HashPump is a C++ based command line tool to exploit the Hash Length Extension Attack with various hash types supported, including MD4, MD5, SHA1, SHA256, and SHA512.
There’s a good write-up of how to use this in practical terms here: Plaid CTF 2014: mtpox
$ hashpump -h
HashPump [-h help] [-t test] [-s signature] [-d data] [-a additional] [-k keylength]
HashPump generates strings to exploit signatures vulnerable to the Hash Length Extension Attack.
-h --help Display this message.
-t --test Run tests to verify each algorithm is operating properly.
-s --signature The signature from known message.
-d --data The data from the known message.
-a --additional The information you would like to add to the known message.
-k --keylength The length in bytes of the key being used to sign the original message with.
Version 1.2.0 with CRC32, MD5, SHA1, SHA256 and SHA512 support.
<Developed by bwall(@botnet_hunter)>
You can download HashPump here:
$ git clone https://github.com/bwall/HashPump.git
$ apt-get install g++ libssl-dev
$ cd HashPump
$ make install
Or read more here.