Skip to main content

Linux certificate storage

As opposed to Windows, Linux doesn't have crypto APIs that would be usable by user-mode applications. Linux does have Kernel level CryptoAPI (crypto.h) which is accessible to kernel mode processes. As such applications store certificates in application specific locations. That way we end up with multiple copies of the same certificate. One way to workaroud is to designate a directory for certificate storage and create symbolic links in required directories. 

The Linux Kernel Cryptographic API overview:

Generate CSR using a new key pair:

openssl req -nodes -newkey rsa:1024 -keyout serverName.key -out serverName.csr

Generate CSR using an existing key pair:

openssl req -new -key serverName.key -out serverName.csr

Once the request is signed, certs and keypair must be copied to relevant location. Most Linux applications require Base64 encoded certificate with .PEM extension. This however may vary. Apache for example requires Base64 encoded .CRT certificate. 

Sample storage locations:

Cisco AnyConnect:

User certs:

~/.cisco/certificates/ca                  Root CA
~/.cisco/certificates/client               User certificate 
~/.cisco/certificates/client/private       PrivateKeys

Computer certs:

/opt/.cisco/certificates/ca                    Root CA
/opt/.cisco/certificates/client                Client certificates 
/opt/.cisco/certificates/client/private    PrivateKeys




Locations of cert and private key are specified in the config file (sample config below) per virtual host. Sample location:


Enabling SSL in Apache. 

Enable mod_ssl:

# e2enmod ssl

Configure Virtual Host:

This is configured in an httpd.conf or apache2.conf (which by default includes httpd.conf)

DocumentRoot /var/www/
SSLEngine on
SSLCertificateFile /etc/apache2/conf/ssl.crt/
SSLCertificateKeyFile /etc/apache2/conf/ssl.key/

Restart  service:

# service httpd restart


# apachectl -restart


Popular posts from this blog

x.509 Certificates - Critical vs non-critical extensions

Extensions are used to associate additional information with the user or the key.  Each certificate extension has three attributes - extnID, critical, extnValue extnID - Extension ID - an OID that specifies the format and definitions of the extension critical - Critical flag - Boolean value extnValue - Extension value  Criticality flag specifies whether the information in an extension is important. If an application doesn't recognize the extension marked as critical, the certificate cannot be accepted. If an extension is not marked as critical (critical value False) it can be ignored by an application. In Windows, critical extensions are marked with a yellow exclamation mark,  View certificate extensions using OpenSSL: # openssl x509 -inform pem -in cert.pem -text -noout (output abbreviated)         X509v3 extensions:             X509v3 Key Usage: critical                 Digital Signature, Key Encipherment             X509v3 Subject Key Identifier

Cisco ASA Certificate Revocation Checking

ASA supports status verification using CRLs and OCSP. CRL can be retrieved using HTTP, LDAP or SCEP. Revocation checking using CRL: Over HTTP: ciscoasa(config)# crypto ca trustpoint ASDM_TrustPoint2 ciscoasa(config-ca-trustpoint)# revocation-check crl ciscoasa(config-ca-crl)# protocol http By default ASA will use address listed in CDP extension of the certificate that is being validated.  To override default behaviour we need to add the following in the CRL configuration context. ciscoasa(config-ca-crl)# policy static ciscoasa(config-ca-crl)# url 1 Over LDAP: Certificate I'm using for this lab, doesn't have LDAP address in its CDP extension. Therefore I'm using "policy static"  to specify LDAP URL where CRL can be retrieved.  ciscoasa(config)# crypto ca trustpoint ASDM_TrustPoint2 ciscoasa(config-ca-trustpoint)# revocation-check crl ciscoasa(config-ca-trustpoint)# crl configure ciscoasa

Count number of lines - 'findstr'

How do I count number of lines in a command output? findstr /r/n "^" | find /c ":" Above commands will display number of lines output by whatever command (well, nearly whatever) you specify in the front.  For example:  C:\>ping localhost | findstr /r/n "^" | find /c ":" FINDSTR: // ignored 12 This comes handy if you want to find out how many OUs you have in Active Directory: dsquery ou  -limit 0 | findstr /r/n "^" | find /c ":" How many user accounts there are: dsquery user -limit 0 | findstr /r/n "^" | find /c ":" Computers: dsquery computer -limit | findstr /r/n "^" | find /c ":"