Develop Reference

How to check for an encrption for a 7z file?

I need to check a 7z file for encryption.
I am using sevenzipjbind and using the property ENCRYPTED, but it seems it involves a lot more steps after that which I am not able to certain.

You can use commons-compress which supports reading encrypted 7zip archives. From the official website:
The ar, arj, cpio, dump, tar, 7z and zip formats are supported as archivers where the zip implementation provides capabilities that go beyond the features found in java.util.zip. As of Commons Compress 1.18 support for the dump and arj formats is read-only - 7z can read most compressed and encrypted archives but only write unencrypted ones. LZMA(2) support in 7z requires XZ for Java as well.
Take a look at SevenZFile class to see if you can use it. Internally SevenZFile reads archive header to check the password.

Reading Password-Protected ZIP Files in Java

I have zipped and protected a file with a password.
Now I need to retrieve the file back with java. So I need to unlock the password and unzip with Java to make a proper connection to the file.
My first Questions is: Does Java unzip and unlock the zipped file on the local drive? (So no point protecting it?).
I have read all about encryption, but really searching for the easiest way here.
This link: http://blog.alutam.com/2009/10/31/reading-password-protected-zip-files-in-java/
My second Question is about the link above: I cannot find the lines where he is pointing to his zipped file on the local drive+ the password he uses to unlock the file (is it hardcoded?)
Thank you

You may want to have a look on Zip4j
Key features:
Create, Add, Extract, Update, Remove files from a Zip file
Read/Write password protected Zip files
Supports AES 128/256 Encryption
Supports Standard Zip Encryption
Supports Zip64 format
Supports Store (No Compression) and Deflate compression method
Create or extract files from Split Zip files (Ex: z01, z02,...zip)
Supports Unicode file names
Progress Monitor

Is it possible to open a TrueZIP archive from a stream?

Using TrueZIP, is there a way to open and modify an existing ZIP file from a stream (it may of course be outputted using another stream)?
I have code for modifying a ZIP that works perfectly as long as I work on an existing real ZIP file on the file system but I have a requirement that all temporary files need to be encrypted while stored on disk. In most part of our application this is easy to achieve (using CipherOutputStream and CipherInputStream) but I have one function that uses TrueZIP to update an existing ZIP file. This part obviously fails if the file is encrypted.
The ZIP files will be consumed by proprietary applications that do not support encryption so using the encryption that is part of the ZIP specification isn't possible.
The reason we are using TrueZIP is that we need the support for Zip64 (which I know is included in Java 7 but we cannot switch right now).

No, an archive file must be stored in accessible file system to use it with TrueZIP. But you have a number of other options:
TrueZIP uses instances of the IOPoolService interface to manage temporary files. You could provide your own implementation which encrypts all temporary files or maybe even just stores them on the heap (if they are small). Have a look at the TrueZIP Driver FILE to see the reference implementation.
You could use the ParanoidZipRaesDriver to use RAES encrypted ZIP files. This driver ensures that no unencrypted temporary files are used by limiting the number of concurrent threads for writing an archive file to one.
You could use the standard ZIP drivers with FsOutputOption.ENCRYPT to switch on WinZip AES encryption. To ensure that no unencrypted temporary files are used, you could then override the ZipDriver.newOutputSocket method just like the ParanoidZipRaesDriver does.

How to open password protected zip file using truezip library in java

Please show me sample of code how to open password protected file using truezip library.
If you don't have a link to sample code please show me method to open this file.

Have a look at the answers of this question: several suggestion are available. A quick google search make me thinks that TrueZip supports only its own encryption: read here

TrueZIP supports only its own encryption scheme: ZIP.RAES alias TZP
Any other ZIP encryption scheme, e.g. WinZIP encryption, is not available at this time.
If you want this feature supported, you can vote for it here: http://java.net/jira/browse/TRUEZIP-9

Encrypting zip files with a password based on Zip 2.0 encryption

I am trying to zip and encrypt files in Java (1.6) with a password based on the earlier Zip 2.0 encryption. I have used AES 256 bit encrytpion to encrypt zip files with password and have successfully been able to do so.
Though AES is a stronger and a more secure encryption standard, i need to find a standard that is more widely supported across all zip clients so that the users have a higher success rates opening the password protected zip files. So i was looking for some Zip 2.0 based encryption to encrypt my files. Any help would be appreciated!
Thanks!

You can try Zip4j, a pure java library to handle zip file. It supports encryption/decryption of PKWare and AES encryption methods.
http://www.lingala.net/zip4j/
Key features:
Create, Add, Extract, Update, Remove files from a Zip file
Read/Write password protected Zip files
Supports AES 128/256 Encryption
Supports Standard Zip Encryption
Supports Zip64 format
Supports Store (No Compression) and Deflate compression method
Create or extract files from Split Zip files (Ex: z01, z02,...zip)
Supports Unicode file names
Progress Monitor
License:
Zip4j is released under Apache License, Version 2.0

I think that nearly all zip-clients do support the WinZip-AES-encryption. As WinZip is far more spread than the original pkzip, it's encryption has become the de-facto standard.
Do you have a specific client which does not support the aes-encryption?