A: First, as a best practice you should not be encrypting your shell script. You should really document your shell script properly so that anybody who views it understands exactly what it does. If it contains sensitive information like password, you should figure out a different approach to write the shell script without having to encrypt it.
That being said, if you still insist on encrypting a shell script, you can use SHC utility as explained below. Please note that encrypted shell script created by shc is not readable by normal users. However someone who understands how this works can extract the original shell script from the encrypted binary created by shc.
SHC stands for shell script compiler.
1. Download shc and install itDownload shc and install it as shown below.
# wget http://www.datsi.fi.upm.es/~frosal/sources/shc-3.8.7.tgz # tar xvfz shc-3.8.7.tgz # cd shc-3.8.7 # makeVerify that shc is installed properly.
$ ./shc -v shc parse(-f): No source file specified shc Usage: shc [-e date] [-m addr] [-i iopt] [-x cmnd] [-l lopt]
2. Create a Sample Shell ScriptCreate a sample bash shell script that you like to encrypt using shc for testing purpose.
For testing purpose, let us create the following random.sh shell script which generates random numbers. You have to specify how many random numbers you like to generate.
$ vi random.sh #!/bin/bash echo -n "How many random numbers do you want to generate? " read max for (( start = 1; start <= $max; start++ )) do echo -e $RANDOM done $ ./random.sh How many random numbers do you want to generate? 3 24682 1678 491
3. Encrypt the Shell Script Using shcEncrypt the random.sh shell scripting using shc as shown below.
$ ./shc -f random.shThis will create the following two files:
$ ls -l random.sh* -rwxrw-r--. 1 ramesh ramesh 149 Mar 27 01:09 random.sh -rwx-wx--x. 1 ramesh ramesh 11752 Mar 27 01:12 random.sh.x -rw-rw-r--. 1 ramesh ramesh 10174 Mar 27 01:12 random.sh.x.c
- random.sh is the original unencrypted shell script
- random.sh.x is the encrypted shell script in binary format
- random.sh.x.c is the C source code of the random.sh file. This C source code is compiled to create the above encrypted random.sh.x file. The whole logic behind the shc is to convert the random.sh shell script to random.sh.x.c C program (and of course compile that to generate the random.sh.x executable)
$ file random.sh random.sh: Bourne-Again shell script text executable $ file random.sh.x random.sh.x: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 2.6.18,
stripped $ file random.sh.x.c random.sh.x.c: ASCII C program text
4. Execute the Encrypted Shell ScriptNow, let us execute the encrypted shell script to make sure it works as expected.
$ ./random.sh.x How many random numbers do you want to generate? 3 7489 10494 29627Please note that the binary itself is still dependent on the shell (the first line provided in the random.sh. i.e /bin/bash) to be available to execute the script.
5. Specifying Expiration Date for Your Shell ScriptUsing shc you can also specify an expiration date. i.e After this expiration date when somebody tries to execute the shell script, they'll get an error message.
Let us say that you don't want anybody to execute the random.sh.x after 31-Dec-2011 (I used last year date for testing purpose).
Create a new encrypted shell script using "shc -e" option to specify expiration date. The expiration date is specified in the dd/mm/yyyy format.
$ ./shc -e 31/12/2011 -f random.shIn this example, if someone tries to execute the random.sh.x, after 31-Dec-2011, they'll get a default expiration message as shown below.
$ ./random.sh.x ./random.sh.x: has expired! Please contact your providerIf you like to specify your own custom expiration message, use -m option (along with -e option as shown below).
$ ./shc -e 31/12/2011 -m "Contact [email protected] for new
version of this script" -f random.sh $ ./random.sh.x ./random.sh.x: has expired! Contact [email protected] for new version of this script
6. Create Redistributable Encrypted Shell ScriptsApart from -e, and -m (for expiration), you can also use the following options:
- -r will relax security to create a redistributable binary that executes on other systems that runs the same operating system as the one on which it was compiled.
- -T will allow the created binary files to be traceable using programs like strace, ltrace, etc.
- -v is for verbose
$ ./shc -v -r -T -f random.sh shc shll=bash shc [-i]=-c shc [-x]=exec '%s' "[email protected]" shc [-l]= shc opts= shc: cc random.sh.x.c -o random.sh.x shc: strip random.sh.x shc: chmod go-r random.sh.x $ ./random.sh.x How many random numbers do you want to generate? 3 28954 1410 15234Finally, it is worth repeating again: You should not be encrypting your shell script in the first place. But, if you decided to encrypt your shell script using shc, please remember that a smart person can still generate the original shell script from the encrypted binary that was created by shc.