cannot install opencv with homebrew(MD5 not supported)

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Hi, I am working on an iris recognition project following this URL:http://www.nist.gov/itl/iad/ig/upload/NIST_VASIR_Beta2-2_userguide-2.pdf

Here is the instruction in it about how to install openCV 2.3.1:

For Mac

The following steps exemplify the installation of OpenCV 2.3.1 on Mac OS X 10.8.4:

1) Install Homebrew (http:/brew.sh) by running in a Terminal/shell (w/o the leading “$”): $ ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/...

2) Edit your “~/.profile” and add: export PYTHONPATH="/usr/local/lib/python2.7/site-packages:$PYTHONPATH"

3) Add the science “tap”: $ brew tap homebrew/science

4) Refresh Homebrew’s package information: $ brew update

5) Go back to OpenCV version 2.3.1: $ cd /usr/local/Library/Taps/homebrew-science/opencv.rb $ git checkout cdaf83d opencv.rb

6) Install OpenCV 2.3.1: $ brew install --32-bit --with-libtiff opencv

I followed the instruction with basically no problem(although some minor differences as this instruction was written 1 or 2 years ago) until step 6 which requires me to install OpenCV 2.3.1 with this command: $ brew install --32-bit --with-libtiff opencv

However I got this error: Error: MD5 support has been dropped for security reasons. Please switch this formula to SHA256.

I also tried the following command: $ brew install opencv which returned me the some error.

FYI: My operation system is Mac OS 10.9.5

Could someone help? Thanks in advance.