There is no single solution for keeping yourself safe online. Digital security isn’t about which tools you use; rather, it’s about understanding the threats you face and how you can counter those threats. To become more secure, you must determine what you need to protect, and whom you need to protect it from. Threats can change depending on where you’re located, what you’re doing, and whom you’re working with. Therefore, in order to determine what solutions will be best for you, you should conduct a threat modeling assessment.

Now, Let’s Practice Threat Modeling

If you want to keep your house and possessions safe, here are a few questions you might ask:

• Should I lock my door?
• What kind of lock or locks should I invest in?
• Do I need a more advanced security system?
• What are the assets in this scenario?
  • The privacy of my home
  • The items inside my home
• What is the threat?
  • Someone could break in.
• What is the actual risk of someone breaking in? Is it likely?

Once you have asked yourself these questions, you are in a position to assess what measures to take. If your possessions are valuable, but the risk of a break-in is low, then you probably won’t want to invest too much money in a lock. On the other hand, if the risk is high, you’ll want to get the best locks on the market, and perhaps even add a security system.

All digital tools, whether they are hardware or software, should be secure. That is, they should protect you from surveillance, and stop your device from being controlled by others. Sadly, this is currently not the case. For many digital activities, you may end up needing dedicated programs or equipment intended to provide specific security features. Examples we use in this guide include software that allows you to encrypt your messages or files, like PGP.

But given the large number of companies and websites offering secure programs or hardware, how do you choose the one that's right for you?

How Transparent is it?

Even though digital security seems to be mostly about keeping secrets, there's a strong belief among security researchers that openness and transparency leads to more secure tools.

Much of the software used and recommended by the digital security community is free and open source, which is to say that the code that defines how it works is publicly available for others to examine, modify, and share. By being transparent about how their program works, the creators of these tools invite others to look for security flaws, and help improve the program.

Open software provides the opportunity for better security but does not guarantee it. The open source advantage relies in part on a community of technologists actually checking the code, which for small projects (and even for popular, complex ones) may be hard to achieve. When you're considering using a tool, see if its source code is available, and whether the code has an independent security audit to confirm the quality of its security. At the very least, software or hardware should have a detailed technical explanation of how it functions, for other experts to inspect.

What Happens if the Creators are Compromised?

When security toolmakers build software and hardware, they (just like you) must have a clear threat model. The best creators will explicitly describe what kind of attackers they can protect you from in their documentation.

But there's one attacker that many manufacturers do not want to think about: what if they, themselves, are compromised or decide to attack their own users. For instance, a court or government may compel a company to give up personal data or create a “backdoor” that will remove all the protections their tool offers. You may want to consider the jurisdiction(s) where the creators are based. If your threat is from the government of Iran, for example, a US-based company will be able to resist Iranian court orders, even if it must comply with US orders.

Even if a creator is able to resist government pressure, an attacker may attempt to achieve the same result by breaking into the toolmakers' own systems in order to attack its customers.

The most resilient tools are those that consider this as a possible attack, and are designed to defend against this. Look for language that asserts that a creator cannot access private data, rather than promises that a creator will not. Look for institutions with a reputation for fighting court orders for personal data.

Do you Know Others who Use the Same Tool?

It's a lot of work for one person to keep up with the latest news about a tool. If you have colleagues who use a particular product or service, work with them to stay abreast on what's happening.

Which Phone Should I Buy? Which Computer?

One of the most frequent questions asked of security trainers is “Should I buy Android or an iPhone?” or “Should I use a PC or a Mac?” or “What operating system should I use?” There are no simple answers to these questions. The relative safety of software and devices is constantly shifting as new flaws are discovered and old bugs are fixed. Companies may compete with each other to provide you with better security, or they may all be under pressure from governments to weaken that security.

Some general advice is almost always true, however. When you buy a device or an operating system, keep current with its software updates. Updates will often fix security problems in older code that attacks can exploit. Older phones and operating systems are no longer supported, even for security updates. In particular, Microsoft has made it clear that Windows XP and earlier Windows versions will not receive fixes for even severe security problems. If you use XP, you cannot expect it to be secure from attackers. (The same is true for OS X before 10.7.5 or "Lion").

When encryption is used properly, your communications or information should only be readable by you and the person or people you’re communicating with. End-to-end encryption protects your data from surveillance by third parties, but if you’re unsure about the identity of the person you’re talking to, its usefulness is limited. That’s where key verification comes in. By verifying public keys, you and the person with whom you’re communicating add another layer of protection to your conversation by confirming each other’s identities, allowing you to be that much more certain that you’re talking to the right person.

Key verification is a common feature of protocols that use end-to-end encryption, such as PGP and OTR. To verify keys without the risk of interference, it's advisable to use a secondary method of communicating other than the one you’re going to be encrypting; this is called out-of-band verification. For example, if you are verifying your OTR fingerprints, you might email your fingerprints to one another. In that example, email would be the secondary communications channel.

TextSecure is a messaging app that allows users to send confidential messages with their mobile phone using end-to-end encryption. The app works over a Wi-Fi or data connection, but can also be used to send SMS if such a connection is unavailable.

TextSecure can also be used to send SMS to non-TextSecure users, however, those messages will not be encrypted in transit. Encrypted text messages are marked with a small lock. Messages in blue are sent over a data connection, while those in green have been sent over SMS. Both sides have to be using TextSecure for the messages to be secure while they travel over the Internet. You can set up a passphrase that will encrypt these conversations when they are stored on your local phone. This means that they are better protected against being read if your phone is seized or compromised.

TextSecure is available in more than 30 languages. You can change the language of the app by selecting “Settings” then “Language.”

Verifying Keys

TextSecure uses end-to-end encryption. When you first send a message to another contact that uses the app, the app will initiate a key exchange message with the other user.

You will want to verify keys with the other user (for more information, view the module on Key Verification). To view the keys, click on the padlock icon in the top right of the screen and select “Verify Identity.” You will be shown two sets of keys: one belonging to you and one belonging to the other user.

TextSecure supports manual verification or verification by scanning the other user’s barcode. If you are in the same room as the other person, you can easily scan the barcode on their phone (reachable by clicking on the lock icon on the menu bar at the top of your conversation, selecting “verify identity” and then clicking on the barcode icon) or read your keys aloud to one another.

If you are not in the same room, there are different ways to verify keys with varying degrees of trustworthiness. For example, you can read your keys aloud to one another on the phone if you recognize one another’s voices or send them using another verified method of communication such as PGP or OTR.

PGP stands for Pretty Good Privacy. It's actually very good privacy. If used correctly, it can protect the contents of your messages, text, and even files from being understood even by well-funded government surveillance programs. When Edward Snowden says “encryption works,” it's PGP and its related software that he is talking about. It should be noted that it's not unheard of for governments to steal private keys off of particular people's computers (by taking the computers away, or by putting malware on them using physical access or with phishing attacks), which undoes the protection and even allows for reading old mail. This is comparable to saying that you might have an unpickable lock on your door, but somebody might still be able to pickpocket you in the street for your key, then copy it and sneak it back into your pocket—and hence get into your house without even picking the lock.

Unfortunately, PGP is also pretty bad at being easy to understand, or use. The strong encryption that PGP uses—public key encryption—is ingenious, but hard to wrap your head around. PGP software itself has been around since 1991, which makes it the same vintage as the early versions of Microsoft Windows, and its appearance hasn't changed much since then.

The good news is that there are many programs available now which can hide the ancient design of PGP and make it somewhat easier to use, especially when it comes to encrypting and authenticating email—the main use of PGP. We've included guides to installing and operating this software elsewhere.

Before you play around with PGP or other programs that use it, though, it's worth spending a few minutes understanding the basics of public key encryption: what it can do for you, what it can't do, and when you should use it.

Sign of the Times

Public key cryptography gets rid of the problem of smuggling the decoding key to the person you want to send a message to, because that person already has the key. You just need to get hold of the matching public, encoding key, which the recipient can hand out to everyone, including spies. Because it's only useful for encoding a message, it is useless for anyone trying to decode the message.

But there's more! If you encode a message with a certain public key, it can only be decoded by the matching private key. But the opposite is also true. If you encode a message with a certain private key, it can only be decoded by its matching public key.

Why would this be useful? At first glance, there doesn't seem to be any advantage to making a secret message with your private key that everyone in the world (or at least, everyone who has your public key) can crack. But suppose I wrote a message that said “I promise to pay Aazul $100,” and then turned it into a secret message using my private key. Anyone could decode that message—but only one person could have written it: the person who has my private key. If I've done a good job keeping my private key safe, that means me, and only me. In effect, by encoding it with my private key, I've made sure that it could only have come from me. In other words, I've done the same thing with this digital message as we do when we sign a message in the real world.

Signing also makes messages tamper-proof. If someone tried to change that “I promise to pay Aazul $100” into “I promise to pay Bob $100,” they would not be able to re-sign it using my private key. So a signed message is guaranteed to originate from a certain source, and not be messed with in transit.

So public key cryptography lets you encrypt and send messages safely to anyone whose public key you know. If others know your public key, they can send you messages, which only you can decode. And if people know your public key, you can sign messages so that those people will know they could only have come from you. And if you know someone else's public key, you can decode a message signed by them, and know that it only came from them.

It should be clear by now that public key cryptography becomes more useful, the more people know your public key. It should also be apparent that you need to keep your private key very safe. If someone else gets a copy of your private key, they can pretend to be you, and sign messages claiming that they were written by you. PGP has a feature that lets you “revoke” a private key, and warn people it's no longer trustable, but it's not a great solution. The most important part of using a public key cryptography system is to guard your private key very carefully.

Advanced PGP: The Web of Trust

You may have spotted a potential flaw in how public key cryptography works. Suppose I started distributing a public key that I say belongs to Barack Obama. If people believed me, they might start sending secret messages to Barack, encrypted using the key. Or they might believe anything signed with that key is a sworn statement of Barack. This is quite rare, and yet it has actually happened to some people in real life, including to some of the authors of this document—some people writing to them have been fooled! (We don't know for sure in these instances whether or not some of the people who make the fake keys were really able to intercept the messages in transit and read them, or whether it was the equivalent of a prank to make it more inconvenient for people to have a secure conversation.)

Another sneaky attack is for an attacker to sit between two people talking online, eavesdropping on their entire conversation, and occasionally inserting the attackers own misleading messages into the conversation. Thanks to the design of the Internet as a system that ferries messages across many different computers and private parties, this attack is entirely possible. Under these conditions (called a “man-in-the-middle attack”), exchanging keys without prior agreement can get very risky. “Here's my key,” announces a person who sounds like Barack Obama, and sends you a public key file. But what's to say someone didn't wait until that moment, jam the transmission of Obama's key, and then insert his or her own?

How do we prove that a certain key really does belong to a certain person? One way is to get the key from them directly, but that's not much better than our original challenge of getting a secret key without someone spotting us. Still, people do exchange public keys when they meet, privately and at public cryptoparties.

PGP has a slightly better solution called the “web of trust.” In the web of trust, if I believe a key belongs to a certain person, I can sign that key, and then upload the key (and the signature) to the public key servers. These key servers will then pass out the signed keys to anyone who asks for them.

Roughly speaking, the more people who I trust that have signed a key, the more likely it is that I will believe that key really belongs to who it claims. PGP lets you sign other people's keys, and also lets you trust other signers, so that if they sign a key, your software will automatically believe that key is valid.

The web of trust comes with its own challenges, and organizations like EFF are currently investigating better solutions. But for now, if you want an alternative to handing keys to one another in person, using the web of trust and the public key server network are your best option.

Adium is a free and open source instant messaging client for OS X that allows you to chat with individuals across multiple chat protocols, including Google Hangouts, Yahoo! Messenger, Facebook chat, Windows Live Messenger, AIM, ICQ, and XMPP.

OTR (Off-the-record) is a protocol that allows people to have confidential conversations using the messaging tools they’re already familiar with. This should not be confused with Google's “Off the record,” which merely disables chat logging, and does not have encryption or verification capabilities. For Mac users, OTR comes built-in with the Adium client.

OTR employs end-to-end encryption. This means that you can use it to have conversations over services like Google Hangouts or Facebook without those companies ever having access to the contents of the conversations.  However, the fact that you are having a conversation is visible to the provider.

Limitations: When Should I Not Use Adium + OTR?

Technologists have a term to describe when a program or technology might be vulnerable to external attack: they say it has a large “attack surface.” Adium has a large attack surface. It is a complex program, which has not been written with security as a top priority. It almost certainly has bugs, some of which might be used by governments or even big companies to break into computers that are using it. Using Adium to encrypt your conversations is a great defense against the kind of untargeted dragnet surveillance that is used to spy on everyone's Internet conversations, but if you think you will be personally targeted by a well-resourced attacker (like a nation-state), you should consider stronger precautions, such as PGP-encrypted email.

How to Initiate an OTR Chat

Once you have signed in to one or more of your accounts, you can start using OTR.

Remember: In order to have a conversation using OTR, both people need to be using a chat program that supports OTR.

Step 1: Initiate an OTR Chat

First, identify someone who is using OTR, and initiate a conversation with them in Adium by double-clicking on their name. Once you have opened the chat window, you will see a small, open lock in the upper left-hand corner of the chat window. Click on the lock and select “Initiate Encrypted OTR Chat.”

Step 2: Verify Your Connection

Once you have initiated the chat and the other person has accepted the invitation, you will see the lock icon close; this is how you know that your chat is now encrypted (congratulations!) – But wait, there’s still another step!

At this time, you have initiated an unverified, encrypted chat. This means that while your communications are encrypted, you have not yet determined and verified the identity of the person you are chatting with. Unless you are in the same room and can see each other’s screens, it is important that you verify each other’s identities. For more information, read the module on Key Verification.

To verify another user’s identity using Adium, click again on the lock, and select “Verify.” You will be shown a window that displays both your key and the key of the other user. Some versions of Adium only support manual fingerprint verification. This means that, using some method, you and the person with whom you’re chatting will need to check to make sure that the keys that you are being shown by Adium match precisely.

The easiest way to do this is to read them aloud to one another in person, but that’s not always possible. There are different ways to accomplish this with varying degrees of trustworthiness. For example, you can read your keys aloud to one another on the phone if you recognize each other’s voices or send them using another verified method of communication such as PGP. Some people publicize their key on their website, Twitter account, or business card.

The most important thing is that you verify that every single letter and digit matches perfectly.

Step 3: Disable Logging

Now that you have initiated an encrypted chat and verified your chat partner’s identity, there’s one more thing you need to do. Unfortunately, Adium logs your OTR-encrypted chats by default, saving them to your hard drive. This means that, despite the fact that they’re encrypted, they are being saved in plain text on your hard drive.

To disable logging, click “Adium” in the menu at the top of your screen, then “Preferences.” In the new window, select “General” and then disable “Log messages” and “Log OTR-secured chats.” Remember, though, that you do not have control over the person with whom you are chatting—she could be logging or taking screenshots of your conversation, even if you yourself have disabled logging.

Your settings should now look like this:

Also, when Adium displays notifications of new messages, the contents of those messages may be logged by the OS X Notification Center. This means that while Adium leaves no trace of your communications on your own computer or your correspondent's, either your or their computer's version of OS X may preserve a record. To prevent this, you may want to disable notifications.

To do this, select "Events" in the Preferences window, and look for any entries that say "Display a notification." For each entry, expand it by clicking the gray triangle, and then click the newly-exposed line that say "Display a notification," then click the minus icon ("-") at the lower left to remove that line." If you are worried about records left on your computer, you should also turn on full-disk encryption, which will help protect this data from being obtained by a third party without your password.

What is OTR?

OTR (Off-the-record) is a protocol that allows people to have confidential conversations using the messaging tools they’re already familiar with. OTR provides this security by:

• encrypting your chats
• giving you a way to make sure that the person you are chatting with really is that person
• not allowing the server to log or otherwise access your conversations

This should not be confused with Google's “Off the record,” which merely disables chat logging, and does not have encryption or verification capabilities. While there are several ways to use OTR on Microsoft Windows, we have found the most consistent and easy-to-use tool to be the Pidgin chat client with the pidgin-otr plugin.

The instant messaging client for Windows PC, Pidgin, automatically logs conversations by default, however you do have the ability to disable this feature. That said, you do not have control over the person with whom you are chatting—she could be logging or taking screenshots of your conversation, even if you yourself have disabled logging.

Limitations: When Should I Not Use Pidgin + OTR?

Technologists have a term to describe when a program or technology might be vulnerable to external attack: they say it has a large “attack surface.” Pidgin has a large attack surface. It is a complex program, which has not been written with security as a top priority. It almost certainly has bugs, some of which might be used by governments or even big companies to break into computers that are using it. Using Pidgin to encrypt your conversations is a great defense against the kind of untargeted dragnet surveillance that is used to spy on everyone's Internet conversations, but if you think you will be personally targeted by a well-resourced attacker (like a nation-state), you should consider stronger precautions, such as PGP-encrypted email.

Getting OTR

You can get pidgin-otr, the OTR plugin for Pidgin, by downloading the installer from the OTR download page.

Click the “Downloads” tab to be taken to the “Downloads” section of the page. Click the “Win32 installer for pidgin” link.

Many browsers will ask you to confirm whether you want to download this file. Internet Explorer 11 shows a bar at the bottom of the browser window with an orange border.

For any browser, it is best to first save the file before proceeding, so click the “Save” button. By default, most browsers save downloaded files in the Downloads folder.

After downloading Pidgin and pidgin-otr you should have two new files in your Downloads folder:

Installing pidgin-otr

Go back to the Windows Explorer window and open and double-click on pidgin-otr-4.0.0-1.exe. You'll be asked if you want to allow the installation of this program. Click the “Yes” button.

A window opens up giving you a quick overview of the installation process. Click the “Next” button.

Now you get a license overview. Click the “I Agree” button.

You will see where pidgin-otr will be installed. Don't change this information. Click the “Install” button.

Finally, you’ll see the last window of the pidgin-otr installer. Click the “Finish” button.

Adding an Account

When Pidgin launches for the first time, you will see this welcome window giving you an option to add an account. Since you don't have an account configured yet, click the “Add” button.

Now you'll see the “Add Account” window. Pidgin is able to work with many chat systems, but we'll focus on XMPP, formerly known as Jabber.

At the Protocol entry, select the “XMPP” option.

At the Username entry, enter your XMPP username.

At the Domain entry, enter the domain of your XMPP account.

At the Password entry, enter your XMPP password.

Checking the box by the “Remember password” entry will make accessing your account easier. Be aware that by clicking “Remember password,” your password will be saved on the computer, making it accessible to anyone who may happen to access your computer. If this is a concern, do not check this box. You will then be required to enter your XMPP account password every time you start Pidgin.

Configuring the OTR Plugin

Now you will configure the OTR plugin so you can chat securely. Click the “Tools” menu and select the “Plugins” option.

Scroll down to the “Off-the-Record Messaging” option, and check the box. Click on the “Off-the-Record Messaging” entry and click the “Configure Plugin” button.

Now you will see the “Off-the-Record Messaging” configuration window. Notice that is says “No key present.” Click the “Generate” button.

Now a small window will open and generate a key. When it is done, click the “OK” button.

You'll see new information: a 40 character string of text, broken up into 5 groups of eight characters. This is your OTR fingerprint. Click the “Close” button.

Now click the “Close” button on the Plugins window.

Shared Secret

A shared secret is a line of text you and the person you want to chat have agreed to use ahead of time. You should have shared this in person and never have exchanged it over insecure channels such as email or Skype.

You and your buddy need to enter this text together. Click the “Authenticate” button.

The shared secret verification is useful if you and your buddy have already made arrangements to chat in the future but haven't yet created OTR fingerprints on the computer you are using. This only works if both of you are using Pidgin.

Question and Answer

Question and answer verification is useful if you know your buddy but have not established a shared secret nor had a chance to share fingerprints. This method is useful to establish verification based on something both of you know, like a shared event or memory. This only works if both of you are using Pidgin.

Enter the question you want to ask. Don't make it so simple that someone can guess it easily, but don't make it impossible. An example of a good question would be “Where did we go for dinner in Minneapolis?” And example of a bad question would be “Can you buy apples in Tokyo?”

The answers must match exactly; so keep that in mind when choosing an answer to your question. Capitalization matters, so you might consider a note in parentheses like (for example: use capitals, lower case).

Enter the question and answer then click the “Authenticate” button.

Your buddy will have a window open with the question displayed asking for the answer. They will have to answer and click the “Authenticate” button. Then they will receive a message letting them know if the authentication was successful.

Once your buddy had completed the authentication procedure, you will get a window letting you know the authentication succeeded.

Your buddy should also verify your account so that both of you can be sure that the communication is secure. Here is what it would like for Akiko and Boris. Notice the green “Private” icons in the lower right of the chat window.