So it looks like a good way to send secure message is write them as text files, encrypt them via GPG and send as attachments. Am I right? On Mon, May 14, 2018 at 3:52 PM, Joseph Sinclair wrote: > The EFF recommendation is primarily an abundance of caution for the > community who use PGP for mail as many such users are at risk of serious > and targeted attack. > PGP being enabled won't open a threat vector for some other attack. > Having it enabled in email may, however, allow a targeted attack to expose > the decrypted content of those emails; so for now (if you have very > high-value encrypted emails) it may be better to export PGP email and > decrypt at the command line for reading in a text editor. > > TL;DR > Overall this is a class of attacks that could expose the plain text of > emails encrypted with S/MIME or PGP, but requires enough effort and skill > that it's mostly an issue for individuals who are using PGP or S/MIME to > defend against serious threats, such as criminal organizations or state > actors, and have emails containing sufficient value to justify the level of > effort involved. > All users should disable HTML in email by default, regardless, as that is > a major attack vector that has no known mitigation (and likely never will), > HTML may be enabled for individual (unencrypted) messages as needed. > Encrypted email should, of course, never be anything other than plain text > (with separately encrypted attachments if needed). > > Below is my (admittedly limited) full assessment for those who might be > interested. > > The vulnerabilities requires two major factors: > 1) The attacker must have the original encrypted message (the ciphertext) > still encrypted. These are most concerning as Man-in-the-Middle attacks. > 2) The client must (generally) have HTML email supported and enabled > (note, HTML isn't the only backchannel available, but it's the most likely > and by far the easiest to implement). > > Note that all of these techniques export some amount of the decrypted > data, but not a massive amount. Somewhere between 4 and 200 bytes. They > can be repeated, however, within a final multipart MIME email to obtain the > full text. > > How it works, in short form: > If you have HTML enabled on view, the attacker can send you a message in > HTML format with the ciphertext buried within the HTML (e.g. inside the > href attribute of a img tag), and use url packing (putting tracking text in > a URL after the resource path) to send that text to a server. The client > will happily decrypt the contents, then attempt to access the url, sending > the decrypted data to the server as part of the request. > If you have one of the HTML email clients (e.g. most webmail clients) that > allow script within the email, then a script could easily send the *entire* > decrypted content to the server, and then display *only* that to the user; > successfully hiding its tracks while obtaining the full decrypted message. > Webmail clients should probably never be used with PGP or S/MIME. > > What the attacker does is grab the encrypted message, modify it to take > advantage of one of the discussed techniques, and then forward it on to the > intended recipient. > In the simplest case, the attacker just wraps the content in properly > structured HTML (ideally with script) and adjusts the MIME structure, then > send it on. If HTML is enabled, this can be enough. > If a more advanced approach is required (and script isn't available), then > the data can be restructured in several ways using flaws in specific block > encryption modes (specifically CBC and CFB) to obtain small amounts of data > in each MIME part; repeating the attack enough times to get most or all of > the data (up to around 500 MIME parts). The message looks funny, and might > be suspicious, but it still has a decent chance of working. > With even more effort, a non-HTML backchannel might be used, something > like MIME external data blocks and DNS sniffing, or PGP key lookups, but > the amount of data obtained in this way will be quite limited. > > GPG includes certain mechanisms to prevent the more difficult attacks > against the OpenPGP specification, although it cannot do much about a leaky > client. Not all clients enable those features or respond to reported > security issues properly, however, so while GPG is (or can be) secure, its > use in email may not be, depending on the client. > Some mail gateways that apply encryption at the gateway are vulnerable, > although most can be configured to be secure, and some are secure in the > default configuration (details for these are not provided, of course). > > On 2018-05-14 01:58 PM, Herminio Hernandez, Jr. wrote: > > So this why the EFF is recommending this > > https://www.eff.org/deeplinks/2018/05/disabling-pgp-thunderbird-enigmail > > > > On Mon, May 14, 2018 at 1:24 PM, der.hans wrote: > > > >> moin moin, > >> > >> lots of news about "new" PGP and S/MIME handling security issues. > >> > >> Considering GnuPG addressed it 15 years ago, it doesn't seem to be new > :) > >> > >> Also, email clients automatically displaying remote content has never > >> been safe. > >> > >> Summary seems to be: > >> > >> 1. Using text mail rather than html mail mitigates one of the disclosed > >> issues. > >> > >> 2. Disabling old ciphers or having a mail client that properly handles > >> decryption warnings and/or sanitizes messages will work for the other. > >> > >> See mailpile's response for the latter. > >> > >> https://lists.gnupg.org/pipermail/gnupg-users/2018-May/060315.html > >> > >> https://www.mailpile.is/blog/2018-05-14_PGP_Security_Alert.html > >> > >> One good thing to come out of this is that I now know about mailpile :) > >> > >> ciao, > >> > >> der.hans > >> -- > >> # https://www.LuftHans.com https://www.PhxLinux.org > >> # Eternal vigilance is the price of liberty. -- Thomas Jefferson > >> --------------------------------------------------- > >> PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org > >> To subscribe, unsubscribe, or to change your mail settings: > >> http://lists.phxlinux.org/mailman/listinfo/plug-discuss > > > > > > > > --------------------------------------------------- > > PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org > > To subscribe, unsubscribe, or to change your mail settings: > > http://lists.phxlinux.org/mailman/listinfo/plug-discuss > > > > > --------------------------------------------------- > PLUG-discuss mailing list - PLUG-discuss@lists.phxlinux.org > To subscribe, unsubscribe, or to change your mail settings: > http://lists.phxlinux.org/mailman/listinfo/plug-discuss >