Digital document signatures
Many spreadsheets published on this site carry digital signatures. The purpose of the signature is to allow the end user to decide whether they consider documents from this source trustworthy, and to permit Excel to open them and enable the macro functions on which the spreadsheet calculations depend.
The digital certificates are issued to Owen Duffy by Owen Duffy, ie they are issued to Owen Duffy and signed by a Certificate Authority (CA) of Owen Duffy.
If you wish to permit Excel to run the macros automatically, the easiest approach is to download and install the CA certificate, and enable execution of signed macros in Excel's Trust Centre.
To download and install the CA certificate, enter the URL http://owenduffy.net/owenduffy.cer into Microsoft Internet Explorer (do not use another browser for this purpose), and then follow the prompts to open and install the certificate.
SHA1 digests used in earlier certificates are deprecated in favor of SHA256 digests, and accordingly the latest CA certificate, document and executable signing are with a SHA256 certificate. At this time, none of the work is dual signed, so older operating systems might indicate the SHA256 certificates have problems, but the problem is lack of support for SHA256 certificates in those older platforms.
The older SHA1 CA certificate is at http://owenduffy.net/owenduffy-SHA1.cer .
As documents are reworked, I will resign older documents on the site using a current SHA256 signature certificate.