title: How do people go about attacking an encrypted file?
body: <p>I've been reading up on file encryption lately, and In many places I've seen warnings that encrypted files are susceptible to decryption by people so inclined regardless of encryption algorithm strength.</p>
  
  <p>However, I can't get my head around how someone would go about attempting to decrypt an encrypted file.</p>
  
  <p>For example, lets say you've got an encrypted file and you'd like to know it's contents. You have no idea what the key used to encrypt the file is, nor the encryption algorithm used. What do you do? (Assume for this example that the encryption algorithm is a symmetric-key algorithm such as AES-256, I.E. a file encrypted with key which requires said key to decrypt it).</p>
  
  <p>Additionally, how would your approach change if you knew the encryption algorithm used? (Assume in this case that the encryption algorithm used is AES-256, with a random key + salt).</p>