Manipulating ssl certificates


Last updated 2017-12-14

SSL certificates are used in almost every network application to encrypt traffic to increase the safety of communications.

Manipulating ssl certs

Converting .crt to .pem

A .crt file can be identical to a .pem: They are both a b64-encoded block.

openssl x509 < rapidssl.crt -out rapidssl.pem

A .crt is usually the public key, and a .key is usually the private key.

Converting .crt set to a .pfx for Windows

Run each step separately because you might need to enter an import or export password. Use a simple password for each one for ease.

openssl pkcs12 -export -in wildcard-2016.crt -inkey wildcard-2016.key -out wildcard-2016.p12 -name wildcard -CAfile rapidssl-2016.crt -caname root
openssl pkcs12 -in wildcard-2016.p12 -out wildcard-2016.pem -nodes –clcerts
openssl x509 -in rapidssl-2016.crt -out rapidssl-2016.pem
cat wildcard-2016.pem rapidssl-2016.pem > wildcardchain-2016.pem
openssl pkcs12 -export -in wildcardchain-2016.pem -out wildcardchain-2016.pfx


Converting pkcs7 to pkcs12

openssl pkcs7 -print_certs -in crx.p7b | openssl pkcs12 -export -inkey crx.key -out crx.pfx -certfile crx.crt

Preparing hash file for ldap

Openldap can use ssl to encrypt its traffic, and the file needs to be rather specific. Around here, the /etc/openldap/ldap.conf file tends to have these directives:

URI ldaps://
BASE dc=example,dc=com
TLS_CACERTDIR /etc/openldap/cacerts

And in /etc/openldap/cacerts you might see these files:

4669ff29.0 -> authconfig.pem
authconfig.pem (the examplemicrosoft certs catted)

Observe that there is a hashed file as a symlink to the real cert file. Openldap will look for the hashed filename, whether it is a real file or just a symlink.
You can generate the hashed file by running c_rehash /etc/openldap/cacerts (or try cacertdir_rehash) from package openssl-perl or you can generate the symlink this way:

cd /etc/openldap/cacerts
ln -sf certs-example-2016.pem "$( openssl x509 -in certs-example-2016.pem -hash -noout ).0"

Reference: Weblink 2

Requesting a certificate signing

A CSR is for when you have a certificate you generated that you want signed by a certificate authority, whether that be the local CA or a public one.
You need a private key to start with, so the genrsa command will generate one.

openssl genrsa -aes256 -out wwwexamplecom-2016.key 2048
openssl req -new -key wwwexamplecom-2016.key -out wwwexamplecom-2016.csr
Enter pass phrase for wwwexamplecom-2016.key:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
Country Name (2 letter code) [XX]:US
State or Province Name (full name) []:Anystate
Locality Name (eg, city) [Default City]:Anytown
Organization Name (eg, company) [Default Company Ltd]:Example Company
Organizational Unit Name (eg, section) []:IT
Common Name (eg, your name or your server's hostname) []
Email Address []
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

Generally, don’t use a passphrase. If you must, do a simple one like linksys.

Send the csr to someone. This uses the script from bgscripts package. -hs "csr for" wwwexamplecom-2016.csr

Removing passphrase from private key

Apache in particular struggles with a private key protected with a passphrase. Apparently admins just leave the passphrase blank when generating a cert.
If you already applied one, and want to remove the passphrase, just use openssl.

openssl rsa -in old.key -out new.key

It will ask you for the passphrase, and then export the private key to the new file.

Adding AD certs to host trusted certificate store

Procure your AD root CA cert or download it from the certificate authority web portal, which could resemble Save as
Reference: Weblink 4

cp /etc/pki/ca-trust/source/anchors/

Reference: Weblink 5

Signing a certificate

Internal link 3 provides the certificate signing operations for Active Directory.

Adding key to java keystore

You might need to add a certificate to a java-like keystore. It is interesting to note that many java keystore files are actually symlinks to /etc/pki/java/cacerts.

/usr/lib/jvm/java/jre/bin/keytool -import -trustcacerts -alias "myaliasname" -storetype jks -keystore /usr/lib/jvm/java/jre/lib/security/cacerts -file ./comodo.cer -storepass changeit

Testing ssl cert from server

To find out if the https or other ssl-enabled service is serving the right certificate, you can use openssl as a client and pull down the ssl cert.

printf '\n' | openssl s_client -connect

And observe the output for the certificate information.
To test SNI, add the parameter -servername
Reference: weblink 6

Convert cer to pem format

openssl x509 -inform der -in certificate.cer -out certificate.pem

Reference: weblink 7

Read info from pkcs12 file

openssl pkcs12 -in cert.pfx -passin pass:'' -nodes -clcerts | openssl x509 -noout -subject -issuer -startdate -enddate

Delineate certificates in chain being served by a web connection

certchain="$( mktemp )" ; echo '' | openssl s_client -showcerts -connect > ${certchain} ; certcount=$( grep -cE '^-----BEGIN CERT' ${certchain} 2>/dev/null ); cat ${certchain} | { x=0 ; while test $x -lt ${certcount} ; do openssl x509 -noout -subject -issuer -dates ; x=$(( x + 1 )) ; done ; }



  1. Pkcs12 chained certificates demo:
  2. How to get the cert file hash without the c_rehash tool
  3. Removing passphrase from ssl key
  4. AD get root CA certificate
  8. The Most Common Java Keytool Keystore Commands

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