Domain owner, admin-C and responsible
for the content on

Pe­ter Jockisch
Habs­bur­ger­stra­ße 11
79104 Frei­burg i.Br.

Telephone: +49 - 761 - 55 14 68

OpenPGP key ID, third and fourth quarter of 2012: FEE9A586
Key fingerprint: 4634 642B F48E E107 9C98 F368 CAE8 514F FEE9 A586
Validity period: May 16, 2011 through December 31, 2012

All content on is 100 % free of any charges, and directly available. Products or services are not offered. In the future, advertisement space will be rented out.

Photo: Peter Jockisch

Dear Site Visitors,

Thank you for your interest! I appreciate any feedback and constructive criticism.

If you would like to establish contact with me, please read the information below.

Peter Jockisch

Prefered communication medium: Cryptographically signed E-Mail

All of my e-mails are cryptographically signed with PGP/MIME or a separate signature. Without exception, I never send any unsigned e-mail. Signatures must be verified, with GnuPG (GNU Privacy Guard, www.​gnupg.​org, MS-Windows version:, for example. I only use the key with the listed data. Peter​ is the only official source for obtaining my key.

Signature verification with OpenPGP and GnuPG

To view a name and a cryptographical checksum, is not sufficient. For the authentication, the signature must be verified. After the initial activation, modern e-mail agents fully and automatically verify in the background.

For the qualified electronic signature, most often, only hardware-based (chip card) class-3-certificates, certified by legally recognized CAs are accepted by law. However, the required hardware and software infrastructure (available card readers, supported operating system, e-mail agent, software) is throughout of proprietary nature. This means not checkable and visible and thus, risky under security aspects. If attached to your email, I maybe will use such public X.509- or OpenPGP certificates with my MUA – However, I myself do not sign with such certificates

Cryptographical checksums as alternative proof of authenticity

Some recipients are not familiar with practical encryption and signing, or they have no possibility to use it in their country. In these cases, in addition to the signed e-mail, I write the message seperately in a “.txt” or “.pdf” file and publicize its checksum (SHA-1 or GOST) in the site blog section, combined with the date of dispatch, sending time and initials indicating the document.

For the verification, the checksum of the attached “txt”- respective “pdf”-file has to be created first. You can then look in the blog section of, if there is an entry with a corresponding checksum for the concerned e-mail sending day. There and only there are checksums of my e-mails publicized, nowhere else:, IP:

Use temporarily one of the official Firefox extensions, e.g. ShowIP, for letting you show the IP address.

My e-mail texts do not contain any data on the checksum. That would be completely senselessly. Everyone could write an arbitrary file and subsequently copy a checksum of the blog section into the e-mail text.

SSL/TLS certified site sections will follow.

The effective protection made possible by accessible cryptography technology is highly questionable, as real progressive computer technology is most probably held locked for the public, to always ensure the intelligence services of the ruling class a lead in computational power, and as probably software and hardware backdoors exist. However, the communications security can at least be increased within certain limits, through the systematic use of cryptographic signatures.

No representatives, no employees

I neither have representatives, nor assistants nor employees who speak for me. This will not change in the future. I do not offer any job.

No telephony, no mobile telephony, no fax

Principally, on a business level, I do not communicate by telephone which is unsuitable for proof of identity. Telephone information is principally not given. I do not own a mobile phone and no fax machine and I deny respective contracts or offers.

Due to telephony being unsuitable for proof of identity and the high risk of impersonation, I only conduct phone calls with immediate family using landline network only. I principally do not use mobile telephony, SMS and fax.

No advertising, no advertising e-mails/letters, no newsletters/products

None of my websites sends advertising e-mails.

I principally do not write reader's letters, and do not send any advertising e-mails, advertising letters, or newsletters. Current news and notifications can be obtained via RSS news tickers and can be read in news sections publicized on my official websites.

All information are offered exclusively “passive” on my own official websites, which can be seen in the imprint.

I neither use Twitter nor Facebook nor Myspace or other similar services.

All websites recommended by me are exclusively listed on, on Computer​ and on I do not practise banner exchange.

Official and solely Publication Platforms, Technical Aspects

I solely publicize on websites whose domains I own. My webhoster is Hetz­ner On­line AG, http://​www.​hetzner.​de/en. All my websites and content are being publicized exclusively via this webhoster. An exception to this is only my You­tube Channel, on which neither portrait photos nor computer articles are published.

Official and only used Websites

URL IP-Address Main Focus Language Personal site DE / EN Free articles on school mathematics DE Free articles on practical computing DE E-Books (under construction) DE / EN