Zip Archives

Abbrevia can extract any file from a PKZIP(tm)-compatible archive. All five of the classic compression methods used by PKZIP are supported for extracting files. For adding files to a PKZIP-compatible archive, Abbrevia does not support the older compression methods (i.e., shrinking, reducing, and imploding). Because deflating is the most efficient and most frequently used form of compression, Abbrevia uses it for compressing files. Abbrevia also supports storing for files that cannot be compressed efficiently, such as graphics files (e.g. Jpeg) whose data is already compressed.

Encryption

Abbrevia supports PKZIP file encryption. It can decrypt files that were encrypted by PKZIP and it can also encrypt files as they are added to an archive. A file is encrypted after it is compressed, and is decrypted before it is expanded. The encrypted file is stored.

Each file is encrypted using a user-supplied password, which is not stored in the archive. Each file in an archive can have a different password.

When you extract an encrypted file, you must supply the same password that was used to encrypt it. An archive can contain any combination of encrypted files (each possibly having a distinct password) and files that are not encrypted.

Abbrevia allows passwords up to 255 characters long. Passwords should generally be long (more than 8 characters) with a mixture of upper and lower case characters and punctuation. This makes unauthorized access to the encrypted file more difficult. While password protecting a ZIP file makes unauthorized access to the file more difficult, PKZIP's encryption support has significant weaknesses.

Self-Extracting Archives

A self-extracting archive is an executable file that, when executed, can extract files contained within itself. Abbrevia can operate on a self-extracting archive created by PKZIP. In addition, Abbrevia allows you to create self-extracting archive. Learn more about Abbrevia's support self-extracting archives here.

Spanning

In addition to self-extracting archives, Abbrevia also supports PKZIP-compatible spanned archives (also known as removable disk archives). Spanned archives are a great way to save large files (or set of files) to multiple floppy disk images.

When Abbrevia creates a spanned archive set or extracts files from a spanned set, it prompts the user to insert the appropriate disks (or specify the appropriate archive image file name). You can customize the prompts using the OnRequestBlankDisk, OnRequestImage, OnRequestLastDisk and OnRequestNthDisk events.

Abbrevia supports spanning on both the Windows and Linux operating systems.

Stream Compression

Abbrevia supports two type of stream compression and decompression. First, with Abbrevia you can create a ZIP item in an archive directly from a stream and extract an item from a ZIP archive directly to a stream. Adding an item directly from a stream involves storing the same type of PKZIP compatible header information into the archive.

The second type of stream compression/decompression simply takes an uncompressed stream and compresses its contents to a compressed stream. In this case, no PKZIP compatible header information is involved. Likewise, a compressed stream can be similarly decompressed.