DES Calculator

The DES Calculator applet is used to encrypt or decrypt test data values using DES block cipher. It takes a 64-bit (16 hex digit) data value and a 128-bit (32 hex digit) key. It can optionally provide a trace of the calculations performed, with varying degrees of detail.

Using the DES Calculator

The DEScalc.html page is used to access the DES Calculator. To use the calculator fill in the Input Data value (being 16 hexadecimal digits), and the DES Key (being 32 hexadecimal digits), and press either the Encrypt or Decrypt button, as required. The resulting value will be displayed, along with the trace of the calculation, at the level of detail specified by te Trace Level radio buttons. If there is an error in the supplied values, an error message will be displayed in red.

An example DES test value, taken from "H. Katzan, The Standard Data Encryption Algorithm, pp75-94, Petrocelli Books Inc., New York, 1977" is:

Key:        5B5A57676A56676E
Plaintext:  675A69675E5A6B5A
Ciphertext: 974AFFBF86022D1F

Encrypting the plaintext with the key should give the ciphertext, decrypting the ciphertext with the key should give the plaintext.

The Trace produced looks like (at level 2):

setKey(5b5a57676a56676e)

encryptDES(675a69675e5a6b5a)
  IP:	L0=ffb2194d, R0=004df6fb
  Rnd1	f(R0=004df6fb, SK1=38 09 1b 26 2f 3a 27 0f ) = 746fc91a
  Rnd2	f(R1=8bddd057, SK2=28 09 19 32 1d 32 1f 2f ) = 7add38ae
  Rnd3	f(R2=7a90ce55, SK3=39 05 29 32 3f 2b 27 0b ) = a5e3f499
  Rnd4	f(R3=2e3e24ce, SK4=29 2f 0d 10 19 2f 1d 3f ) = c5403e1c
  Rnd5	f(R4=bfd0f049, SK5=03 25 1d 13 1f 3b 37 2a ) = 91a62c82
  Rnd6	f(R5=bf98084c, SK6=1b 35 05 19 3b 0d 35 3b ) = 6aeb6bc3
  Rnd7	f(R6=d53b9b8a, SK7=03 3c 07 09 13 3f 39 3e ) = 1e9f7513
  Rnd8	f(R7=a1077d5f, SK8=06 34 26 1b 3f 1d 37 38 ) = 59d1851c
  Rnd9	f(R8=8cea1e96, SK9=07 34 2a 09 37 3f 38 3c ) = 0fc4b474
  Rnd10	f(R9=aec3c92b, SK10=06 33 26 0c 3e 15 3f 38 ) = 8de55e67
  Rnd11	f(R10=010f40f1, SK11=06 02 33 0d 26 1f 28 3f ) = dced7991
  Rnd12	f(R11=722eb0ba, SK12=14 16 30 2c 3d 37 3a 34 ) = 898d0def
  Rnd13	f(R12=88824d1e, SK13=30 0a 36 24 2e 12 2f 3f ) = 34cee3c3
  Rnd14	f(R13=46e05379, SK14=34 0a 38 27 2d 3f 2a 17 ) = 6a4754b1
  Rnd15	f(R14=e2c519af, SK15=38 1b 18 22 1d 32 1f 37 ) = 5bac9dc6
  Rnd16	f(R15=1d4ccebf, SK16=38 0b 08 2e 3d 2f 0e 17 ) = e448c462
  FP:	L=974affbf, R=86022d1f
 returns 974affbf86022d1f

974affbf86022d1f

The provides details of:

the 64-bit (16 hex digit) key used (should be same as specified)
the 64-bit (16 hex digit) data value used (should be same as specified), and whether encrypt or decrypt has been requested
the left and right data halves after the initial permutation
for each of the 16 rounds, the 32-bit right half data value, the 48-bit (as 8 x 6-bit values) subkey, and the output of the non-linear function f which will be XOR'd with the left half data value (which was the right half in the previous round)
and the final value computed (being the en/decrypted original data value), after the final permutation, which should be as shown as the result.

Installing the DES Calculator on your own System

You can install the DES Calculator on your own system by uploading the following files, and saving them all in the same directory:

DEScalc.html: the HTML file used to run the applet
DEScalc.jar: the Java JAR file containing the code for the program, which is loaded by DEScalc.html.

Then open your local saved copy of DEScalc.html in your favorite (Java enabled) web browser. You may need to install a suitable Java v1.4 plugin for your browser - this is available from the J2SE Java distributions, which are included in the useful programs area for this course (CD only). You will need to copy/link the appropriate browser plugin file from the J2SE installation area to the plugin directory for your browser and restart it.

If you want to look under the hood, the sources are available in the jarfile. Copy it onto your system, extract files with "jar xvf DEScalc.jar", and look at the README file for more information. A Unix Makefile for building the sources using the Java SDK is included. The source code is written for clarity, ease of relation to the algorithm description, and ease of tracing intermediate values, not for efficiency! It is designed to be used to help students in my cryptography course better understand the operation of this cipher, as for example by doing my DES lab.

Authorship & Copyright

The DES Calculator applet was written by Lawrie Brown from ADFA, Canberra Australia. Lawrie's code is Copyright © 2005 by Lawrie Brown. Permission to reuse this code as desired is granted, provided due acknowledgement is given of the author and source of the original code.

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Lawrie.Brown@adfa.edu.au / 7 Jun 2005