I recently upgrade to Fedora 20 and quickly found my offlineimap instance failing. I was getting all kinds of errors regarding the certificate not being authenticated. Concerned wasn’t really the word I’d use to describe my feelings around the subject. Turns out, the version of offlineimap in Fedora 20 (I won’t speculate as to earlier versions) requires a certificate fingerprint validation or a CA validation if
SSL=yes is in the configuration file (.offlineimaprc). I was able to remedy the situation by putting
sslcacertfile = /etc/ssl/certs/ca-bundle.crt in the config file.
I won’t speculate as to the functionality in earlier versions but checking to make sure the SSL certificate is valid is quite important (MITM). If you run across a similar problem just follow the instructions above and all should, once again, be right with the world.
I’ve been arguing with my web hosting company about their use of RC4. Like many enterprise networks they aren’t consistent across all their servers with respect to available ciphers and such. It appears that all customer servers support TLS_RSA_WITH_CAMELLIA_256_CBC_SHA and TLS_RSA_WITH_CAMELLIA_128_CBC_SHA, in addition to TLS_RSA_WITH_RC4_128_SHA (although the latter is preferred over the other two) but their backend controlling web servers only support RC4. This is a problem if you are handling crypto (keys) (and other settings) over a weak encryption path to better secure your web service as you have essentially failed due to using the weak encryption to begin with.
So what’s wrong with RC4?
It’s been known for a while (years!) that RC4 is not a good encryption cipher. It’s broken and there are several attacks that are available. So why is it being used so frequently? In a word: BEAST. RC4 was the only stream cipher available that can combat BEAST and so it became the standard for all TLS connections. It’s not clear which attack vector is worse: BEAST or the weak RC4.
In recent months most Internet browsers have implemented the workaround n/n-1 to fix the BEAST vulnerability. With the fix in place it should, once again, be safe to use block ciphers and, thus, get better encryption ciphers (better protection). There have been many people and organizations talking about the need to get rid of RC4 now since it is a bigger threat to web security. Yesterday Microsoft released a security bulletin discussing the problem and urged all developers to stop using RC4. (Oh yeah, and they also want to stop using SHA-1 as well.) I usually think of Microsoft as trailing in the security field (lets face it, their products aren’t known for being secure ever since that whole network thing happened) so when they say that this mess with RC4 must stop it’s gotten to a point where we should have already done so.
So what are we waiting for?
I think, simply, we’re waiting for TLSv1.1 and TLSv1.2 to become mainstream. It’s not as if these technologies have just popped up on our radar screens, however, (they’ve been out since April 2006 and August 2008, respectfully) but there has been slow adoption of the two flavors of TLS. According to Microsoft, their products are ready for TLSv1.1 and TLSv1.2 (both IIS on and IE 11+). Firefox supports up to TLSv1.2 in 25.0 but you have to manually turn it on (it’s for testing) and OpenSSL (used for Apache) should support TLSv1.2 in its 1.0.1e release. It’s time to start pushing these better encryption mechanisms into operation… now.
Thought I’d pass along this research study, The keys to the kingdom, as I found it to be quite interesting (especially when you scan the entire Internet for your data). If you don’t understand the math explanation at the beginning just continue reading as you don’t need to have a degree in math and science to understand what’s going on.
Since upgrading to Fedora 19 I’ve been working out the kinks. Today I was finally able to run one of my problems down and fix it. It involved the failure of my MTA to deliver mail due to a TLS failure.
This failure was working against both postfix and ssmtp. After much log searching I was able to determine that ssmtp wasn’t verifying the public certificate of the distance SMTP server against the CA certificates I have on my system. I was able to confirm that the problem existed on other Fedora 19 systems and that it wasn’t just my crazy setup. After working with a couple of developers it seems that the ssmtp configuration file now requires the entry “TLS_CA_File=/etc/pki/tls/certs/ca-bundle.crt” to function correctly. It is not currently known what changes were made that created this problem.
I have not troubleshot postfix as of yet but I suspect a similar solution will be needed.
I went to sign an outgoing message tonight and my Gemalto USB Shell Token wouldn’t light up when I plugged it into my USB port. After doing the typical troubleshooting I am left with the thought that the device has given up the ghost. This isn’t a big problem because I saved the card the SIM came out of and I’m able to use my token on my personal laptop with a traditional card reader. My work computer, however, does not have one of these fancy card readers (maybe I can find my USB one somewhere?).
I can buy another Gemalto device but I’m wondering if there is a better device to use? I mean, the Gemalto lasted almost 500 signatures. But I guess I can now take advantage of the failure to try something else. Does anyone have any suggestions?
Much of our daily lives are contained within our smartphones and computers. Email, text messages, and phone calls all contain bits and pieces of information that, in the wrong hands, could harm our privacy. Unfortunately many people either don’t understand how vulnerable their data is when sent across the Internet (or another commercial circuit) or just don’t care. While I don’t have much to say for the crowd in the latter category (can’t fix stupid) I do try to help people in the prior category understand that any network outside of their control is fair game for pilfering and that basic protections need to be taken to protect themselves. While I’m not going to dig into how data can be intercepted (there are plenty of articles out there on the subject) I would like to talk about how one can use tools to protect their data when using an Android smartphone.
Until recently email was the only easily-encrypted mode of communication. Most people didn’t have the means of encrypting their phone conversations and certainly not their SMS messages (unless you happen to be using a SME-PED, but those things are terrible in other ways). Now, Whisper Systems have released two open source programs that allow you to protect your communications. The first is called “RedPhone”. This program encrypts your phone conversations and allows you to converse securely. The second program is called “TextSecure” and encrypts text messages using authenticated, asymmetrical encryption.
I like the way TextSecure manages keys and allows you to verify the user’s key directly so you can establish trust. RedPhone appears to use the trust in the phone number for authentication. RedPhone also provides encryption opportunities when the distant party also has RedPhone on their device which is a nice feature that I wish TextSecure also provided. Both of these programs are very easy to use and need very little configuration.
TextSecure also provides an encrypted container for all your text messages so that your text messages are secure if the attacker has physical access to the device.
And OpenPGP is still a great option for protecting your email communications but that is a topic for later.
If your email messages are being signed using SHA-1 you may not be getting the security you think you are. Attacks on the hashing algorithm have caused much pain to those that use it. Luckily SHA-2 is available and hopefully we’ll start seeing SHA-3 out in the world soon.
You’ve probably already seen SHA-2 in the wild designated as SHA-224, SHA-256, SHA-384, and SHA-512. Because of the weaknesses found in SHA-1 it’s important to not use that algorithm any longer. That means when you generate hashes you shouldn’t use sha1sum but rather one of the SHA-2 tools: sha224sum, sha256sum, sha384sum, or sha512sum. Depending on the length of time you need to protect the data the strength of the hash will be important. A larger key will be more secure for a longer period of time than a shorter one.
GNU Privacy Guard (GPG) has a default of using SHA-1, however, unless you manually select another algorithm in your gpg.conf file (usually found in ~/.gnupg). To use something other than the default you should add the following lines:
personal-cipher-preferences AES256 TWOFISH AES192 AES personal-digest-preferences SHA512 SHA384 SHA256 personal-compress-preferences ZLIB BZIP2 ZIP
These lines establish not only the preferences for which algorithms to use (for cipher, digest (hashing), and compression) but also in what order to use them. You can determine what algorithms are available to you by asking GPG in the command line:
$ gpg --version ... Home: ~/.gnupg Supported algorithms: Pubkey: RSA, ELG, DSA Cipher: 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH, CAMELLIA128, CAMELLIA192, CAMELLIA256 Hash: MD5, SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224 Compression: Uncompressed, ZIP, ZLIB, BZIP2
GPG will show specifically what is supported based on what’s built into the code when the package was built.
Using the proper algorithm is important for maintaining a secure communications environment so do your research and use something in which you feel comfortable.