Both the repository and Solr have their own public/private key pair, signed by an Alfresco Certificate Authority, which are stored in their own respective keystores. These keystores are bundled with Alfresco. You can also create your own keystores. For an overview on how to create an SSL public/private key and certificate for the repository, see Generating Repository SSL Keystores.
Keystores are used also to protect repository and Solr communications using encryption and mutual authentication. To do this, keystores store RSA keys and certificates.
It is assumed that the keystore files are stored in alf_data. Place the keystore files from the directory repository/config/alfresco/keystore in the $ALF_DATA/keystore directory.