Author Topic: Support for PKZip AES-256 Strong Decryption Format  (Read 5937 times)

shazin

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Support for PKZip AES-256 Strong Decryption Format
« on: January 16, 2013, 11:24:06 AM »
Currently Zip4J Supports Winzip AES-256 bit Decryption by checking the Compression method to be 99.
But a growing requirement is there for PKZip AES-256 bit Strong Decryption.

Winzip AES-256 Cryptographic Header will only have 16 bytes of Salt value + 2 bytes of Password Verification bytes.

But PKZIP AES-256 Cryptographic Header will have the following fields in it.

Decryption header record preceding compressed file data.

                 -Decryption Header:

                  Value     Size     Description
                  -----     ----     -----------
                  IVSize    2 bytes  Size of initialization vector (IV)
                  IVData    IVSize   Initialization vector for this file
                  Size      4 bytes  Size of remaining decryption header data
                  Format    2 bytes  Format definition for this record
                  AlgID     2 bytes  Encryption algorithm identifier
                  Bitlen    2 bytes  Bit length of encryption key
                  Flags     2 bytes  Processing flags
                  ErdSize   2 bytes  Size of Encrypted Random Data
                  ErdData   ErdSize  Encrypted Random Data
                  Reserved1 4 bytes  Reserved certificate processing data
                  Reserved2 (var)    Reserved for certificate processing data
                  VSize     2 bytes  Size of password validation data
                  VData     VSize-4  Password validation data
                  VCRC32    4 bytes  Standard ZIP CRC32 of password validation data

And requires the following algorithm to be applied in reverse to Decrypt.

Password = GetUserPassword()
            MasterSessionKey = DeriveKey(SHA1(Password))
            RD = CryptographicStrengthRandomData()
            For Each File
               IV = CryptographicStrengthRandomData()
               VData = CryptographicStrengthRandomData()
               VCRC32 = CRC32(VData)
               FileSessionKey = DeriveKey(SHA1(IV + RD)
               ErdData = Encrypt(RD,MasterSessionKey,IV)
               Encrypt(VData + VCRC32 + FileData, FileSessionKey,IV)
            Done

Please provide support for this type of Password protected AES-256 bit encryptions also.

Source : http://www.pkware.com/documents/casestudies/APPNOTE.TXT

Kadindii

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Re: Support for PKZip AES-256 Strong Decryption Format
« Reply #1 on: February 03, 2015, 06:48:41 AM »
I want to see more like this for a long time.

boxseriez

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Re: Support for PKZip AES-256 Strong Decryption Format
« Reply #2 on: February 03, 2015, 10:03:51 AM »
Your making me think. What to do about it, you have to say on the topic.

 


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