How secure is Winzip and Winrar encryption?
Both programs WinZip and WinRar use AES (Advanced Encryption Standard) for encryption, when implemented correctly and in conjunction with a long alphanumerical hard to guess passphrase, the AES cipher is impossible to crack in a reasonable amount of time, that means in your lifetime.
State sponsored agencies are also not able to crack a password protected Zip or Rar file if this has been encrypted with a hard to guess pass, the law of mathematics just like the law of physics, is equal for everyone.
Recovering a password protected .zip or .rar file
The only known method to recover a forgotten password from a password protected .zip or .rar file created using the latest WinZip and WinRar versions, is to use a brute force attack. In a brute force attack an automated software will use up all of the dictionary words and run all of them attempting to match the file password.
Knowing if special characters and numbers were used in the passphrase, as well as knowing the length of the password, is very helpful while setting up the program to launch a brute force attack against the encrypted .zip or .rar file.Cracking a .zip file protected with encryption can take minutes, months or a hundred years, depending on processing power and how hard to guess the password is.
Services to crack encrypted .zip files
CloudCracker: A cloud based service for cracking WPA/WPA2 keys, CloudCracker offers brute force dictionary attacks against password hashes, wireless network keys and password protected documents, you could do this yourself in your computer but this service gives you access to an online cluster speeding up the process.
PWCrack: This password cracking service covers .zip encrypted files and PKZip files. Normally they will test a dictionary attack and brute force passwords up to 7 characters long.Password Crackers Inc. also offers services to crack many more different kind of encrypted files.
ElComSoft distributed password recovery
Software to crack password protected .zip files
Advanced Archive Password Recovery: This commercial software from ElComSoft helps you crack .zip and .rar encrypted files. They claim cracking archives created with WinZip 8.0 and earlier is possible in under one hour by exploiting an implementation flaw. For.zip or .rar files encrypted using the AES algorithm a brute force attack will be launched.
Passware Kit Enterprise: This a professional solution and not targeted to end users. Password Kit Enterprise supports cracking of multiple different files, from encrypted .zip and .rar up to launching brute force attcks on fully encrypted disks using TrueCrypt. Passware Kit EnterPrice can use multiple core CPUs and nVidia GPUs to speed up the dictionary attacks.
LastBit: This company makes a full range of password recovery software to help you bring back forgotten passwords on ICQ, Skype, Firefox, PDF, PowerPoint, Zip and many more applications. Various Lastbit products support rainbow tables which considerably speeds up dictionary attacks.
Zip Password Tool: An easy to use password recovery tool that works launching dictionary attacks on encrypted ZIP compatible software. It supports AES file encryption cracking and you can customize the brute force attack with special characters and national symbols, there is also a password recovery progress bar.
Zip Password Tool cracking .zip password
Tips to help you recover passwords from encrypted files
The following information will be of great use when launching a brute force or dictionary attack against any kind of password protected file or disk.
Find all the other passwords you can from the PC, notes around the computer and things someone might have saved in their web browsers and the Windows password, many people use the same or similar passwords everywhere.
By collecting all of the user passwords you will be able to observe a password pattern, like how many characters are normally used to create a password, names of cities, pets or family members being used, capitalizing of the first letter, etc, you can then customize your cracking software and set it up to use the same password pattern that the user normally adopts.
WinZip does not hide the encrypted filenames, you should be able to list them, unless they packed an archive inside an archive, that might give you a clue about the contents and whether it is worth to try and crack it or not. Notice that WinRar however, has an option where the user can encrypt the filenames, although this is not active by default and a checkbox needs to be ticked.
Cracking Zip file encryption from versions earlier than WinZip9.0 is easy and there is no need for a brute force attack as there was an implementation flaw in the encryption. Since WinZip version 9 and above .zip files are protected using 128 or 256 bit AES and with a sufficiently complicated password finding it out will be impossible.
Dictionary attacks for a long password with characters outside of 0-9 and A-Z are very slow, when you plan a dictionary attack on an encrypted .zip or .rar file, limit the yourself to alphanumeric unless you are certain a special character was used to create the password.
Another approach is to scan the disk for all words and then try them in different upper and low case combinations against the encrypted file.
Conclusion about security of encrypted .zip and .rar files
The latest versions of WinZip and WinRar both use AES128 or 256 bit for encryption, this cipher is a security standard and safe from cracking as long as the password is sufficiently long and contains upper and lowercase letters, special characters and numbers.
The weakest link in .zip and .rar encrypted passwords is you, avoid reusing your passwords anywhere else and writing them down, with the exception maybe being a password manager you trust.
Make sure that you only encrypt .zip and .rar files with WinZip9.0 and above and Winrar3.0 and above as earlier versions have some vulnerability.
There are many companies out there promising to crack files encrypted with WinZip and WinRar, and they all rely on the same, either you using an old version of the file compression software, or you choosing a weak and easy to guess password, as long as you cover those two vulnerabilities, you are safe using WinZip or WinRar for encryption, my first choice would be WinRar since WinZip does not support file name encryption.