Archive for the ‘Integrity’ Category

Postfix Encryption

2015-03-12 3 comments

I’ve been tinkering with the encryption options in Postfix for a while.  Encryption between clients and their SMTP server and between SMTP servers is necessary to protect the to, from, and subject fields, along with the rest of the header, of an email.  The body of the message is also protected but it’s always better to utilize PGP or S/MIME cryptography to provide end-to-end protection; encryption between clients and SMTP servers doesn’t provide this.

As rolled out now, encryption between SMTP servers is opportunistic encryption and is generally not required.  While doing a review of my mail log I seem to be receiving most personal mail via some encrypted circuit while much of the mail coming out of listservs, like Yahoo! Groups, is not negotiating encryption on connect.  I’ve also noticed that some email providers actually run their incoming email through an external service, I suspect for spam control, before accepting the message into their servers.  Some of these spam services don’t support encryption making it difficult to protect mail in transit.

Postfix documentation is pretty decent.  The project seems to document most settings but sometimes they don’t actually put the entire picture together.  Encryption is one of those things where a complete picture is difficult to put together just by looking at a single page of documentation.

Postfix’s documentation on TLS is fairly complete.  What they miss on that page, forward security, must be found else where.  Until last night, I had missed that last page and now have fixed my configuration to include, what I consider, acceptable settings.

Here’s what I’ve got:

### TLS
# enable opportunistic TLS support in the SMTP server
smtpd_tls_security_level = may
smtpd_tls_eecdh_grade = ultra
tls_eecdh_strong_curve = prime256v1
tls_eecdh_ultra_curve = secp384r1
smtpd_tls_loglevel = 1
smtpd_tls_cert_file = /etc/pki/tls/certs/mail.crt
smtpd_tls_key_file = /etc/pki/tls/private/mail.key
smtpd_tls_CAfile = /etc/pki/tls/certs/mail-bundle.crt
smtpd_tls_session_cache_timeout = 3600s
smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache
smtpd_tls_received_header = yes
smtpd_tls_ask_ccert = yes
smtpd_tls_received_header = yes
tls_random_source = dev:/dev/urandom
#TLS Client
smtp_tls_security_level = may
smtp_tls_eecdh_grade = ultra
smtp_tls_loglevel = 1
smtp_tls_cert_file = /etc/pki/tls/certs/mail.crt
smtp_tls_key_file = /etc/pki/tls/private/mail.key
smtp_tls_CAfile = /etc/pki/tls/certs/mail-bundle.crt

submission inet n       –       –       –       –       smtpd
-o smtpd_tls_security_level=encrypt
-o smtpd_sasl_auth_enable=yes
-o smtpd_sasl_type=dovecot
-o smtpd_sasl_path=private/auth
-o smtpd_sasl_security_options=noanonymous

Those familiar with setting up TLS in Apache will notice a few differences here.  We haven’t defined ciphers or SSL protocols.  This is because this is opportunistic encryption.  We’re just happy if encryption happens, even using EXPORT ciphers, since the alternate is plaintext.  In a more controlled setting you could define the ciphers and protocols and enforce their use.  Until encryption becomes the norm on the Internet (and why shouldn’t it be?) I’ll have to stick with just begging for encrypted connections.

It should also be noted that client-to-SMTP server connections are forced to be encrypted in as seen in the submission portion.  This was a quick and dirty way of forcing encryption on the client side while allowing opportunistic encryption on the public (port 25) side.

It should be noted that ECC keys can be used with Postfix, which forces good ciphers and protocols, but most email servers have RSA keys established so problems could arise from that.  Dual keys can always be used to take advantage of both ECC and RSA.

As SSLLabs is for testing your web server’s encryption settings, so is CheckTLS for checking your SMTP encryption settings.  These tools are free and should be part of your regular security check of your infrastructure.

CERN cares about information security… what about you?

2015-03-08 Leave a comment

As a security engineer it’s usually difficult for me to endure many of dumb things companies do.  It’s quite sad when a company that prides itself on creating solutions for building internal solutions to protect customer data actually starts pushing its own data out to Google and other “solution” providers.  It’s as if they don’t actually believe in their own products and actually think that a contract will actually protect their data.

So it’s quite refreshing when you run across a group that actually gets information security.  Recently, I ran across the information security bulletins at CERN (particle physics is another interest of mine) and was excited to find a group that actually gets it.  They provide internal, secure solutions for getting their work done without using outside solutions such as Google, Apple, Microsoft, Amazon, and Dropbox cloud solutions (I wish more of the internal solutions were FOSS but…).  In fact, CERN feels externally-hosted solutions are a bad idea for both business and personal uses.  I concur.

Here is a sample of their infosec bulletins:

What about you?  Do you care about the security of your information?

Securing Secure Shell

2015-01-06 2 comments

I was passed an interesting article, this morning, regarding hardening secure shell (SSH) against poor crypto that can be a victim of cracking by the NSA and other entities.  The article is well written and discusses why the changes are necessary in light of recent Snowden file releases.

Automated configuration analysis for Mozilla’s TLS guidelines

2014-10-09 Leave a comment

My friend Hubert has been doing a lot of work to make better the world a little safer.  Glad he’s getting some recognition.  Here’s a great article on testing your server for proper SSL/TLS configurations.

Signing PGP keys

2014-06-21 2 comments

If you’ve recently completed a key signing party or have otherwise met up with other people and have exchanged key fingerprints and verified IDs, it’s now time to sign the keys you trust.  There are several different ways of completing this task and I’ll discuss two of them now.


CA Fire and Forget (caff) is a program that allows you to sign a bunch of keys (like you might have after a key signing party) very quickly.  It also adds a level of security to the signing process by forcing the other person to verify that they have both control over the email address provided and the key you signed.  The way caff does this is by encrypting the signature in an email and sending it to the person.  The person who receives the message must also decrypt the message and apply the signature themselves.  Once they sync their key with the key server the new signatures will appear for everyone.

$ gpg --keyserver hkp:// --refresh-key

There is some setup of caff that needs to be done prior but once you have it setup it’ll be good to go.

Installing caff

Installing caff is pretty easy although there might be a little trick.  In Fedora there isn’t a caff package.  Caff is actually in the pgp-tools package; other distros may have this named differently.

Using caff

Once you have caff installed and setup, you just need to tell caff what key IDs you would like to sign.  “man caff” will give you all the options but basically ‘caff -m no yes -u ‘ will sign all the keys listed after your key.  You will be asked to verify that you do want to sign the key and then caff will sign the key and mail it off.  The user will receive an email, per user id on the key, with instructions on importing the signature.

Signing a key with GnuPG

The other way of signing a PGP key is to use GnuPG.  Signing a key this way will simply add the signature to the key you have locally and then you’ll need to send those keys out to the key server.

Retrieving keys using GnuPG

The first thing that you have to do is pull the keys down from the keyserver.

$ gpg --keyserver hkp:// --recv-keys ...

Once you have received all the keys you can then sign them.  If someone’s key is not there you should probably contact them and ask them to add their key to the servers.  If they already have uploaded their key, it might take a couple of hours before it is sync’d everywhere.

Using GnuPG

Signing a key is pretty straightforward:

$ gpg --sign-key 1bb943db
pub 1024D/1BB943DB created: 2010-02-02 expires: never usage: SC 
 trust: unknown validity: unknown
sub 4096g/672557E6 created: 2010-02-02 expires: never usage: E 
[ unknown] (1). MariaDB Package Signing Key <>
[ unknown] (2) Daniel Bartholomew (Monty Program signing key) <>
Really sign all user IDs? (y/N) y
pub 1024D/1BB943DB created: 2010-02-02 expires: never usage: SC 
 trust: unknown validity: unknown
 Primary key fingerprint: 1993 69E5 404B D5FC 7D2F E43B CBCB 082A 1BB9 43DB
MariaDB Package Signing Key <>
 Daniel Bartholomew (Monty Program signing key) <>
Are you sure that you want to sign this key with your
key "Eric Harlan Christensen <>" (024BB3D1)
Really sign? (y/N) y

In the example I signed the MariaDB key with my key.  Once that is complete a simple:

gpg --keyserver hkp:// --send-key 1BB943DB

…will send the new signature to the key servers.

Categories: Integrity, OpenPGP

PGP Keysigning Event and CACert Assertion at SELF2014

2014-06-16 Leave a comment

SouthEast LinuxFest is happening this upcoming weekend.  I offered to host a PGP (I’ll substitute PGP for GPG, GnuPG, and other iterations) keysigning and CACert Assertion event and have been scheduled for 6:30 PM in the Red Hat Ballroom.  Since there is a little bit of planning needed on the part of the participant I’m writing this to help the event run smoothly.

Participating in the PGP Keysigning Event

If you haven’t already, generate your PGP keys.  Setting up your particular mail client (MUA) is more than what I’ll discuss here but there is plenty of resources on the Internet.  Send me ( – signed, preferably encrypted to 0x024BB3D1) the fingerprint of your PGP key no later than 3:00PM on Saturday afternoon.  If you don’t send me your fingerprint by that time you’ll be responsible for providing it to everyone at the keysigning event on paper.  Obtaining your key’s fingerprint can be done as follows:

$ gpg --fingerprint 024bb3d1
pub 4096R/024BB3D1 2011-08-11 [expires: 2015-01-01]
 Key fingerprint = 097C 82C3 52DF C64A 50C2 E3A3 8076 ABDE 024B B3D1
uid Eric Harlan Christensen <>
uid Eric "Sparks" Christensen <>
uid Eric "Sparks" Christensen <>
uid Eric "Sparks" Christensen <>
uid [jpeg image of size 2103]
uid Eric Harlan Christensen <>
sub 3072R/DCA167D5 2013-02-03 [expires: 2023-02-01]
sub 3072R/A9D8262F 2013-02-03 [expires: 2023-02-01]
sub 3072R/56EA1030 2013-02-03 [expires: 2023-02-01]

Just send me the “Key fingerprint” portion and your primary UID (name and email address) and I’ll include it on everyone’s handout.  You’ll need to bring your key fingerprint on paper for yourself to verify that what I’ve written on the paper is, indeed, correct.

At the event we’ll quickly do a read of all the key fingerprints and validate them as correct.  Then we’ll line up and do the ID check.  Be sure you bring a photo ID with you so that we can validate who you are with who you claim to be to the authorities.  People are generally okay with a driver’s license; some prefer a passport.  Ultimately it’s up to the individual what they will trust.

CACert Assertion

CACert is a free certificate authority that signs X509 certificates for use in servers, email clients, and code signing.  If you are interested in using CACert you need to go sign up for an account before the event.  Once you have established an account, login and select “US – WoT Form” from the CAP Forms on the right-side of the page.  Print a few of these forms and bring them with you (I hope to have a final count of the number of assurers that will be available but you’ll need one form per assurer).  You’ll need to present your ID to the assurer so they can verify who you are.  They will then award you points in the CACert system.


If you have any questions about the event feel free to ask them here (using a comment) or email me at

Generating a PGP key using GnuPG

2014-06-16 3 comments

Generating a PGP using GnuPG (GPG) is quite simple.  The following shows my recommendations for generating a PGP key today.

$ gpg --gen-key 
gpg (GnuPG) 1.4.16; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Please select what kind of key you want:
 (1) RSA and RSA (default)
 (2) DSA and Elgamal
 (3) DSA (sign only)
 (4) RSA (sign only)
Your selection? 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 3072
Requested keysize is 3072 bits
Please specify how long the key should be valid.
 0 = key does not expire
  = key expires in n days
 w = key expires in n weeks
 m = key expires in n months
 y = key expires in n years
Key is valid for? (0) 1y
Key expires at Tue 16 Jun 2015 10:32:06 AM EDT
Is this correct? (y/N) y
You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
 "Heinrich Heine (Der Dichter) <>"
Real name: Given Surname
Email address:
Comment: Example
You selected this USER-ID:
 "Given Surname (Example) <>"
Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
You need a Passphrase to protect your secret key.
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
gpg: key 2CFA0010 marked as ultimately trusted
public and secret key created and signed.
gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0 valid: 2 signed: 49 trust: 0-, 0q, 0n, 0m, 0f, 2u
gpg: depth: 1 valid: 49 signed: 60 trust: 48-, 0q, 0n, 0m, 1f, 0u
gpg: depth: 2 valid: 8 signed: 17 trust: 8-, 0q, 0n, 0m, 0f, 0u
gpg: next trustdb check due at 2014-09-09
pub 3072R/2CFA0010 2014-06-16 [expires: 2015-06-16]
 Key fingerprint = F81D 16F8 3750 307C D090 4DC1 4D05 E6EF 2CFA 0010
uid Given Surname (Example) <>
sub 3072R/48083419 2014-06-16 [expires: 2015-06-16]

The above shows the complete exchange between GPG and myself.  I’ll point out a couple of selections I made and explain why I made those choices.

Key type selection

I selected the default selection of two RSA keys.  The keys used for signing and encryption will both be RSA which is strong right now.  DSA has been proven to be weak in certain instances and should be avoided in this context.  I have no comment on ElGamal as I’ve not done research here.  Ultimately the choice is up to you.

Bit strength

I’ve selected 3072 instead of the default 2048 here.  I recommend this as the minimum bit strength as this provides 128 bits of security as compared to 112 bits of security with 2048.  128 bits of security should be secure beyond 2031 as per NIST SP 800-57, Part 1, Rev 3.

Key expiration

By default, I make my keys expire after a year.  This is a fail-safe and can be later modified before the expiration to extend the expiration another year.  This makes sure the key will self destruct if you ever lose control of it.

Identifying information

You’ll  now be asked to add your name and email address.  This should be self-explanatory.

Key revocation

Once you have completed your key generation now is the time to generate the key revocation file.  If you ever lose control of your key you should immediately upload this file to the public key servers so everyone using your key will know that it has [potentially] been compromised.  Once you’ve generated this revocation just keep it somewhere safe.  You can even print it out and keep it locked up somewhere.  It’s important to do this this ahead of time as you may not be able to do this later.  You’ll obviously want to substitute your own keyid for 2CFA0010.

$ gpg --gen-revoke 2CFA0010
sec 3072R/2CFA0010 2014-06-16 Given Surname (Example) <>
Create a revocation certificate for this key? (y/N) y
Please select the reason for the revocation:
 0 = No reason specified
 1 = Key has been compromised
 2 = Key is superseded
 3 = Key is no longer used
 Q = Cancel
(Probably you want to select 1 here)
Your decision? 1
Enter an optional description; end it with an empty line:
Reason for revocation: Key has been compromised
(No description given)
Is this okay? (y/N) y
You need a passphrase to unlock the secret key for
user: "Given Surname (Example) <>"
3072-bit RSA key, ID 2CFA0010, created 2014-06-16
ASCII armored output forced.
Revocation certificate created.
Please move it to a medium which you can hide away; if Mallory gets
access to this certificate he can use it to make your key unusable.
It is smart to print this certificate and store it away, just in case
your media become unreadable. But have some caution: The print system of
your machine might store the data and make it available to others!
Version: GnuPG v1
Comment: A revocation certificate should follow

Proper key storage

Generally speaking, your private PGP key is stored on your computer encrypted.  It is protected by your normal security measures of your computer and whatever password you set.  There is a better way.  Use a hardware security module (HSM) like a Yubikey Neo, OpenPGP card, or CryptoStick to protect  your private key from disclosure.

Publishing your public key

Now that you have your PGP keys you’ll want to publish your public key to the key servers so others can easily obtain it to validate your signatures.

$ gpg  --keyserver hkps:// --send-keys 2CFA0010

You’ll obviously want to substitute your own keyid for 2CFA0010.  This command will send your key to the SKS public key servers which will then replicate your key around the world in a few hours.



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