I have a
.png file that is encrypted, but I know the first characters of the (decrypted) file are the highlighted/selected characters below (as they appear in notepad++). Can I decrypt the file if I don't know the key (but perhaps if I know the algorithm, mode, and/or key length). At worst, perhaps I could only try the key(s) that produce the first few characters and ignore the rest to decrypt it.
the specific encrypted file's first few characters: