Not sure whether the "bug" (undocumented behavior) I encountered is common to other people, but this comment might save hours of painful debug:
If you can't generate a new private key using openssl_pkey_new() or openssl_csr_new(), your script hangs during the call of these functions and in case you specified a "private_key_bits" parameter, ensure that you cast the variable to an int. Took me ages to notice that.
<?php
$SSLcnf = array('config' => '/usr/local/nessy2/share/ssl/openssl.cnf',
'encrypt_key' => true,
'private_key_type' => OPENSSL_KEYTYPE_RSA,
'digest_alg' => 'sha1',
'x509_extensions' => 'v3_ca',
'private_key_bits' => $someVariable 'private_key_bits' => (int)$someVariable 'private_key_bits' => 512 );
?>