What is the SPK file format?
.spk files are associated with Synology DiskStation Manager (DSM) for NAS devices. .spk files are installation packages for applications or software updates distributed through Synology's Package Center. They are typically installed via Package Center in DSM - either by browsing the catalog or uploading the .spk manually. Internally, .spk packages are saved as TAR archives - specifically POSIX ustar format - holding an INFO metadata file, a package.tgz payload (the application files compressed as a .tgz archive), lifecycle scripts, icons and a license file. DSM 7 packages also carry a digital signature that Package Center verifies before installation.
NAS (short for Network Attached Storage) is a type of data storage server connected to a network. The main purpose of NAS is serving files for users connected to a network, typically a home or small company network. NAS devices are designed to be simple to manage even by non-computer-savvy users. NAS solutions also offer robust security features such as ACLs or automated data backup tools.
Security & safety
RISK: MEDIUMAn .spk is an installable software package that runs lifecycle scripts on your NAS with elevated privileges, so a malicious .spk could compromise the device. Install only from the official Package Center or reputable communities (e.g. SynoCommunity); DSM 7 requires packages to be signed and, by default, warns or blocks unsigned third-party packages - don't disable that protection casually. Inspecting an .spk as a TAR on a PC is harmless; it's installing untrusted ones on the NAS that carries risk.
Format details
in a nutshell- SpyProof! encrypted key file - An old encryption tool used .spk for symmetric key data - the rare meaning the DB name reflects.
- ESPRiT / game & speech (SPK) data packs - Several games and speech engines use .spk as a packed-data/sound archive; unrelated to Synology.
Programs that open SPK files
Windows3 apps
7-Zip
Open-source Right-click the .spk > 7-Zip > Open archive to inspect it as a TAR, then open package.tgz inside to see the app files (inspection only - install via DSM). 
Synology DSM Package Center
Built-in On the NAS: Package Center > Manual Install > upload the .spk to actually install the app. 
macOS2 apps
The Unarchiver
Free Open the .spk to extract it as a TAR for inspection; unpack package.tgz inside to view app files. 
Apple Archive Utility
Built-in Double-click (or rename to .tar) to expand the .spk and inspect its contents. 
Linux1 app
GNU Tar
Open-source Run 'tar -xvf package.spk' to inspect contents, then 'tar -xzf package.tgz' for the app files. Install on the NAS via DSM, not here. Technical details
deep spec| Container format | POSIX (ustar) TAR archive - uncompressed outer wrapper |
| Internal payload | `package.tgz` - gzip-compressed TAR holding the application files |
| Encoding | Binary |
| Magic bytes | "ustar" at byte offset 257 (POSIX TAR magic in the first 512-byte header block; no signature at offset 0) |
| MIME type | application/x-tar; alternative: application/octet-stream |
| Metadata file | `INFO` - plain-text file declaring package name, version, target architecture and minimum DSM version required |
| Compression | Outer TAR is uncompressed; internal payload (`package.tgz`) uses gzip compression |
| Code signing | DSM 7 packages include a digital signature file verified by Package Center before installation (not encrypted) |
| Lifecycle scripts | `preinst`, `postinst`, `preuninst`, `postuninst` shell scripts may be bundled and are executed by DSM during install/uninstall cycles |
| Target platform | Synology DiskStation Manager (Linux-based NAS firmware); contents can be inspected on Windows, macOS or Linux with any TAR tool |
| Installation method | Uploaded via DSM Package Center (Manual Install) or downloaded automatically from Synology's Package Center catalog |
| Typical file size | 100 KB to several hundred MB, depending on the bundled application |
| Architecture targeting | `INFO` field specifies target CPU architecture (e.g., `x86_64`, `armv7`, `aarch64`) to match the NAS hardware model |
| Developer | Synology Inc. |
| Released | 2010s (Synology DiskStation Manager Package Center) |
| Latest version | SPK structure for DSM 7.x (signed packages) |
| Open standard | Yes · royalty-free |
| Specification | help.synology.com |
SPK conversions
Community Q&A
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