Testing SSL version

openssl s_client -connect -ssl3

Output if SSLv3 is disabled:

140412157757088:error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number:s3_pkt.c:339:


140003543803552:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:s3_pkt.c:1472:SSL alert number 40
140003543803552:error:1409E0E5:SSL routines:ssl3_write_bytes:ssl handshake failure:s3_pkt.c:656:

For SSLv2, use -ssl2 instead (requires custom build of OpenSSL)

Output if SSLv2 is disabled:

139642876688032:error:1407F0E5:SSL routines:ssl2_write:ssl handshake failure:s2_pkt.c:409:

PEM (base64-encoded DER)

Get information for a cert

openssl x509 -text -in /path/to/file.pem

Get information for a CSR

openssl req -noout -text -in /path/to/file.csr

Verify cert file

openssl verify /path/to/cert.pem
openssl verify -CAfile /path/to/ca-file.pem /path/to/file.pem

Verify cert on another server

openssl s_client -CAfile /path/to/ca-file.pem -connect


openssl s_client -CApath /etc/ssl/certs/ -connect

List the certificates on a remote server

openssl s_client -connect -showcerts

Verifying a private key matches a cert

openssl x509 -noout -text -in /path/to/file.pem
openssl rsa -noout -text -in /path/to/file.key

Make sure modulus and public exponents match, or:

openssl x509 -noout -modulus -in /path/to/file.pem | openssl md5
openssl rsa -noout -modulus -in /path/to/file.key | openssl md5

To check the CSR as well:

openssl req -noout -modulus -in /path/to/file.csr | openssl md5

Convert a certificate from PEM to DER

openssl x509 -in /path/to/file.pem -inform PEM -out /path/to/file.der -outform DER

Create a CSR and a new key

hostname=`hostname -f`; openssl req -sha256 -newkey rsa:2048 -keyout $hostname.key -subj "/C=GB/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=$hostname" -out $hostname.csr -nodes

Create a new key

openssl genrsa -out /path/to/file.key 2048

Create a CSR from an existing key

openssl req -sha256 -new -key /path/to/file.key -out /path/to/file.csr

Specify the subject when generating:

openssl req -sha256 -new -key /path/to/file.key -subj "/C=GB/ST=Berkshire/L=Newbury/O=My Company Ltd/" -out /path/to/file.csr

List the subject:

openssl req -noout -subject -in /path/to/file.csr

Create a self-signed cert with no passphrase

hostname=`hostname -f`; openssl req -x509 -sha256 -newkey rsa:2048 -keyout $hostname.key -subj "/CN=$hostname" -out $hostname.pem -days 7300 -nodes

Sign a CSR with another cert/key pair

openssl x509 -sha256 -req -in -out -CA cacert.pem -CAkey cakey.pem -CAcreateserial

DER (binary DER)

View detailed information about a DER cert

openssl x509 -inform der -text -in /path/to/cert.cer

Convert a DER cert to PEM

openssl x509 -inform der -in /path/to/cert.cer -out /path/to/cert.pem

PKCS #12 keystores

Creating a pkcs12 keystore from a PEM cert and key

openssl pkcs12 -export -inkey /path/to/file.key -in /path/to/file.pem -chain -CAfile /path/to/ca-file.pem -out `hostname -f`.p12
keytool -storetype pkcs12 -list -keystore /path/to/file.p12

Note: openssl often adds a readable comments before the key, keytool does not support that, so remove the openssl comments if they exist before importing the key using keytool.

Viewing info about a pkcs12 keystore

openssl pkcs12 -info -in /path/to/file.p12

Viewing valid dates of a pkcs12 keystore

openssl pkcs12 -info -in /path/to/file.p12 | openssl x509 -noout -dates

PKCS #7 keystores

Convert PKCS #7 keystore to PEM

This will output all of the certs in the PKCS #7 keystore into one PEM file:

openssl pkcs7 -print_certs -in certs.p7b -out certs.pem

If you get this error:

unable to load PKCS7 object

Try ading -inform der:

openssl pkcs7 -inform der -print_certs -in certs.p7b -out certs.pem

Certificate formats


PEM (technically base64-encoded DER)

  • Enclosed between -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----
  • Normally has a .pem extension, could have .cer, .crt, or .der extension
  • Default format for Apache, OpenLDAP

DER (technically binary DER)

  • Normally has .cer, .crt, or .der extension


  • A keystore archive normally containing a cert along with its key and often the other certs in the cert chain
  • Normally has .p7b or .p7c extension

PKCS #12 keystore

  • A keystore archive normally containing a cert along with its key and often the other certs in the cert chain
  • Normally has .p12 or .pfx extension (prefer .p12)
  • Default type for Windows certs