This is a small java application that demonstrates a successfull Padding Oracle attack.
The rough idea is that a text encrypted with a block cipher (e.g. AES, 3DES, etc) in CBC mode of operation and PKCS7 padding may be decrypted without knowledge of the secret key. The only thing that is necessary is the so called Padding oracle. A padding oracle leaks data about whether the padding of an encrypted message is correct or not. Just that.
The application encrypts a text message and tries to decrypt it. The bundle contains a padding oracle.
More details about padding oracle attacks are available here. There was missing information about some implementation cornercases - please see here.
On a Windows machine, for exmple:
mkdir po
cd po
git clone https://github.com/luchob/padding-oracle.git .
Type gralew run. You should see output similar to the following:
gradlew run
:compileJava
:processResources UP-TO-DATE
:classes
:run
15:39:06.823 [main] DEBUG eu.balev.poracle.Main - Going to try to encrypt a given text with AES/CBC/PKCS5Padding and decrypt it withouth knowledge of the key with a padding oracle attack.
15:39:07.273 [main] DEBUG eu.balev.poracle.Main - Length of the text to encrypt is 78 bytes.
15:39:07.273 [main] DEBUG eu.balev.poracle.Main - Length of the encrypted text is 80. Spread over 5 blocks of 16 bytes.
15:39:07.723 [main] DEBUG eu.balev.poracle.Main - Original text is: Hi, I'm Lucho! This is a test plain text, encrypted with AES/CBC/PKCS5Padding.
15:39:07.723 [main] DEBUG eu.balev.poracle.Main - Decrypted text is: Hi, I'm Lucho! This is a test plain text, encrypted with AES/CBC/PKCS5Padding.
BUILD SUCCESSFUL
Total time: 5.903 secs
The application can be easily explored and experimented with in the Eclipse IDE. The application comes with a gradle wrapper and eclipse plugin. The eclipse plugin is able to generate Eclipse project files. To genreate Eclipse project files run:
gradlew eclipse
After that import the application as an existing Eclipse project. There is single class Main which is an entry point to the app. If another IDE is used please import the java sources as appropriate for it.
The performance of the application could have been better by:
- paralelizing the decryption operations
- improving the ambiguity resolution whenever there are padding byte conflicts
Please note that this is just an educational application and not all of the best coding practices are taken into account during development. The focus is on the padding oracle.
Bug reports and comments are welcome!