Comparing Message Digest Output of MD5 and SHA

JDK Tutorials - Herong's Tutorial Examples

∟Message Digest Algorithm Implementations in JDK

∟Comparing Message Digest Output of MD5 and SHA

This section a tutorial example on how to view and compare message digest output from two standard message digest algorithms MD5 and SHA.

The message digest output file contains binary data, which cannot be viewed directly. In order to see the digest data, I need to use my other program, HexWriter.java, to convert binary data to hex numbers. See chapter "Encoding Conversion" for details.

Here is how to look at the digest data in hex numbers, 16 bytes per line:

herong> javac HexWriter.java

herong> java HexWriter digest.sha digest_sha.hex

herong> more digest_sha.hex
0520E172B3E334C9BDD92D7ADBC98F1C
BD4162D0

My second test is to see the digest data of the same input data, JcaMessageDigest.class, using MD5 algorithm:

herong> java JcaMessageDigest JcaMessageDigest.class digest.md5 MD5

MessageDigest Object Info:
Algorithm = MD5
Provider = SUN version 10
Digest Length = 16
toString = MD5 Message Digest from SUN, <initialized>

Message Digest Processing Info:
Number of input bytes = 2555
Number of output bytes = 16

herong> java HexWriter digest.md5 digest_md5.hex

herong> more digest_md5.hex
7DA3B53BBEC296D835DC58A1AD5FA664

My third test is to see how the digest data changes if I add one byte to the input data:

herong> copy con dot.tmp
.^Z

herong> copy JcaMessageDigest.class JcaMessageDigest_1.class

herong> more dot.tmp >> JcaMessageDigest_1.class

herong> dir *.class
   2,217 JcaMessageDigest.class
   2,218 JcaMessageDigest_1.class

herong> java JcaMessageDigest JcaMessageDigest_1.class digest_1.md5 MD5

MessageDigest Object Info:
Algorithm = MD5
Provider = SUN version 1.8
Digest Length = 16
toString = MD5 Message Digest from SUN, <initialized>

Message Digest Processing Info:
Number of input bytes = 2218
Number of output bytes = 16

herong> java HexWriter digest_1.md5 digest_1_md5.hex

herong> more digest_1_md5.hex
31B82738B990A2ECDA63547B660CA0F0

A couple of interesting notes here:

The first command is a special trick I learned from DOS system. It allows you to enter data into a file directly from keyboard without using any editor. In the command, "con" is used as a special file name to represent the console, keyboard and monitor. When entering data from keyboard, Control-Z must be used to simulate the end-of-file sign.
The second and third commands add the one-byte file, dot.tmp, to the end of the class file, JcaMessageDigest.class.
The forth command generates MD5 digest data from the modified class file. The new digest data is very different than old digest data.