Author image Dominique Quatravaux


Crypt::OpenSSL::CA::Resources - A bibliography of documentations and tools that I found helpful for implementing X509 PKIs in Perl over all these years.


For a tutorial introduction to the concepts of PKI and X509, please refer to the appropriate Wikipedia articles (in particular and

Have some giggles while uncovering the bleak truth about the state of affairs in PKI-world with Peter Gutmann's crypto tutorials at, and especially the one that deals with X509 PKI at


See Crypt::OpenSSL::CA::AlphabetSoup


X509 Style Guide

The X509 Style Guide, also by Peter Gutmann (, although partly outdated (e.g. as regards Unicode support) is the single most helpful resource one needs to develop and deploy a full-fledged X509 PKI.



A working, rugged implementation of "PKIX" in Crypt::OpenSSL::CA::AlphabetSoup that is GPL-licenced and covers all the bases, despite its being restricted from the "commercial" version. Definitely a reference implementation in the field (I know, since I helped write it!).


The venerable, feature-rich but quirky and poorly documented cryptographic library that Crypt::OpenSSL::CA is built upon. Available on (and also on, of course).


Of special interest is the /usr/bin/openssl command-line tool, that serves as a Swiss army knife of crypto debugging from making and parsing certificates to debugging SSL. Actually /usr/bin/openssl is powerful enough to serve as the sole foundation for a full-fledged PKI; this is almost what "IDX-PKI" does, but it is quirky (and therefore Crypt::OpenSSL::CA departs from that idea).

Here are a few tricks that I know by heart from typing them so often:

Parsing a certificate and displaying the details
  openssl x509 -noout -text -in cert.pem

or at an even lower level, using "dumpasn1":

  openssl x509 -outform der -in cert.pem | dumpasn1 -
Getting the modulus (unique public key identifier) of a certificate or private key

If both match, then the private key and certificate correspond to each other.

  openssl x509 -noout -modulus -in cert.pem
  openssl rsa -noout -modulus -in key.pem
Generating a self-signed certificate and matching private key for tests
  openssl req -x509 -nodes -new -newkey 1024 -keyout key.pem -out cert.pem

The resulting key.pem and cert.pem files can be used directly for a network server, or to build a toy CA.

Building a toy CA

Under distros that sport a cooperative openssl.cnf: this was tested on Ubuntu Edgy, your mileage may vary.

  1. create a test directory and chdir into it

  2. create subdirectories demoCA/private and demoCA/newcerts; put the string 01 into demoCA/serial; create an empty demoCA/index.txt file.

  3. create a key and a self-signed certificate for the CA as explained above, and save them respectively as demoCA/private/cakey.pem and demoCA/cacert.pem.

  4. create a certificate request using openssl req

  5. run

     openssl ca -subj "/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/CN=test" \
        -in user.req
  6. Rinse and repeat, tweaking the command line and the contents of the ./demoCA subdirectory until openssl is satisfied. Read the ca(3) man page to interpret and resolve the error messages.

  7. Your certificate should appear in ./demoCA/newcerts after a finite time (and tearing out only a minority subset of your hair).

  8. For advanced usage, copy over the default openssl.cnf file (usually to be found in /usr/lib/openssl, /usr/share/openssl or /etc/openssl) into demoCA and tack a -config ./openssl.cnf onto the openssl command line. Then you can start mucking with X509 extensions and so on.

Source code

Any serious work towards contributing to Crypt::OpenSSL::CA requires promiscuity with OpenSSL's code base. I suggest reading and understanding demos/mkcert.c and apps/ca.c first, comparing and contrasting with the XS code in Crypt::OpenSSL::CA which does roughly the same thing in a simpler and more modular way. Seasoned programmers will find the OpenSSL man pages of some limited help, and the command grep -r some_identifier /usr/include/openssl to come in handy more often than not.


There is a succint overview of OpenSSL's whole API in a file named doc/openssl.txt, to be found either in OpenSSL's source or possibly in the documentation directory of your distribution's openssl package (YMMV).


A tool to debug "ASN.1" in Crypt::OpenSSL::CA::AlphabetSoup data structures, more fault-tolerant than the openssl asn1parse command (see "OpenSSL"). Available on "Peter Gutmann's site" and as a Debian package.


Peter Gutmann's site contains more crypto- and security-related stuff, and is always a pleasure to waste office time reading from. and are both databases of "OID" in Crypt::OpenSSL::CA::AlphabetSoups that together contain pretty much all OIDs known to mankind. The latter sports a search engine.


The RFCs and other standards describing PKIX (the X509 PKI) are, in suggested reading order:


Basics, security model, definition of the entities (EE, RA, CA), format of messages between these entities (that nobody in his right mind would bother to implement in this contrived way).


Distinguished Names ("DN" in Crypt::OpenSSL::CA::AlphabetSoup)


Certificate and CRL formats, extensions in certificates, certificate validation algorithm.


How one should set the keyUsage bits in an X509 certificate.


Certificate request file format - One of the most popular ones (the great thing about standards, as the saying goes, is that there are so many to choose from...)


The other certificate request file format of importance to an Internet PKIX deployment ( Used by all browsers of the Netscape family.

The specification of the Netscape certificate type X509v3 extension. Mostly obsolete, but it does make your certificates all that more christmas-treeish.


A transport and backup format for X509 key material. Allows for bundling a user's certificate, its matching private key (password-protected), and the chain of CA certificates and CRLs that certify the user's certificate, all into a single binary blob.


"OCSP" in Crypt::OpenSSL::CA::AlphabetSoup


Qualified certificates.