Why I am getting the "variable lookup failed for ca::default_ca" error when running OpenSSL "ca" command?

You are getting the "variable lookup failed for ca::default_ca" error, because OpenSSL "ca" command can not find the required "default_ca" option in the configuration file.

For example, if you have the follow configuration file, test.cnf, without "default_ca" option defined:

C:\Users\fyicenter>type test.cnf
# Unnamed section of generic options
default_md    = md5

You will get an error, because "default_ca" is a required option:

C:\Users\fyicenter>\local\OpenSSL-Win32\bin\openssl.exe

OpenSSL> ca -in test.csr -keyfile my_ca.key -cert my_ca.crt -config test.cnf
Using configuration from test.cnf
variable lookup failed for ca::default_ca
5956:error:0E06D06C:configuration file routines:NCONF_get_string:
   no value:.\crypto\conf\conf_lib.c:324:group=ca name=default_ca
error in ca

Fixing this error is easy. Just add the "default_ca" option in the unnamed section or in the [ca] section of the configuration file:

C:\Users\fyicenter>type test.cnf
# Unnamed section of generic options

# section for the "default_ca" option
[ca]
default_ca    = my_ca_default

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