question: public String hashKeyForDisk ( String key ) { String cacheKey ; try { final MessageDigest mDigest = MessageDigest . getInstance ( "MD5" ) ; mDigest . update ( key . getBytes ( ) ) ; cacheKey = bytesToHexString ( mDigest . digest ( ) ) ; } catch ( NoSuchAlgorithmException e ) { cacheKey = String . valueOf ( key . hashCode ( ) ) ; } return cacheKey ; }
target:  Using the MD5 algorithm to encrypt the key of the incoming and return. 