mcrypt package is not included in the default CentOS repositories. It can be installed from the Remi repository.
In order to install Redis, you need to have root permission.
STEP 1. Enabling the Remi repository
sudo yum install epel-release yum-utils sudo yum install http://rpms.remirepo.net/enterprise/remi-release-7.rpm sudo yum-config-manager --enable remi
STEP 2. Install the Redis package by typing:
sudo yum install redis
STEP 3. Install mcrypt
You can simply install mcrypt as following
sudo yum -y install mcrypt php-mcrypt