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I've been asked by bankers, school administrators, insurance agents, car salesmen, realtors, you name it to send them all kinds of information over e-mail over the years. Everything from my address and phone number to credit card information and Social Security Number, either as text or in the form of scanned documents. Depending on the situation, sometimes I've said no, and sometimes I've said yes.

I know regular e-mail is insecure in theory while in transit, but not much more than that. A lot of times companies/people seem concerned only about convenience, so they make it hard to find other ways to send the information, like regular mail or faxing. So I'm wondering, is the danger in sending this information via e-mail much greater than the danger of those other ways?

I did a bit of homework before asking, and here's my current (but potentially flawed) understanding. There are two categories of vulnerability here, network sniffers at either endpoint and less-than-trustworthy servers on the route between the endpoints. From what I've read, it seems like the greater danger in practice is sniffers at endpoints (e.g. realtor checking mail on a public coffee shop network), although this is mitigated if people at both ends are on relatively safe (i.e. private) networks and/or using HTTPS-enabled webmail.

As for the other threat, I have a vague understanding of networking, and I wouldn't know where to begin getting control of machines that actually route e-mails between their start and end points. The danger there feels lower to me both because it seems more technically challenging and because such a machine would probably process a high volume of mail, so, "security" through obscurity might apply.

The alternatives are also hard to judge. Regular mail seems secure (if slow) but unless it goes to the final recipient, it might get scanned and insecurely e-mailed anyways. Faxing seems about as tangly as e-mailing, just over a different network, but probably harder for an attacker to "tap" in a useful way?

So, in addition to my main question above, I'd appreciate if you could correct any misconceptions I have there.

  • Related: security.stackexchange.com/q/67659/8411 – Ayesh K Dec 16 '14 at 19:38
  • There's also the "insider threat": your mail admin looking at things he shouldn't. – Mark Dec 17 '14 at 0:46
  • Welcome to the Sec.SE community, abby. Glad you popped over :-) – Rory Alsop Dec 18 '14 at 9:58
  • The difference between encrypting your email and not is more significant that between email and other mechanisms. – Chenmunka Dec 19 '14 at 14:28
  • hat me please! :) – user10211 Dec 21 '14 at 3:39
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Hopefully the mail traffic is encrypted via tls, but unless you administer your own mailserver there is no way to enforce this. To be shure your data is save you have to use pgp/gpg, bot many companies think that is too complicated for them. You must decide if you really want to do business with them if they are not prepared to safeguard your data. As a compromise maybe you can send a password protected zip file und exchange the password via a separate channel, e.g. a telefone call.

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Is the danger in sending this information via e-mail much greater than the danger of those other ways?

It's impossible to make qualified comparisons because there are many possible circumstances and variables. In general, however, unencrypted email security is similar to sending someone a post card: anyone who handles it along the way can read what it says. In the case of email, that would be any machine it passes through en route to its destination.

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As @geekamongus points out, there are risks associated with any communication method so direct comparisons are pretty hard.

However, there are several risks that cause me to not send sensitive communications via email. As the OP mentioned, there are problems with man-in-the-middle attacks at various stages of communication. An encrypted connection can help mitigate this risk, but only to a certain extent. Your email will only be protected in transit to the mail server that forwards your email through the internet. Once the forward happens, there is no guarantee that it is encrypted along the way outside special situations.

Faxes have their own set of problems, which include the ability to tap their communications (re: If I send a fax from an unsecure endpoint to a secure endpoint, is the data secure?), the machines sometimes having a memory of the last X number of faxes, internet services that sometimes convert faxes to PDFs automatically, and sometimes faxes end up running over VOIP instead of phone lines. The last two can result in insecure internet communication.

One issue encrypted connections do not address, and has not been mentioned so far, is the threat of the email sitting in the mailbox of the recipient. These other parties obviously do not take security very seriously, so who knows what compromises their systems may have, which may result in your sensitive information being read by some malicious party, or how often they leave their computer unlocked and unattended. You may also take the time to make sure it gets to them safely, and then they insecurely forward the email on to someone else.

Taking the time to encrypt your email before sending, as @UweBurger says, will mitigate the risk of interception being useful--assuming you use strong encryption--but is difficult to use. Explaining how to use PGP/GPG to a realtor would be a nightmare I imagine. A plus of this approach is it also will stymie mail administrators from reading the mail since you manually encrypted, and it would not necessarily be sitting on the other party's computer unencrypted either. Note that Google has created End-to-End (https://github.com/google/end-to-end) that attempts to make email encryption easier, but I haven't looked into its implementation to comment on its merits or issues.

In the end the decision is not black-and-white: you have to choose the right balance of security and ease-of-use that you're comfortable with.

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