By Christian Rentrop and Markus Will
One of the biggest clichés on the Internet is that emails are like postcards: can anyone read them on the go? and therefore confidential information should not be transmitted here. The reason for this is that an email is not simply exchanged between the sender and the recipient: on the way can it happen that it is routed through numerous servers and countries? even if the recipient lives in two houses next door. The reason: the big free mail providers like Google, Apple or Microsoft, but also many others, use American servers. When in doubt, the very general structure of the Internet secures the countless detours and servers along the way. Servers on which a malicious administrator can theoretically sit and intercept or read mail.Reason enough to think about email encryption.
Encrypt emails – here’s how
- Install an email program like Thunderbird, Apple Mail or Outlook.
- Set your email address there. You can get the configuration data from your mail provider, which usually has an FAQ section or a website like Gmail here https://support.google.com/mail/answer/7126229?hl=de, GMX here https : // help .gmx.net / pop-imap / imap / index.html or Microsoft Live here https://support.microsoft.com/de-de/help/287604/configure-outlook-to-connect-to- an-msn- Email account.
- Now download a GnuPG clientsuch as GPG4Win for Outlook CygWin, Enigmail or GPGTools for Mac.
- After installation, these programs offer the option of generating a key pair for each email address specified in the email client.
- You have to be a Enter password. This is meant to ensure that there is still protection in case the key falls into the wrong hands. You must be careful not to forget it, otherwise the key can no longer be used.
- Then you can use your Upload the public key to the key server. There is a worldwide group of network server PGP servers on which the public key is loaded for easy access. Now someone can send you an encrypted or signed message if they find your key there. You can also put the public key on your website or attach it to your emails.
- the You need to protect and secure your private keyso you can open this message. It is also recommended to keep the private key under lock and key and away from third parties, regardless of the computer. It is also important to create a revocation certificate. This is used if your key is compromised or the private key is no longer in your possession. This allows you to configure the key as “invalid” on PGP servers without having to use the private key. This avoids an “archive file”, since, in principle, the keys cannot be deleted there.
- the The OpenPGP program in the mail program recognizes itselfwhen you have received an encrypted email.
- You can send encrypted emails if you have the know the recipient’s public key. Modern GnuPG clients verify this automatically using the email address.
- You still have all the freedom: Just because you now have a PGP key doesn’t mean you have to encrypt all your mail.
This is why email encryption is so complicated
In theory, all emails are open.
In theory, encryption of emails is also a good thing: the sender encrypts the message with the recipient’s public key, only a chaos of characters is displayed along the way, and only the recipient can read the message with their private key and the proper password. decrypt. The so-called end-to-end encryption principle. Everything happens in virtually unbreakable RSA or AES encryption method. But what sounds so good in theory is not so easy in practice. On the one hand, both parties must already use PGP so that they can communicate in encrypted form (and this is not supported by default with Google, Apple, Microsoft and company, so you have to take action yourself and help yourself with the applications and plugins ). On the other hand, the sender doesn’t always know exactly if the recipient’s key is still up-to-date or if it belongs to the recipient. If you’ve avoided these cliffs and traded keys with the people you’re talking to, PGP is actually child’s play! Check the box here; enter a password there? And you communicate with NSA security!
GnuPG, OpenPGP, S / MIME …
But why is email encryption complicated? It starts with the fact that there are several standards: OpenPGP Y s / MIME are currently the most important. PGP emerged as the first process and when it became commercial, the free OpenPGP branch was developed, compatible with the original PGP, which is now used mainly by private users (if the article refers to PGP for simplicity, then it refers to OpenPGP) . s / MIME, on the other hand, is more of a commercial variant that requires official certification. In this article, therefore, we want to focus on the OpenPGP standard. GnuPG is a free Unix tool for email encryption using OpenPGP. Easy-to-use clients are available for Windows, Mac, and Linux systems (https://www.heise.de/download/product/gnu-privacy-guard-gnupg-1677). Additional applications for mobile devices are required: for example iPGMail on iOS and OpenKeychain and a suitable mail application such as K-9 Mailer or Kaiten on Android. In principle, email encryption is available on all major operating systems and end devices.
The thing about the key pairs
To get started, you first need one Create a key pair for your email account. This is very easy with the software tools: you specify the account to be encrypted and an encryption level, as well as a password. You can then receive encrypted messages or sign your mail. Signing means that the email is sent unencrypted, but the recipient recognizes by the signature that it really comes from you and that the content has not been tampered with. Encryption, on the other hand, encrypts the message completely, it is only readable if the recipient can decrypt it. And this is where key pairs come into play: There is one private and a public key. As the name suggests, the private key must remain private, that is, it must be on your computer. However, the public key is uploaded to a keyserver and can be accessed publicly.
Why this effort?
The principle behind this method is a asymmetric encryption method: The public key on the key server allows anyone to send you an encrypted message that only you can decrypt with your private key. Rather, this means that you can only send encrypted messages to people who have also created a key pair and uploaded a public key. Which makes the core problem of mail encryption also obvious: Emails can only be encrypted and decrypted between participants in the PGP / OpenPGP system ?? and if someone misplaces their private key or forgot their key password, they will no longer be able to read the message. Modern GnuPG clients can check if a public key is available, but they can’t check if the recipient is still using the tool and can decrypt their emails.
The identity thing
Another problem is that anyone can create keys ??? under each name and for each email address. The identity is practically not verified by the computer. This is where the “network of trust” comes in.. Public keys are “signed” to each other, thus creating a kind of “network trust”. You can do it in a personal exchange with your friends or business partners, or in a crypto party that is held precisely for the purpose of this mutual certification. In a broader context, c’t journal supports PGP / GPG through the free crypto campaign c ?? t. the c ?? t quasi-as a certificate authority (Certified Authority, CA) a high level of trustbecause he has been actively advocating for PGP / GPG for over 20 years. You can obtain a signature requesting certification and proving your identity by delivering the application in person with identification with a valid ID card or passport. If you add the Check the specified email address, you will receive a signatureso someone who doesn’t have a public key but knows the encryption campaign can tell by signing that you are who you say you are. To verify authenticity, the “fingerprint” (a unique number for each key) of the CA key from the encryption campaign is printed on the c’t print. You can apply at selected Heise fairs or events, or on Wednesdays between 4.30 pm and 5.30 pm at the Heise publishing house in Hannover. You can find more information about the encryption campaign here: https://www.heise.de/security/dienste/Krypto-Kampagne-2111.html
The webmail thing
Not all webmail users can use OpenPGP. Through Googlemail, OpenPGP is supported rather half-heartedly and explicitly unofficial with E2Email, and that’s exclusively through a Chrome plugin. On GMX and Web.de it looks much better. However, PGP can be used relatively conveniently through the Mailvelope plugin for Firefox and Chrome. However, due to operating system or software updates, it can happen over and over again that OpenPGP plugins do not work for a while until an update is available for them.
High technical obstacle
Technical hurdles and reasonable support from major email providers are the reasons why email encryption has not yet been widely accepted in the private sector. At least on the way between you and your mail provider, mail is protected on a small scale through Transport Layer Security, TLS for short. This has long been the norm with all common webmail providers in the browser. It is recognizable in small padlock on the url line: Your computer and the mail server negotiate an encryption that protects messages on the road.
You can also activate TLS in your email programif you are using a program like Apple Mail, Thunderbird, or Outlook. The advantage of this solution is that it always works ??? and requires no further configuration. TLS significantly increases the security of emails, but it is not as strong an encryption technology as OpenPGPbecause it does not cover the entire transport route. Until someone comes up with a simple, global implementation of mail encryption, the following applies: Take action yourself and seal your mail traffic against prying eyes or treat emails like postcards, then you have nothing to fear.