert | The CA certificate file. |
| -selfsign | Issued certificates are to be signed with the key the certificate requests were signed with (given with -keyfile). |
| -days arg | The number of days to certify the certificate for. |
| REQ Options | |
| -inform arg | Input format - DER or PEM |
| -outform arg | Output format - DER or PEM |
| -in arg | Input file |
| -out arg | Output file |
| -pubkey | Output public key |
| -keyout arg | File to send the key to |
| -new | New request |
| -x509 | Output a x509 structure instead of a cert request |
| -days | Number of days a certificate generated by -x509 is valid for |
| -newkey rsa:bits | Generate a new RSA key of 'bits' in size |
| -text | Text form of request |
| -noout | Do not output REQ |
This just generates a matched pair of public and private keys using the RSA algorithm. Once generated these keys can be used for other SSL activities such as encryption certificate signing.
openssl genrsa -out my_key_name.key 2048
Both the public and private keys reside in the key file. Hold this file near and dear, especially if it isn't password protected. Extract the public key portion of this with RSA command.
openssl rsa -in my_key_name.key -outform PEM -pubout -out my_public_key_name.pem
openssl ca -new -x509 -extensions v3_ca -keyout CA-key.pem -out CA-cert.pem -days 3650 -config openssl.cnf -nodes
Here is a basic version of CSR generation
openssl req -days 3650 -nodes -new -x509 -keyout ca.key -out ca.crt -config openssl.config
Cheap SSL Security has a guide to CSR generation for Apache. They recommend:
openssl req -new -newkeys rsa:2048 -nodes -keyout baggerman.org.key -out baggerman.org.crt
This makes new RSA keys. To use an existing key use this form:
openssl req -new -key key_file_name.pem -out baggerman.org.csr
This doesn't seem to support Subject Alternative Names, though. Here is some good info on how to add SAN to openssl.conf. And here is a pretty good CSR builder that knows about SANs. Here is what needs to be added to the openssl.cnf file.
[ req ] req_extensions = v3_req # The extensions to add to a certificate request
[ v3_req ] subjectAltName = @alt_names
[alt_names] DNS.1 = www.baggerman.org DNS.2 = baggerman.org IP.1 = 198.89.126.181
Check the CSR with the following command:
openssl req -text -noout -in baggerman.org.csr
There is also a good CSR decoder at SSL Shopper
Use the .csr file to submit a signing request to a certificate provider like CheapSSL. Save the returned certificate into to a certificate file (.cer) Also save the intermediate certificate advisory file if necessary.
openssl ca -days 3650 -out key.crt -in key.csr -config openssl.cnf
openssl x509 -in certificate.crt -text -noout
openssl x509 -inform der -in certificate.cer -out certificate.pem
If you get an error it probably means the certificate is already in PEM format
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout mysitename.key -out mysitename.crt
Good notes at
Setup default SSL settings outside of a virtual host. Current recommended config (from https://cipherli.st/) is:
SSLCipherSuite EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH SSLProtocol All -SSLv2 -SSLv3 SSLHonorCipherOrder On
Be sure to set:
SSLCertificateKeyFile "/etc/pki/tls/private/csr.key" SSLCertificateFile "/etc/pki/tls/certs/web_server_cert.cer" SSLCertificateChainFile "/etc/pki/tls/certs/intermediate.pem"