Example #1
0
 /// <summary>  The constructor. </summary>
 /// <param name="s">The underlying stream</param>
 /// <param name="cipher">The pre-initialized ZipCrypto object.</param>
 public ZipCipherStream(System.IO.Stream s, ZipCrypto cipher)
 {
     if (s == null) throw new ArgumentNullException("s");
     _cipher = cipher;
     _s = s;
 }
Example #2
0
        public static ZipCrypto ForRead(string password, ZipEntry e)
        {
            System.IO.Stream s = e._archiveStream;
            e._WeakEncryptionHeader = new byte[12];
            byte[] eh = e._WeakEncryptionHeader;
            ZipCrypto z = new ZipCrypto();

            if (password == null)
                throw new BadPasswordException("This entry requires a password.");

            z.InitCipher(password);

            ZipEntry.ReadWeakEncryptionHeader(s, eh);

            // Decrypt the header.  This has a side effect of "further initializing the
            // encryption keys" in the traditional zip encryption.
            byte[] DecryptedHeader = z.DecryptMessage(eh, eh.Length);

            // CRC check
            // According to the pkzip spec, the final byte in the decrypted header
            // is the highest-order byte in the CRC. We check it here.
            if (DecryptedHeader[11] != (byte)((e._Crc32 >> 24) & 0xff))
            {
                // In the case that bit 3 of the general purpose bit flag is set to
                // indicate the presence of an 'Extended File Header' or a 'data
                // descriptor' (signature 0x08074b50), the last byte of the decrypted
                // header is sometimes compared with the high-order byte of the
                // lastmodified time, rather than the high-order byte of the CRC, to
                // verify the password.
                //
                // This is not documented in the PKWare Appnote.txt.  It was
                // discovered this by analysis of the Crypt.c source file in the
                // InfoZip library http://www.info-zip.org/pub/infozip/
                //
                // The reason for this is that the CRC for a file cannot be known
                // until the entire contents of the file have been streamed. This
                // means a tool would have to read the file content TWICE in its
                // entirety in order to perform PKZIP encryption - once to compute
                // the CRC, and again to actually encrypt.
                //
                // This is so important for performance that using the timeblob as
                // the verification should be the standard practice for DotNetZip
                // when using PKZIP encryption. This implies that bit 3 must be
                // set. The downside is that some tools still cannot cope with ZIP
                // files that use bit 3.  Therefore, DotNetZip DOES NOT force bit 3
                // when PKZIP encryption is in use, and instead, reads the stream
                // twice.
                //

                if ((e._BitField & 0x0008) != 0x0008)
                {
                    throw new BadPasswordException("The password did not match.");
                }
                else if (DecryptedHeader[11] != (byte)((e._TimeBlob >> 8) & 0xff))
                {
                    throw new BadPasswordException("The password did not match.");
                }

                // We have a good password.
            }
            else
            {
                // A-OK
            }
            return z;
        }