Digital Security For Journalists

Protecting Your Sources, Protecting Yourself

At the heart of most U.S. shield protections for journalists is a simple premise: If journalists cannot protect their sources, it substantially harms their ability to obtain the information they need to hold government accountable–perhaps the fundamental objective of a free and independent press. Given the current legal and technical realities, however, journalists who communicate with their sources digitally may be rendering these protections essentially moot. In practice the defaults on most email, chat, text, and telephone systems effectively identify our sources with every exchange, so protecting them means successfully scattering these digital traces so they cannot be used to connect the dots.

Of course, we work with many sources whose connection to us can be, and is, acceptably known, through long association or publication. Yet communication with these sources needs protecting too. As every journalist knows, sources sometimes don’t appreciate the implications of the information they share; ensuring confidentiality of their communications with us is an important part of source protection even if their identity is public.

Because of this, you’ll find the content below broken broadly into two sections: strategies for protected but linkable communications, followed by strategies for unlinkable communications. First, however, we’ll address the three main methods of digital information protection: encryption, obfuscation, and deletion.


Put simply, encryption is the process of scrambling or encoding messages in such a way that only someone with the correct “key” can unlock or unscramble the original.

In digital communications, there are two primary types of encryption: symmetric and asymmetric. In symmetric encryption, a single, secret key is used to both encrypt and decrypt a message. This approach is strong and fast, but requires that sender and recipient somehow agree on–and securely share–a single secret key. Symmetric encryption has been used for thousands of years and, at its heart, is very similar to the kinds of alphabetic substitutions that you might find on a decoder ring.

Asymmetric encryption, on the other hand, works by generating a mathematically related “public-private” key pair. Though each key can decode a message encrypted by the other, the two keys are asymmetric in the sense that the public key can be generated from the private key, but not the reverse. How is this possible? Asymmetric encryption takes advantage of the fact that it is generally much easier to mix things together than it is derive the original components from the finished product. For example, it is easy to create some color of green paint by mixing together yellow and blue. But the only way to tell what proportion of yellow and blue paints went into making a particular shade of green is through a long and arduous process of trial and error.

In mathematics, multiplication is fast, but factoring is time-consuming–even for a computer. The only way to find the factors of a number is to work your way up the number line, testing every possibility as you go. Public-private key pairs are based on this principle: The private key consists of a unique set of factors that when multiplied together yield the public key. Use enough factors–preferably prime numbers–in your private key, and it would take today’s computers decades or more to derive the private key from the public one.

These special properties of public-private key pairs let us do things with them that we cannot do with symmetric keys. For example, we can (as the name suggests) make the public key public, and claim it openly on the Web. Anyone who wants to send us an encrypted message can encode it with our public key, knowing that only the owner of the private key can decode it. Likewise, by sharing a message encoded with our private key, we let others verify that the public key we have indicated truly belongs to us. Of course, knowing that a person controls a particular key pair doesn’t actually tell you who they are. That step–confirming the “real” identity of the person who controls a particular key–is known as authentication.

For individuals, authentication can be done by securely sharing the hash (sometimes also called called a “fingerprint”) of your public key.

A typical PGP hash is 32 characters long.

Most simply, this can be done in person, via business card or QR code. Voice authentication is also a good option, since we tend to recognize individuals’ voices. Even postal mail can be an option, if you’re confident about where to physically reach the person with whom you’re trying to communicate. For websites, third parties vouch for the legitimacy of a public key by “signing” (or authenticating) it with their own. This is the equivalent of believing your friend when he or she gives you someone’s email address.

In practice, virtually all digital encryption systems are hybrid systems: They use both symmetric and asymmetric encryption. Typically, this means encrypting the actual message with a unique symmetric key, and then encrypting the symmetric key itself with the appropriate public key and transmitting it with the message. This is the process that underlies both secure (https) Internet connections and encrypted email.

A website’s “security certificate” is just another name for its public key.

There are cases, however, where no already-known “public key” is available to encrypt that symmetric key; when connecting to a wireless router, for example, or using many secure chat programs. For these, keys must be generated and exchanged on the fly, using a process called Diffie-Hellman key exchange.

For a helpful demonstration of this type of exchange, see Chris Bishop’s segment for the Royal Institution Christmas Lectures

Despite the fact the fact that the first messages are exchanged “in the clear,” this process makes it possible for both devices to derive the same shared secret key.

There is a vulnerability here, of course. How does one know that the first message really came from the person you think it did? If you had a public key to compare it to, it would be easy to check. Without this, however, it is possible that a third party could intercept your communications and impersonate each side to the other–all the while decrypting and reading all of the messages you exchange. This is known as the “Man in the Middle” (MITM) attack.

Fortunately, the MITM attack is simple to thwart: Simply telephone the person with whom you are chatting to verify that your secret keys match (many programs will display them on screen), or exchange it via encrypted email (provided you’ve already or authenticated that the public key you have really belongs to them). After that, you can chat with confidence.


Obfuscation is exactly what it sounds like: digitally “hiding” information, whether it’s data stored on your computer or your IP address on the Internet. Some forms of obfuscation also provide “plausible deniability”; in other words, the reasonable appearance that nothing is being hidden.

In general, obfuscation is difficult to do on one’s own; its effectiveness depends primarily on your data’s ability to “blend in.” For example, using “hidden volumes” to make an archive of sensitive documents look like a movie file works best if you have a reasonable number of movie files on your computer. That way, the chances of an attacker locating the one that is not actually a movie is much lower. Similarly, using a VPN or Tor to mask the geographic origin of your Internet traffic (addressed shortly) works best if there are many other users on the same system. In this sense, obfuscation can be best understood as a kind of herd protection, much like digital security in general. The bigger the crowd your data or operations can blend into, the more difficult it makes you and your sources to target.

One of the common challenges to the suggestion that more people use encryption is that there are environments where it makes one stand out, and thus a target for greater scrutiny. There are many cases where this is true. Obfuscation is exactly the principle of “security by obscurity,” which may actually mean forgoing encryption in certain contexts.


Ultimately, no kind of search can expose information you don’t have, both for individuals and service providers. Regularly and securely deleting unnecessary emails and files, especially from hosted services, is a simple and effective protection against having your data rifled through either by the authorities or by hackers. Think of this as cleaning out your file cabinet on a regular basis: Do it once every three months to help keep your exposure in check.

Recall that the contents of emails over 180 days old may be subject to subpoena, so doing this every six months is a minimum.

And remember that simply “trashing” your information isn’t enough. Online you’ll need to “delete forever,” and on your computer you’ll want to use a tool like CCleaner to truly overwrite “deleted” files so the data can’t be retrieved.