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Hashing Email Addresses For Web Considered Harmful 155

cce writes "The MicroID standard, despite getting thrashed soundly by Ben Laurie two years ago, has since been recommended by the DataPortability Project and published on the user profiles of millions of users at Digg and MicroID is basically a hash calculated using a user's profile page URL and registered email address, producing a token that makes the email address vulnerable to dictionary attacks. To see how easy it was to crack these tokens, I conducted a small study, choosing 56,775 random Digg users, and cracking the email addresses of 14,294 of them (25%) using just their MicroID, username, and a list of popular email domains. Digg has more than 2 million users, and that means half a million of them — mostly people who had never heard of MicroID, and had probably not logged in for a long time — had their email addresses exposed to this trivial attack. I also applied this attack to (19%) and ClaimID (34%). Digg and have since removed support for MicroID, but the lesson is clear: don't publish a hash of my email address online, guys!"
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Hashing Email Addresses For Web Considered Harmful

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  • by pwnies ( 1034518 ) * <> on Thursday August 28, 2008 @07:01PM (#24786845) Homepage Journal
    I suppose this is yet another reason why it's nice that a few email services (most notably gmail) allow you to append a string to your email address using the + symbol (e.g. will go to the inbox of In effect it allows you to "salt" your email, which adds a layer of complexity when trying to match these hashes with valid email (not to mention it allows you to check which site compromised your email if you use different 'salts' for each site you use your address on). If more email services start to allow this (doubtful), more sites start realizing that a + in your email is still a valid email (more doubtful), and more users start using it effectively (even more doubtful still), then I don't think the MicroID will be a huge problem.
    • by nblender ( 741424 ) on Thursday August 28, 2008 @07:12PM (#24786965)
      + is a bad delimiter. Many web-forms don't accept email addresses with '+' in the username portion. Attempts to educate webmasters to the information in the relevant RFC's is usually met with silence or worse... I did manage to get a FOAF to fix though.
      • Re: (Score:3, Interesting)

        by Rinisari ( 521266 )

        Maybe that FOAF could attack, too. I tried registering there for a fantasy football league at work and used The damned system took the + out, making the address invalid!

      • Postfix Solution (Score:4, Interesting)

        by bill_mcgonigle ( 4333 ) * on Thursday August 28, 2008 @08:57PM (#24788187) Homepage Journal

        Assuming you're using postfix and virtual, you can do something like this:

        recipient_delimiter = +
        virtual_alias_maps = hash:/etc/postfix/virtual, regexp:/etc/postfix/virtual-regexp

        virtual-regexp: /(.*)\-(.*) ${1}+${2}

        and then you can do:


        this works for every site I've tried but, who apparently doesn't want you tracking their mail. :)

      • by mi ( 197448 ) <> on Thursday August 28, 2008 @09:34PM (#24788573) Homepage Journal

        + is a bad delimiter.

        It is the delimiter, originally created as such by the authors of the very first MTA []... There is no other character, that:

        1. Can be part of an e-mail address.
        2. Can not be part of a username.

        Many web-forms don't accept email addresses with '+' in the username portion. Attempts to educate webmasters to the information in the relevant RFC's is usually met with silence or worse...

        This is, unfortunately, the truth... Far too many programmer wannabees around... It is a good fight, however, and kudos to GMail for keeping support for it (unlike Yahoo! Mail).

        I use this whenever I can, when giving my address to web-sites (including Slashdot)...

        • "Can not be part of a username" is system-specific (and policy-specific) behavior. I don't allow hyphens, periods, underscores, or numbers in my usernames, and as such they are all valid delimiters.

          Depending on the number of users you have, how abusive they are, and how closely you monitor username selection it's entirely plausible to use a delimiter that *is* allowed in usernames, so long as you don't assign usernames that allow abuse.

          • by mi ( 197448 )

            depending on the number of users you have, how abusive they are [...]

            Well depending on how abusive you are, Mordac [], you may declare the letter "e" (the most frequently occuring in English) to be the separator — and punish attempts to use it as "abuse" by refusing service [] or worse.

            entirely plausible to use a delimiter that *is* allowed in usernames

            Sorry, I was talking about 99.99% of Unix installations out there. I did not account for yours... My post certainly was system-specific (no e-mail system tod

        • by synaptik ( 125 )

          Perhaps what we need is an RFC hall-of-shame... when we find websites that don't support the +, add their domain name to the roster.

          With enough promotion throughout geekdom, it could become such an embarrassing badge of dishonor that it evokes corrective action... similar to getting RBL'd for relaying spam (except that humans react to it, rather than MTA scripts.)

          Wishful thinking?

        • by kju ( 327 )

          There is no other character, that:
          1. Can be part of an e-mail address.
          2. Can not be part of a username.

          Untrue. The percent character can be used instead. While it was originally used for gateway-adressing, there is no reason not to use it instead for this subadressing. Both conditions are true for the percent character as well. The esclamation mark is another character which comes into mind.

        • by Sapphon ( 214287 )

          In fairness to Yahoo it should be mentioned that they do let you create what they call "disposable" e-mail addresses that work on the same principle: base_address-your_salt_here@yahoo.XYZ

          That solution may not be as easy or complete as GoogleMail's, but since the other big free e-mail provider out there (Hotmail) doesn't offer it at all, I don't think Yahoo is that bad.

          Now, if only they'd offer free IMAP *sigh*

        • It is the delimiter, originally created as such by the authors of the very first MTA

          But it didn't originate with Sendmail. The practice originated with qmail, and it's always been in qmail. Sendmail and Postfix added it in response to mail, and they obviously did it wrong.

          There's no reason you shouldn't use - except for the problem that crops up when you have a user named bob and another user named bob-foo which is that bob can't make a .qmail-foo that works. Never mind the fact that the administrator might

        • Re: (Score:3, Informative)

          by skeeto ( 1138903 )

          This is, unfortunately, the truth... Far too many programmer wannabees around...

          It is also unfortunate that perfect e-mail parsing is extremely complex. The Perl regexp for e-mail address validation according to RFC 822 [] is about 6.3 kilobytes []. If you try to do it yourself you are pretty much guaranteed to get it wrong.

          Those crappy programmers could still make things much better with liberal validation, allowing some invalid addresses to make validation simpler. Something simple like /[^@]+@[^@]+\.[^@]+/, will match all valid e-mail addresses (I think, and the /. filter won't let me

        • The problem is two fold.. browsers encoding a space " " to + instead of "%20", and servers that convert a + to a space again... solution would be to replace(trim(email_input), " ", "+") on the server-side form... That doesn't help the user for broken forms though.

          What we *NEED* is for the f-ing browser makers to encode a literal "+" from an input box to "%2B" ... since they're encoding spaces to the "+" sign.
      • Just use dots, then (Score:2, Informative)

        by Cow Jones ( 615566 )

        Apart from the fact "+" is a perfectly valid character in an email address, if you're using Gmail, you can insert random dots in your address, and your mail will still get delivered.

        is equivalent to

        • Make sure that it's not already in use by someone else. I have two GMail accounts, one for normal mail and one for mailing lists. The only difference between the two is that the second ends in ".ml" which would normally go to the main account, but since I registered the second one, it goes to that completely separate account.

          • Re: (Score:3, Informative)

            by funfail ( 970288 )

            This is completely different. What the grandparent said that "" would automatically go to "". Gmail just ignores dots in e-mail addresses.

      • by jez9999 ( 618189 )

        Attempts to educate webmasters to the information in the relevant RFC's is usually met with silence or worse

        What's worse than silence? They hunt down and kill your first-born? :-)

      • by Chyeld ( 713439 )

        gmail also ignores periods. is the same as or

        You can still salt without needing a +

    • by Anonymous Coward on Thursday August 28, 2008 @07:15PM (#24787001)

      Except that once the salted email is found, everything between the @ and the + will just be discarded.

      • it's a dictionary attack. user SugarBaby is Mel.Hopkins ok... Okay this is a little harder... we can't just apply names, now we have to apply an exhaustive space search.
      • by Tmack ( 593755 )
        If you are superparanoid, you can run your own mta, like qmail or postfix, and specify your own delimiter to regexp out of the address in one of the pre-processing filters. With qmail, I believe you could even just edit the qmail-smtpd config/run file (iirc, been a while) and add a pipe through sed to do the dirty work with the addy before the normal pipe through qmail.


        • Nah, if you're running qmail, just put a .qmail-something in your homedir containing the address to forward it to:

          Say you have:


          Makes this address forward to

          • by g0at ( 135364 )

            The same example and process apply for the Courier suite (a much better alternative to qmail ;)), though substitute ".courier" for ".qmail".


      • that would be up to the site admin to do that, not the attacker. and i see no reason for sites like Digg or to fuck with the e-mail address you input. if people find out that they are removing the +, then they will just lose security/privacy-conscious users.

    • Except that lots and lots of web sites fail at RFC 822 and think + isn't a valid character in an e-mail address. Usually the same sort of maldesigned horrors that make you type your e-mail address twice even though, unlike your password, you can read it as you type to make sure it's correct, or have a single free-form blank for credit card numbers and enforce some idiosyncratic rule on separators (really, is $cc =~ s/-//g; that hard?), or enforce strong passwords and then cripple them with mandatory 'security' questions that allow anyone who knows you halfway well to reset your password.

      Yeah, I use them too, and if web designers were a whole lot smarter they would be a better solution to things like this, but in practice lots of web sites just refuse to accept addresses like that. I should get around to making sendmail let me use an underscore instead of a + for that purpose.

      • or enforce strong passwords and then cripple them with mandatory 'security' questions that allow anyone who knows you halfway well to reset your password.

        How about sites that want "5-10 characters, only letters and numbers please"? Those are my personal favorites.

    • by statemachine ( 840641 ) on Thursday August 28, 2008 @07:55PM (#24787421)

      Giving out e-mails with "+something" is worthless for spam. The malicious spammers will just strip the "+something" from address, as both can be delivered, but the short form will be less likely filtered, and you won't know which service it was sold/stolen from.

      I actually make a separate alias for each site eg. If you shorten my alias to the part before the hyphen, it won't deliver. Yes, spammers have tried.

      If you're using "+something" just know that you might as well not append that onto your e-mail address, for all the good that it does, as you're giving out your primary address anyway. Cat, bag, already open.

      • Yeah, this can happen, but I dunno that this is as big a problem as you think. Spammers just plain aren't all that bright, and they don't care very much if they miss the tiny proportion of addresses that geeks try to protect like this when there are so many totally unprotected addresses so easy to obtain. It seems like a lot of the time, when they try to harvest addresses, the harvester doesn't realize + is a valid character in an address and only gets the part after the plus sign. I bounce a lot of spam sent to addresses like and

        • Re: (Score:3, Interesting)

          And the few times a harvester is correctly written? What then? That's the address that gets spread around. Obscurity doesn't work on the Internet. Just don't post it at all.

          But you seem fine with it because you're also posting your personal domain name here, which links to your name and your photo, along with a street address and phone number (which I hope are only P.O. box and a voicemail-only phone service). You're a hell of a lot more comfortable with it than I am. (At least I hope you knew that all that

          • by cduffy ( 652 ) <> on Thursday August 28, 2008 @08:52PM (#24788123)

            Obscurity doesn't work on the Internet.

            So why bother?

            Someone who was serious could get into public records and get my address anyhow (owning a house generates lots of public records). Someone who isn't serious presumably doesn't pose a threat. I think the worst thing that's actually likely to happen is 4chan-style harassment, and (1) it's not particularly likely, as I don't hang around those types enough for them to care about me, and (2) if it did happen, countermeasures are certainly available. And, again, (3) if anyone were serious enough about it, they could find all the relevant information through other channels anyhow.

            Being nymous online is a Good Thing -- it means people I know IRL can recognize me (I've run into ex-coworkers and old friends I didn't think I'd see again) and it gives me a chance to build a reputation that follows me into Real Life (so potential employers find plenty to recommend me when googling my name). Further, it acts counter to the tendency for anonymous communication to degrade into... well, you're on slashdot; you know exactly what I'm talking about. :)

            • (2) if it did happen, countermeasures are certainly available

              No, they're not. Not in the way that you think.

              1) Police are very limited in understanding and action with harassment crimes.
              2) Retaliating will likely get *you* into trouble, rather than the initial tard.
              3) Even if you do get a civil judgement, these people likely have nothing to lose. Therefore, you lose.
              4) Sending them to jail just makes them more pissed off. Then re-visit #3.

              In public forums like this, there are a lot of crazies on both sides of any argument. It's best to limit your exposure, unless you

              • by cduffy ( 652 )

                No, they're not. Not in the way that you think.

                Your guesses regarding what I think are inaccurate: my idea of a fun weekend is updating the rules for my asterisk server used to filter phone spam.

                To be sure, I don't particularly want to deal with cleaning up my credit report after some asshat decided to steal my identity in return for asking him to clean up his language in a public IRC channel... but hey, them's the risks with being out on the Internet these days, and (as before) I don't interact with those

                • Well, see, that's what you're comfortable with. ;) I prefer to be happy, which, as part of my definition, excludes all the crap you have to go through to protect yourself. Sure, what I do isn't perfect, but it's yet another several steps and guesses for someone to get to the point where I need to do what you're talking about. Why make it easy?

                  • Re: (Score:2, Interesting)

                    by cduffy ( 652 )

                    Hey -- we didn't arrange our schedules that way on purpose; it just happened as a happy accident. Likewise, I mess with Asterisk first and foremost because I think it's fun, and only secondarily because I dislike phone spam. (We did decide to do the large-dog thing as a security measure, but that was for late-night walks outside, not protection of the household proper -- and any weaponry we may have usable for home defense would have been purchased primary for recreational hunting; that said, I don't disclo

            • I don't know about you, but if I have an e-mail address listed on my resume that can be linked back to a fair amount of my internet doings.

              On the other hand, they cannot be linked to my /. account. Why? Because it wouldn't be a great idea if they could read all of my /. posts. Discriminatory hiring practices is illegal, but you need proof of that.

              That's my main reason for separating my profiles and keeping them separate. I'm sure law enforcement could, with the appropriate warrants, link everything back tog

        • by daeg ( 828071 ) on Thursday August 28, 2008 @09:42PM (#24788661)

          Spammers aren't bright? So spam filtering is easy, right?

          One (partial) solution is to have large providers provide alternate domains that you can register throw-away addresses. For instance, under Google Account settings, you might have the option to generate an address from and assign and allow you to record a note that you intend to use as your user ID.

          As time progresses, Gmail can show you stats that, for example, 100% of e-mail on is spam - "Do you want to delete this account?" and poof - the spam stops. Now that address automatically becomes a honey pot.

          • by mcrbids ( 148650 ) on Friday August 29, 2008 @12:46AM (#24790215) Journal

            Let's see... Large email provider, throwaway addresses, access until you don't want it anymore...

            You mean, kinda like Mailinator []??

            There are others, Mailinator is the easiest.

            • by houghi ( 78078 )

              I use a 'trow away address' that can be spammed all they want. I use it to subscribe to sites and then I just look what the link is to activate it and sometimes also use it to re-send something. is what I use.

              Some sites demand a new email address, as the old one must start paying. For those I make a new alias on my domain and as soon as I get the info, remove the alias again.

              I did use the and I noticed that it was way too much work to keep track of what to keep

      • by Z00L00K ( 682162 )

        Just consider that email addresses are a public affair.

        Sometimes you want a new email address for each service you register to and by that be able to track mail harvesters if you feel like that.

        The easiest way is to have a junk email address that you already get spam on when you register at various sites and then let the junk filter take care of the worst.

        And expect spammers to use a lot of various techniques to circumvent obfuscation. It's all about pattern matching - and adding a lot of standard names lik

    • Re: (Score:3, Informative)

      by aj50 ( 789101 )

      Except that some web forms (and some mail servers) won't accept an email address with a '+' in it.

      We use these types of addresses at work to organise replies to tickets and some people's mail set-ups really screw things up.

    • I used to do something similar on my personal mail server. What happened was that a few poorly-administered email lists had my raw address in that form in the public archives. So now my address ended up on spammer lists three multiple times, and I'd get the same spam on three "different" addresses at the same time.

    • by Builder ( 103701 )

      Many sites including Microsoft's Xbox site and TomTom do not accept the + sign as part of an e-mail address. This makes it worthless.

      Combined with Google Apps for Domains having allowing only a very small number of aliases, and we're back to having to run our own MTAs and dealing with all that grief, spam and wasted bandwidth :(

  • I've read up on it, but I don't understand how it benefits the user, vulnerability aside.
    • by Fred Ferrigno ( 122319 ) on Thursday August 28, 2008 @07:44PM (#24787301)

      I read up on it and I'm still confused, but I think this is the idea:

      1. You set up an account at website Alpha.
      2. You have a publicly-viewable profile page at Alpha. On the page is your MicroID.
      3. You set up an account at website Beta.
      4. You tell Beta about your Alpha profile page.
      5. Beta verifies that your Alpha profile page is really yours by checking the MicroID.

      Beta can't really do anything with your Alpha page except link to it. I guess the point would be to prevent people who aren't you from linking to your Alpha page on their Beta pages. That way, other people can be sure that the same person owns both accounts.

      The attack mentioned in the article doesn't compromise the proper use of the MicroID, since Beta is assumed to have verified that you own your email address and you wouldn't link to a profile page claiming to be yours that wasn't. All it does is make it possible for spammers to harvest your email.

      • by steevc ( 54110 )

        The attack doesn't compromise what MicroID does, which is to confirm that an account on a site is associated with a given email address. It's just a way of working out an email address from the MicroID hash.

        As long as it's not easy to guess your email from your name or you don't use a common provider then you are probably pretty safe.

      • Still confused as to how this is useful --

        The "ID" is just a hash -- in order to verify a hash, you re-generate it. So anyone who can verify your ID can also forge it.

        So then, how is this any better than "claiming" some element by just writing your name on it? It doesn't seem to do anything more substantial than just that.

        • So then, how is this any better than "claiming" some element by just writing your name on it?

          It isn't, really. The utility comes from Alpha only allowing people to write their own "name" (MicroID) on their page and Beta only allowing people to point to pages with their "name" on it.

  • To find out valid e-mails, couldn't a spammer just send out an e-mail blast to and throw away all the bounces?

    You wouldn't need a hash of any sort to do that kind of trivial attack and it isn't like the serious spammers are lacking in bandwidth or resources.

    • I do my own mail forwarding for a small domain that I own. There are about 20 valid email addresses at that domain. For the last year at least I have had a botnet harassing my mail server trying every conceivable random email address at my domain. I tried blocking by ip and iptables got so huge (10000+ ips) that it just about crashed my machine. I finally implemented gray listing so my machine just tells the botnet to buzz off and doesn't store any data but it's still an on-going problem. This whole bo

      • You might want to try OpenBSD's spamd in front of your machine. It can happily handle a few tens of thousands of connections on a moderate-spec machine. It is designed for very low CPU usage and replies to each greylisted connection insanely slowly. This means that it can take up to ten minute for a sending server to finish receiving the bounce notification. It ties up spambots quite effectively and stops them hammering your mail server.
  • Slashdot uses an e-mail scheme like that. Yeah, there it is, right there ^^^.
  • by RevDigger ( 4288 ) <> on Thursday August 28, 2008 @07:23PM (#24787075) Homepage

    This concern that you may have your email address *discovered* by spammers because you post it on a web page is so 5-years-ago. They already have your email address, and they probably didn't get it by scraping web pages.

    When you have sent a couple emails out with a given address, you can figure that at least one of them will to sit around in someone's Outlook mailstore for the next couple years. (Someone you know uses Windows!) When that person's computer gets infected with spam gang malware (as they all do), they have your address.

    Once of them has it, they probably all have it.

    • Re: (Score:3, Insightful)

      by John Hasler ( 414242 )

      > Once of them has it, they probably all have it.

      But they don't know that it is yours. They can spam you with it but they can't use it for anything else.

      • by oldspewey ( 1303305 ) on Thursday August 28, 2008 @09:04PM (#24788263)

        They can spam you with it but they can't use it for anything else

        Actually, in addition to spamming you, they can use your email address in the from and reply-to field for their next spam run.

        Ask me how I know.

        • Do you get hundreds or thousands of rejected emails a day too? I wish I could remember sending out all those advertisements for V1@GR4, or wishing people happiness in lyrical, non-sensical prose without actually trying to sell them anything.

          On a serious note, how many of those rejected emails are really from email servers with admins too stupid to not respond to spam, and how many are made to look like responses in the odd hope I really did forget I sent that email, and proceed to click on all the links
          • I have SPF records set with "-all" for all my domains, and only send mail out through my server, don't get many bounces at all anymore...
        • by u38cg ( 607297 )
          Because you've had non-stop backscatter for the last five years? Yeah me, too. At least until Russia rolled into Georgia, since when certain categories of spam have stopped entirely. Apart from chinese embroidery spam, which I do not understand at all.
      • by RevDigger ( 4288 )

        It may evolve to the point that these characters will want to invest the effort in really carefully targeting their marks. I have heard it called, "spear phishing," but I have never actually seen it.

        If they really wanted to do that, I would think they'd start by harvesting info from the million zombie pcs they root. I *have* seen a worm that eavesdropped on FTP to steal login info, and tag sites with malware, but that is about all I have seen in the wild.

        Most of the spam/phish gang action I see, seems to

      • Depends. If the user keeps their address book up to date then they also know your full name, address, telephone number, possibly date of birth, and so on. There were quite a few Outlook worms that allowed the author to gain full access to the address book.

        And you don't have to send the person email. Meet them, bluetooth your vcard to their phone. They go home and sync it with their Windows box, and all of that information goes in their address book. Then they get a worm / trojan and that information g

    • Re: (Score:2, Insightful)

      by cce ( 24686 )

      I'd argue that the added value of a spammer getting an email address connected to your online "identity" -- your user profile, recently-played songs, favorite Digg articles, etc -- makes getting your email from a MicroID a little more valuable than the ordinary harvested email address. Plus, they don't have to bother confirming the address to see if it's still active (Digg already did).

    • by eh2o ( 471262 )

      Yes!! Not only is it pointless to try to hide, the modern spam filter (e.g., gmail) is at least 99% effective. I put my email in plaintext and even in mailto: links all over the place and I have no serious problem with spam.

      Writing junk like foo [at] bar [dot] com simply wastes time time of your colleagues and friends, who now have to rewrite your address by hand, and confuses the non-techies.

      • Writing junk like foo [at] bar [dot] com simply wastes time time of your colleagues and friends, who now have to rewrite your address by hand, and confuses the non-techies.

        How dare you!? The hours I spend every week crafting clever rewrites of my email address is precisely that which keeps the spammers on their toes. How else do you think Gmail capable of filtering any spam mails out? I'm keeping their volume down. It's not just some stupid security superstition, either: it really works! And way better than whatever algorithm they're training over in Mountain View.

        From, [mailto]

    • I fully agree with the parent. The idea of keeping an email address that you actually use private is several orders of magnitude sillier than thinking your credit card number and social security number hasn't been stolen a dozen times already.

      But there is one place I won't "publish" my email address (, and that is in the From line of a Usenet posting. Reply-to is fine, and there absolutely no problem in the body of messages, but tests have shown that putting something in the From l

    • by Phroggy ( 441 )

      They're also still scraping e-mail addresses off the web. And no, just because one spammer has your address does NOT mean that all spammers have it: spammer #1 is not going to give your address to spammer #2 without compensation, so unless spammer #2 buys a collection of addresses from spammer #1 (they were going for about $500 for a database on CD-ROM last time I checked), or spammer #2 discovers your e-mail address independently, then no, spammer #2 doesn't have your address.

      • Or, #3, both have big lists and they exchange copies of them. I suppose this is a subcategory of #2, but you compensation doesn't have to be financial. If two spammers have lists of a million emails then they can swap them and get an even bigger list.
    • by steevc ( 54110 )

      Spammers got my main email ages ago and seem to have hacked a few forums for one-off addresses I used there too. So I don't worry too much about giving out my email address. The spam is mostly filtered, so I don't have to see it.

      I'm not sure exactly where they got my address from. It could have been on a keyserver. Searching for my address finds lots of hits on those. Much easier than trying to extract it from a MicroID. Those were potentially useful for proving identity.

      That said, spammers, identity thieve

  • This is exactly the reason I don't use Gravatar. They even tell everyone they are morons right here: []

    I didn't know anything about them except that someone in a forum was describing how you could have the same avatar in compatible forums that you participate in. The second I read that your hashed email address was part of the URL I turned around and never looked back knowing full well that if someone wanted to, they could eventually get my email address.

    • The second I read that your hashed email address was part of the URL I turned around and never looked back knowing full well that if someone wanted to, they could eventually get my email address.

      Erm, WTF?

      I don't like Gravatar either, as it's a centralized service, and one which frequently goes down.

      But you're afraid that, given a hash, someone can find your email address? Do you understand how hashing works?

  • The bottom line is that unless you don't have any online presence, your email address is going to leak, and it's going to wind up on spammer's lists. If you want to avoid getting spam, some other solution is called for.

  • I wrote about this earlier this year. [] My conclusion, more or less, was to carefully read the specification, which Iâ(TM)ll excerpt here:

    By itself, a MicroID has no inherent meaning, since it is simply a string created from two URIs. Any entity can generate a MicroID even if it has not verified the identity of the resources associated with one or both URIs. Furthermore, a MicroID is easily copied by an entity that did not generate it. Finally, a MicroID is not digitally signed by the entity that gen

  • Flawed study? (Score:2, Insightful)

    by dmuir ( 964412 )
    What's the difference between attacking the MicroID to collect email addresses, and running a dictionary attack on email servers using people's usernames?
    • Re:Flawed study? (Score:4, Informative)

      by QuantumG ( 50515 ) * <> on Thursday August 28, 2008 @08:22PM (#24787745) Homepage Journal

      Offline attacks are better because they:

      1. can't be monitored
      2. can't be blocked
      3. are not limited by bandwidth
      4. can be sped up by throwing more hardware at them

      This is basically why salting was added to the unix password file. And that failed.. so /etc/shadow was introduced. Revealing hashes is just unnecessary, so don't do it.

  • Personally, I can't get clients unless they know how to get in touch with me.

    And don't moan about spam. My E-mail address is widely published and maybe one or two messages a week gets through the filters.

  • I guess will now have to ecourage proxying of avatars via sites' web servers.

  • by Ed Avis ( 5917 ) <> on Friday August 29, 2008 @02:12AM (#24790763) Homepage

    You are worried because someone, if they really wanted to send you some mail, could go to the trouble of doing a CPU-intensive search against some hash shown on a website and find out that ultimate, embarassing secret: your *email address*??

    What gives? Email addresses are designed to be public. If you don't want people you do not know to be able to contact you, then you are free to drop all mail from unrecognized addresses. If you want to set up some kind of secret knowledge that people must have in order to contact you, then ask them to put a particular word in the subject line when first sending you a message. Either of these does not rely on keeping the address secret, which just isn't likely to happen.

    The only thing more broken than trying to keep an email address secret is trying to make a 'private' web page by keeping the URI secret. Again, the system is designed so that the address itself is not sensitive, but other information such as a password or PGP key can be.

    Actually, what it reminds me of most is the crazy situation in the US where a basically public identifier, the social security number, is abused as some kind of secret token. Hence all the fuss made when it is possible to find out someone's SSN. The answer is not to add more and more baroque means to stop the SSN from leaking out: one breach, and it's no longer a secret.

    I understand the desire to stop spam address harvesters, but really, there are hundreds of web sites which display email addresses with only light obfuscation, enough to stop a harvester bot but not a determined human being (or someone determined enough to use an OCR engine). The kind of hashing talked about here is way more difficult to undo than that. If you are even more paranoid, you need to revisit your assumptions of what is public and what is secret.

    • That may be fine for you but not everyone uses an email as a public contact point. In fact not everyone even lists their phone number.

      See the thing is, people have a funny way of deciding for themselves how they want to use technology (and, well, everything). And there really is nothing wrong with some people wanting a semi-private email.
  • by MisterBad ( 40316 ) on Saturday August 30, 2008 @12:24AM (#24806365) Homepage

    It seems like the attack is just taking user names and other publicly-known data trying to determine an email address from them. Spammers don't need microid to confirm that their guess is correct; they'll just send to all 50 or 100 top email domains, hoping to get a hit.

    The whole point of MicroID is that if someone knows your email address, they can tell that you are the author of the page. If your email address is easy to guess, then your email address will be revealed, _whether_or_not_ there's a microid here, there, or anywhere.

    If an email address is easy to guess, then the email address is easy to guess. Not clear what new ground we're covering here.

"If the code and the comments disagree, then both are probably wrong." -- Norm Schryer