I don't quite understand one-way md5 password decryption.
What provides uniqueness of an md5 hash for a given database? Is a hashing algoritm(key) specific for a hosting server or for a database itself?
After all, there must be somewhere a unique encryption/decryption key, isn't it? If so, where is it found, and how come a hacker who gains access to (say) hashed user passwords list, cannot access the key as well?