Only the private key can decipher the encrypted message. And then there are one-way hash systems, such as SHA and MD5, which most operating systems use to store passwords. I discuss password management in detail later in the article. Some encryption implementations use all three methods to serve various different purposes in the system. This way, the system itself is protected in many ways, with each cryptography technique being put to its best use.
Most operating systems handle passwords by using one-way hashes.
What this means, in practice, is that your password is not stored anywhere on your computer. When you initially enter your password, the system encrypts it using a hash function. The system knows how it hashed the sequence of characters that is your password, so every time you log on, the system encrypts what you have just typed using the same hash function, and compares the encrypted results to the encrypted password. It compares, notes that the two hashes are the same, and lets you into your account. This is why it's important to protect your password file even though it's encrypted.