Monday, October 24, 2011

Android Command Line Dev with VI

Notes on developing Android apps from *NIX command line.

Building an Android application from the command line with VI can save time. Here are some notes on setting up Vim w/ tags and code completion for Android development. The relevant Ant commands for building Android apps from the command line are included. The example includes the commands for building and installing an Android app that links to a dependent java library which resides outside of the project source tree (in this case, the lvl lib), along with a C shared library that resides in the local jni/ directory.

Useful Vim Plugins for Android Development
  • Tag List
  • Nerd Tree
Setting up Vim JDE (vjde) requires a few configuration changes in order to work well with Android projects. First, download vjde.tgz version 2.6.18 from

Place vjde.tgz in $HOME/.vim and tar -zxvf vjde.tgz from within $HOME/.vim. Change the permissions on $HOME/.vim/plugin/vjde/readtags as follows:

$ chmod +x $HOME/.vim/plugin/vjde/readtags

Open an empty editor: $ vim and enter the following in command mode:
:helptags $HOME/.vim/doc

:h vjde
will then pull up the help page.

That should take care of setting up vjde. Now cd to the Android project dir. Open a blank editor and input the following in command mode:
:Vjdeas .myproject.prj
:let g:vjde_lib_path='/<path_to_android_sdk_top_level_dir>/platforms/ \

Next, Open up a source file in the project and type :Vjdeload .myproject.prj in command mode (or script and/or add to .vimrc). Use <ctrl-x><ctrl-u> for code completion. For example: import android.<ctrl-x><ctrl-u> and a nice little dialog box for browsing the matching frameworks.

Next, run ctags over the java and native sources as follows:
$ ctags -R src gen jni
Once NERD tree and Taglist are placed in ~/.vim/plugin/, the following lines in .vimrc will allow the use of <ctrl-n> and 
<ctrl-m> to toggle the file explorer and visual tag list.
nmap <silent> <c-n> :NERDTreeToggle<CR>
nnoremap <silent> <c-m> :TlistToggle<CR>
Also, for a status line:
set statusline=\ %{HasPaste()}%F%m%r%h\ %w\ \ CWD:\ %r%{CurDir()}%h\ \ \ Line:\ %l/%L:%c
function! CurDir()
let curdir = substitute(getcwd(), '/Users/myhomedir/', "~/", "g")
return curdir

function! HasPaste()
if &paste
return 'PASTE MODE '
return "
Vim should be good to go at this point. cd back to $HOME/src/myproject. This particular example accounts for a dependent Java library (the lvl) that resides outside of the project source tree, a shared library (which consists of a few C files natively compiled), and plain java source files in the appropriate src/com/ package subdir.

From within the top level project dir (assuming that Eclipse was used, otherwise, android create can be used ...),
$ android update project --name myproject --target <desired_sdk_target> \ --path $HOME/src/myproject
$ android update project --target <desired_sdk_target> --path $HOME/src/myproject \ --library ../lvl_lib_dir

Make sure to check to ensure that the android.library.reference.1 variable now contains the relative pathname of the lvl lib directory.

Assuming that jni/ and jni/ are appropriately setup for the shared library, run ndk-build from the top level project directory.
ant debug should now handle the build and debug version of the application package file.

Start up an Emulator and then install the app with a
db -r install bin/myproject-debug.apk or use ant install.
Next, open the Dev tools application in the emulator and configure the following: set wait for debugger and select the application for debugging.
Next, run ddms & and check the debug port. It should be 8700.
Subsequently, start the activity with
adb shell 'am start -n com.mycohname.myproject/.BaseActivityName'
And finally, connect via jdb from the shell with
$ jdb -sourcepath $HOME/src/myproject -attach localhost:8700
and start debugging.

Tuesday, September 6, 2011

Radius and 802.1X

Configure Radius and 802.1X.

1. Generate a new self-signed root CA, write the encrypted private key to CA/private/cakey.pem, and then write the Base-64,ASN.1-encoded, self-signed certificate to CA/cacert.pem.  This certificate will be used for signing client and server certificates.

# openssl req -new -x509 -extensions v3_ca -keyout CA/priv/cakey.pem -out CA/cacert.pem -days 730 -config openssl.cnf
# openssl x509 -in cacert.pem -noout -text
# openssl x509 -in cacert.pem -noout -dates
# openssl x509 -in cacert.pem -noout -purpose
# openssl x509 -in cacert.pem -noout -issuer
# openssl rsa -noout -modulus -in CA/priv/cakey.pem | openssl sha1
# openssl x509 -noout -modulus -in CA/cacert.pem | openssl sha1

Check the modulus and public exponent in the private key and certificate to make sure they match.

# openssl rsa -noout -modulus -in CA/priv/cakey.pem | openssl sha1
# openssl x509 -noout -modulus -in CA/cacert.pem | openssl sha1

2. Export the root CA signing certificate to ASN.1, DER encoded format so that clients can import it.

# openssl x509 -in CA/cacert.pem -outform DER -out clientCerts/myRootCA.der

2a. Convert the DER encoded CA back to pem format and place in a .crt file so that Android can read it. (This is an extra, un-needed step as cacert.pem can be copied and renamed to .crt). (Android does not understand pem files so write the DER encoded certificate to PEM format in a file with extension .crt).

# openssl x509 -inform der -in clientCerts/myRootCA.der -out clientCerts/myRootCA.crt

3. Generate radius server certificate (i.e. signing request) and private key in unencrypted format.

# openssl req -new -nodes -keyout tempCerts/radius_key.pem -out tempCerts/radius_req.pem -days 730 -config openssl.cnf

4. Sign the radius server certificate. note: Microsoft clients require the creation of an xpextensions file. Add '-extensions xpserver_ext -extfile ./xpextensions' to the following command.

# openssl ca -out tempCerts/radius_cert.pem -infiles tempCerts/radius_req.pem -config openssl.cnf

5. Install the root CA signing certificate, Radius server private key, and Radius server signed certificate.

# cp tempCerts/radius_cert.pem /etc/radwl/certs/server/
# cp tempCerts/radius_key.pem /etc/radwl/certs/server/
# cp CA/cacert.pem /etc/radwl/certs/server/

6. Create the client certificate (i.e. signing request) and private key. note: match the output file names with the client identity or common name.

# openssl req -new -keyout tempCerts/myandroid_key.pem -out tempCerts/myandroid_req.pem -days 730 -config openssl.cnf

7. Sign the client certificate.

# openssl ca -out tempCerts/myandroid_cert.pem -infiles tempCerts/myandroid_req.pem -config openssl.cnf

8. Export the signed client certificate and private key to pkcs#12 format.

# openssl pkcs12 -export -in tempCerts/myandroid_cert.pem -inkey tempCerts/myandroid_key.pem -out clientCerts/myandroid_cert.p12 -clcerts

9. Install the signed client certs on the Radius server.

# cp tempCerts/*_cert.pem /etc/radwl/certs/clients

10. Copy the client pkcs#12 certificate to appropriate device.

# cp clientCerts/myandroid_cert.p12 DEVICE

11. Copy the CA signing certificate to the same device.

# cp clientCerts/myRootCA.crt DEVICE

12. on OS X, use the following commands to add the freeradius user to the freeradius group. Also run chsh freeradius and set the shell to /sbin/nologin

# dscl . append /Groups/freeradius GroupMembership freeradius

Tuesday, August 16, 2011

OpenSSH Security - Client Configuration

OpenSSH provides a suite of tools for encrypting traffic between endpoints, port forwarding, IP tunneling, and authentication. The below instructions outline a client side OpenSSH configuration where the client is running on OS X. The built in firewall, ipfw, is enabled on the client to restrict outbound and inbound traffic. Part II (currently on hold) of this guide will cover the configuration of OpenSSH on the server along with the available options and alternatives for authentication, authorization, and traffic encryption. The configuration will force AES 256 in Counter Mode and will restrict the available Message Authentication Algorithms that may be used between endpoints. Most of the options in the ssh configuration file on the server will be disabled, public key authentication will be used, password authentication will be disabled, and the ssh daemon will bind to a high number port. Multiple SSH sessions will use the same connection via the ControlMaster and ControlPath client configuration directive. Also, a server certificate will be generated and used to sign user public keys. The CA signed user public keys constitute a user certificate which the server will in turn use for client authentication. PF will be used on the server for stateful packet filtering, connection blocking, and connection throttling. The below configuration will also detail

First and foremost, the client has ipfw enabled and the firewall ruleset is configured in /etc/ipfw.conf. ipfw has been configured to block all inbound traffic and block all outbound traffic except for the ports and IP addresses that are necessary for connecting to the OpenSSH server. The server is running FreeBSD 8.2.

FreeBSD 8.2 - sshd on a.b.c.d:21465 pf |  <--------Internet---------->  | ipfw  OS X Lion - ssh client
To start with, install coreutils and apg on the client. coreutils and apg can be obtained from Mac ports and can be installed as follows:

client: $ sudo port install coreutils 
client: $ sudo port install apg 

Before generating a public/private keypair, generate a strong passphrase for the private key. It is important to store this passphrase in a secure location, not on a computer.

client: $ openssl rand -base64 1000 | shasum-5.12 -a 512 | apg -M SNCL -a 1 -m 20 -x 20

Depending on the version of OpenSSH (should be using latest stable for the OS), ECDSA may be used in addition to DSA and RSA. Certificates may also be used for user and host authentication. See the ssh-keygen man page for details.  Generate the keypair using the following command. When prompted for the passphrase, use the output from the above command.

client: $ ssh-keygen -b 4096 -t rsa -C"$(id -un)@$hostname)-$(gdate --rfc-3339=date)"

Here is an example of how to use ssh-keygen to generate a public/private keypair using the Eliptic Curve Digital Signature Algorithm. Both the client and server must be running a version of OpenSSH >= 5.7.

client: $ ssh-keygen -b 521 -t ecdsa -C"$(id -un)@$hostname)-$(gdate --rfc-3339=date)"

Now, we need to push the public key to the server and place it in the authorized_keys file of the user that we are going to log in as over ssh.
The ssh-copy-id command can be used to automate this process. On the OS X client, the ssh-copy-id command does not come preinstalled with SSH. The ssh-copy-id command can be obtained from;content-type=text%2Fplain. After downloading the script, change its permissions and place it in the path.
At this point, the server should be running OpenSSH on port 22 with the default configuration. Transfer the public key with the following command:

client: $ ssh-copy-id -i ~/.ssh/ bryan@a.b.c.d \

It is time to setup connection sharing. Create the following file if it does not currently exist.

client: $ ls -l ~/.ssh/config -rw------- 1 bryan scclp 104 Aug 13 10:55 config

The file should contain these lines.

ServerAliveInterval 60 Host a.b.c.d ControlMaster auto ControlPath ~/.ssh/sockets/%r@%h:%p

The goal is to only allow connections to the server in AES 256 Counter mode, with umac-64 or hmac-ripemd160 MACs, and compression, on a non-standard SSH port from a designated IP range using public key authentication. Connections will also be throttled and SSHGuard along with a few custom PF rules on the server will be used to block and log attackers. The commands that the client will use to connect to the server will look like this:client: 

$ alias sshconnect="ssh -l bryan a.b.c.d -p 21465 -C -c aes256-ctr -m,hmac-ripemd160 client: 
$ alias sshtunnel="ssh -v -ND 8090 bryan@a.b.c.d -p 21465 -C -c aes256-ctr -m,hmac-ripemd160 client:
$ alias sshmonitor="yes | pv | ssh -l bryan a.b.c.d -p 21465 -C -c aes256-ctr -m,hmac-ripemd160 \"cat > /dev/null\"" client: 
$ alias sshportforward="ssh -f bryan@a.b.c.d -p 21465 -C -c aes256-ctr -m,hmac-ripemd160 -L 15478:localhost:15479 -N" client: 
$ alias sshportforward2="ssh -f bryan@a.b.c.d -p 21465 -C -c aes256-ctr -m,hmac-ripemd160 -L 17293:localhost:17294 -N"

Alternatively, Ciphers, MACs, and compression can be specified in the user config file as follows:

ServerAliveInterval 60 
    ControlMaster auto 
    ControlPath ~/.ssh/sockets/%r@%h:%p 
    Port 21465 
    User bryan 
    Ciphers aes256-ctr 
    Compression yes 
    StrictHostKeyChecking yes

User and Host certificates provide a more convenient method of authentication for multiple clients (users) and servers (hosts). Certificate revocation can also provide an easier method of quickly invalidating user access.A certificate authority key pair is first generated as follows. The ca is then placed in the /etc/ssh directory on the host.

ca $ ssh-keygen -t ecdsa -b 521 -f user_ca server $ sudo mv user_ca* /etc/ssh/

On the client, generate a public/private key pair and then copy the public key to the server so that it can be signed with the ca. Make sure to set the validity period of the certificate. Alternatively, a host key may be signed with a ca key that is stored in a PKCS11 token. OpenSSH supports ca keys stored PCKS11 tokens. Check the version of SSH and see ssh-keygen for more information.client 

client $ ssh-keygen -t ends -b 521 -f ~/.ssh/id_ecdsa 
client $ scp .ssh/ bryan@server-ca:~/user_public_keys 
server-ca $ ssh-keygen -s /etc/ssh/user_ca \ 
      -O source-address=clientip 
      -O permit-pty 
      -O no-port-forwarding       
      -O no-user-rc 
      -O no-x11-forwarding \ -V -1d:+52w1d -z 6739301351 -I "bryan"       -n bryan,clienthostname
id "bryan" serial 6739301351 for bryan,clienthostname valid from 2011-08-18T15:05:24 to 2012-08-17T15:05:24 

Copy the signed user cert back to the client.

client $ scp bryan@server:~/user_public_keys/ ~/.ssh/ 

Setup TrustedUserCAKeys and AuthorizedPrincipalsFile files. Subsequently, set appropriate options in /etc/ssh/sshd_config on the server.

server-ca $ sudo cat /etc/ssh/ > /etc/ssh/trusted_user_ca_keys 

Modify /etc/ssh/authorized_principals to include the following lines.bryan from="clientip" bryan
Modify /etc/ssh/sshd_config on the server to include the following lines

TrustedUserCAKeys /etc/ssh/trusted_user_ca_keys 
AuthorizedPrincipalsFile /etc/ssh/authorized_principals 

Now, restart sshd on the server and add an appropriate host configuration for certificate authentication to ~/.ssh/config on the client.

Last of all, setup a host certification via the -h option with ssh-keygen when signing a host key.

It is important to always keep OpenSSH updated with the latest, stable version that has been released for the operating system.

Thursday, March 3, 2011

Device Encryption in Android 3.0

Transparent encryption of block devices in Android 3.0

The Motorola Xoom and a number of new tablets on the market run Android 3.0, Honeycomb.  Android 3.0 is built on the 2.6.36 Linux kernel.  Most, if not all, of the Android tablets that are coming to market feature an Invidia Tegra 2 processor.  The 2.6.36 Linux kernel on these Android 3.0 Tegra 2 tablets introduces transparent, whole disk encryption to the everyday user.  Transparent, whole disk encryption is provided by the dm-crypt device-mapper target in the Linux kernel.  This target provides a virtual layer on top of an existing block device and uses the crypto APIs in the Linux kernel for encryption and decryption of the underlying block devices.

Whether commands are being typed via a shell over a serial port or an e-mail application is being used to check e-mail, reads and writes to the file system are performed in the same manner with no changes to the upper level applications.

After pressing the power button on the back of the Xoom tablet, the tablet boots and the user is presented with the desktop environment; from which he or she may choose to play a game, check e-mail, or read an e-book.By tapping on settings and then Location & security, one can choose to "Encrypt tablet" from this screen.  Upon doing so, the encryption process takes about 1.0 hours and the user is presented with a few basic screens.

After the encryption process is finished, the tablet is powered down. Upon rebooting the tablet, the user is prompted to input a pin code which is used to unlock the device.  Upon typing the correct pin code, the tablet powers up as normal and the user can proceed with performing his or her standard activities - checking e-mail, reading e-books, etc.

The Linux 2.6.36 kernel supports what is called the device mapper framework. The Device Mapper Framework allows the mapping of virtual layers on top of block devices for doing things like striping and mirroring.  device-mapper also provides a convenient target called dm-crypt.  dm-crypt is a device-mapper crypto target.  the dm-crypt target provides transparent encryption of block devices.

Before the encryption operation above, here is the output of the mount command which shows the device name and mount point.  This is an important partition because it is where the user's data is stored.  Consequently, this is the partition that will get encrypted.

/dev/block/platform/sdhci-tegra.3/by-name/userdata on /data type ext4 (rw,nosuid,nodev,noatime,barrier=1,data=ordered)

A few mount options to take note of:  noatime, barriers and data=ordered

...And after the encryption operation

/dev/block/dm-0 /data ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered 0 0

dmsetup will give us more information. Per the below command,  dm-crypto device mapper target called crypt, has been setup in the kernel.  The dm-crypt target provides transparent encryption and decryption of data on the block device using the crypto APIs in the Linux kernel.

# dmsetup targets

crypt            v1.7.0
striped          v1.3.0
linear           v1.1.0
error            v1.0.1
# dmsetup status

datadev: 0 61326304 crypt

Albeit the details surrounding key storage (see kernel source), supported ciphers (cat /proc/crypto), and hardware acceleration (see kernel source), here are some rudimentary performance tests that were run before and after encrypting /data.  For the interested reader, there are some kernel level details related to the Tegra 2 processor which one can discover by going through the source code for the Linux 2.6.36 Tegra 2 branch.

The initial results of the the basic tests look good. There is a dedicated kernel thread for handling IO.  The read latency appears to be related to the kernel IO thread since reads on flash based storage devices can usually be performed in near constant time.


Unencrypted (2 GB Write - 104857 2k blocks)

/data/local/tmp # time dd if=/dev/zero of=ofile bs=2k count=1048572

1048572+0 records in
1048572+0 records out
2147475456 bytes (2.0GB) copied, 255.912521 seconds, 8.0MB/s
real    4m 17.25s
user    0m 0.73s
sys     0m 24.55s

Unencrypted (2 GB Read - 104857 2k blocks)

/data/local/tmp # time dd of=/dev/null if=ofile bs=2k count=1048572

1048572+0 records in
1048572+0 records out
2147475456 bytes (2.0GB) copied, 101.749864 seconds, 20.1MB/s
real    1m 41.79s
user    0m 1.15s
sys     0m 17.62s

Encrypted (2 GB Write - 104857 2k blocks)

/data/local/tmp # time dd if=/dev/zero of=ofile bs=2k count=1048572

1048572+0 records in
1048572+0 records out
2147475456 bytes (2.0GB) copied, 260.219584 seconds, 7.9MB/s
real    4m 26.94s
user    0m 0.64s
sys     0m 24.12s

Encrypted (2 GB Read - 104857 2k blocks)

/data/local/tmp # time dd of=/dev/null if=ofile bs=2k count=1048572

1048572+0 records in
1048572+0 records out
2147475456 bytes (2.0GB) copied, 124.291204 seconds, 16.5MB/s
real    2m 4.31s
user    0m 0.47s
sys     0m 7.74s


As a side note:  After performing the encryption operation, and subsequently building a Tegra 2 kernel for experimentation, f fastboot boot myKernelBootImg was run from the bootloader, after which a prompt indicated an error message which stated that the "fastboot boot" command is not allowed on consumer devices

In conclusion, the devicer-mapper target, dm-crypt, provides transparent, whole-disk encryption for Android 3.0 based tablet devices.  It is something worthy of heavy consideration.

* get the block size for a device blockdev --getbsz /dev/block/dm-0