cpackget: Open-CMSIS-Pack Package Installer

This utility allows embedded developers to install (or uninstall) Open-CMSIS-Pack software packs to their local environments. It is one of the Open-CMSIS-Pack's devtools.

How to get cpackget

Please visit the latest stable release page and download the binary for your system, decompress it and run the binary named cpackget in the folder. It's also distributed as a part of the Open-CMSIS-Pack's toolbox.

Usage

cpackget installs packs via a CLI interface and it's intended to be easy to understand it. Here is how the command line looks like:

Usage:
  cpackget [command] [flags]

Available Commands:
  add              Add Open-CMSIS-Pack packages
  checksum-create  Generates a .checksum file containing the digests of a pack
  checksum-verify  Verifies the integrity of a pack using its .checksum file
  help             Help about any command
  init             Initializes a pack root folder
  list             List installed packs
  rm               Remove Open-CMSIS-Pack packages
  signature-create Digitally signs a pack with a X.509 certificate or PGP key
  signature-verify Verifies a signed pack
  update-index     Update the public index

Flags:
  -C, --concurrent-downloads uint   Number of concurrent batch downloads. Set to 0 to disable concurrency (default 5)
  -h, --help                        help for cpackget
  -R, --pack-root string            Specifies pack root folder. Defaults to CMSIS_PACK_ROOT environment variable
  -q, --quiet                       Run cpackget silently, printing only error messages
  -T, --timeout uint                Set maximum duration (in seconds) of a download. Disabled by default
  -v, --verbose                     Sets verboseness level: None (Errors + Info + Warnings), -v (all + Debugging). Specify "-q" for no messages
  -V, --version                     Prints the version number of cpackget and exit

Use "cpackget [command] --help" for more information about a command.

For example, if one wanted help removing a pack, running cpackget rm --help would print out useful information on the subject.

Specifying the working pack root folder

If cpackget is going to work on an existing pack root folder, there are two ways to specify it:

1. export CMSIS_PACK_ROOT=path/to/pack-root; cpackget add ARM.CMSIS
2. cpackget --pack-root path/to/pack-root pack add ARM.CMSIS

To create a new pack root folder with an up-to-date index file of publicly available Open-CMSIS-Pack packs run:

$ cpackget init --pack-root path/to/new/pack-root https://www.keil.com/pack/index.pidx

The command will create a folder called path/to/new/pack-root and the following subfolders: .Download, .Local, .Web. A copy of the index file (if specified) is placed in .Web/index.pidx.

If later it is needed to update the public index file, just run cpackget index https://vendor.com/index.pidx and .Web/index.pidx will be updated accordingly.

As of v0.7.0, the pack root is read-only, with permissions being handled by cpackget. Changing any permissions manually inside the pack root might cause erratic behavior, potentially breaking functionality.

Using the default pack root folder

If not specified as described in the previous section, cpackget will determine the pack root folder based on the Operating System and user environment.

This "default mode" enables a fast bootstrapping process, as cpackget will detect the presence of the public index file .Web/index.pidx in the default pack root and if it's missing, automatically populates/initializes it using the current index reference. This is the equivalent of running cpackget init https://www.keil.com/pack/index.pidx.

Adding packs

The commands below demonstrate how to add packs:

Install a pack version that is present in the file system already:

• cpackget add path/to/Vendor.PackName.x.y.z.pack

Install a pack version that can be downloaded using a web link:

• cpackget add https://vendor.com/example/Vendor.PackName.x.y.z.pack

Install a pack version from the public package index. The download url will be looked up by the tool:

• cpackget add Vendor.PackName.x.y.z or cpackget pack add Vendor::PackName@x.y.z

Install the latest published version of a public package listed in the package index:

• cpackget add Vendor.PackName or cpackget pack add Vendor::PackName

Install packs using version modifiers:

• cpackget add Vendor::PackName>=x.y.z, check if there is any version greater than or equal to x.y.z, install latest otherwise
• cpackget add Vendor::PackName@~x.y.z, check if there is any version greater than or equal to x.y.z

Install the pack versions specified in the ascii file. Each line specifies a single pack.

• cpackget add -f list-of-packs.txt

The command below is an example how to add packs via PDSC files:

• cpackget add path/to/Vendor.PackName.pdsc

Note that for adding packs via PDSC files is not possible to provide an URL as input. Only local files are allowed.

Listing installed packs

One could get a list of all installed packs by running the list command:

• cpackget list

This will include all packs that got installed via cpackget add command, including packs that were added via PDSC file.

There are also a couple of flags that allow listing extra information.

List all cached packs, that are present in the ".Download/" folder:

• cpackget list --cached

List all packs present in index.pidx:

• cpackget list --public

Accepting the End User License Agreement (EULA) from the command line

Some packs come with licenses and by default cpackget will prompt the user for agreement. This can be avoided by using the --agree-embedded-license flag:

• cpackget add --agree-embedded-license Vendor.PackName

Also there are cases where users might want to only extract the pack's license and not install it:

• cpackget add --extract-embedded-license Vendor.PackName

The extracted license file will be placed next to the pack's. For example if Vendor.PackName.x.y.z had a license file named LICENSE.txt, cpackget would extract it to .Download/Vendor.PackName.x.y.z.LICENSE.txt.

Removing packs

The commands below demonstrate how to remove packs.

Remove pack Vendor.PackName version x.y.z only, leave others untouched

• cpackget rm Vendor.PackName.x.y.z or cpackget rm Vendor::PackName@x.y.z

Remove all versions of pack Vendor.PackName

• cpackget rm Vendor.PackName or cpackget rm Vendor::PackName

Same as above, except that now it also removes the cached pack file.

• cpackget rm --purge Vendor.PackName: using --purge triggers removal of any downloaded files.

And for removing packs that were installed via PDSC files, consider the example commands below:

Remove a local pack, or remove all instances of a local pack that were added via different PDSC file locations

• cpackget rm Vendor.PackName.pdsc

Remove a specific PDSC of a pack

• cpackget rm path/to/Vendor.PackName.pdsc (cpackget list displays the absolute path of PDSC installed packs)

Updating the index

It is common that the index.pidx file gets outdated sometime after the pack installation is initialized. A good practice is to keep it always updated. One can do that by running

• cpackget update-index

This will use the address from the <url> tag inside index.pidx to retrieve a new version of the file. cpackget will also go through all PDSC files within .Web/ checking if the latest version has been oudated by the one matching the pack tag in index.pidx.

If wanted, the behavior above can be disabled by using --sparse flag, thus updating only the index.pidx.

Working behind a proxy

Some use cases might require network access via a proxy. This can be done via environment variables that are used by cpackget:

# Windows
% set HTTP_PROXY=http://my-proxy         # proxy used for HTTP requests
% set HTTPS_PROXY=https://my-https-proxy # proxy used for HTTPS requests

# Unix
$ export HTTP_PROXY=http://my-proxy         # proxy used for HTTP requests
$ export HTTPS_PROXY=https://my-https-proxy # proxy used for HTTPS requests

Then all HTTP/HTTPS requests will be going through the specified proxy.

Specifying timeouts

It's possible to set timeouts on commands that perform HTTP downloads, like cpackget add.
By default there's no timeout. Use the -T/--timeout global flag to specify in seconds the maximum waiting period for an HTTP GET:

$ cpackget add Vendor::PackName --timeout 5 # Maximum timeout of 5 seconds

Note: This feature will be reworked as not to set a hard timeout but an "exponential backoff" based on a number of retries. Some connections might take a lot longer than others, so if an operation like installing a public pack fails, increase the timeout or do not use it at all.

Parallel downloads

By default commands that mass download, like update-index, use 5 parallel connections to speed up the process. Use the -C/--concurrent-downloads global flag to specify the maximum number of parallel HTTP connections that can be opened:

$ cpackget add Vendor::PackName --concurrent-downloads 7 # Maximum 7 parallel downloads

Setting it to 0 will disable any parallel downloads.

Note: Some hosts might have firewalls/attack mitigation software that might identify multiple fast connections being opened as an attack. If downloading from a certain domain keeps failing, disable both concurrent downloads (set it to 0) and maximum timeout (by not using the flag).

Security features

The following features are not fully deployed yet and under constant review/discussion. These might suddenly change from release to release, with potential breaking changes. Always check the release/changelog first.

Integrity checking

As of release v0.7.0, it's possible to create a .checksum file of a local .pack. This file resembles a common digest file, used to confirm that an obtained piece of information matches the source's content.
Instead of just including the digest of the entire .pack as one, it lists the digests of all the files.

The extension includes the pack's name in its canonical form and hash algorithm used, appended by ".checksum": Pack.Vendor.1.0.0.sha256.checksum. Currently only works for local packs.

To create it:

$ cpackget checksum-create Vendor.PackName.1.0.0.pack

To verify a .pack against it's checksum file:

$ cpackget checksum-verify Vendor.PackName.1.0.0.pack

(the .checksum path is assumed to be the same as the .pack, but it can be specified with the -p flag)

Signed Packs

Likewise, this capability can also be extended to check for authenticity and non-repudiation. With the usage of X.509 certificates and/or PGP signatures, it's possible to create a chain of trust where pack vendors can provide verifiable proof that mitigates malicious attacks (like man-in-the-middle) and assure cpackget users the legitimacy and authenticity of their published packs.

Specification

To achieve this, a protocol was developed which takes advantage of the .pack format - packs are always zip files which by definition contain a general comment field. cpackget generates a signature which gets embed in the pack through this comment field.

This signature includes a cryptographic signed message of the hashed pack, binding its contents to an entity.

Two different modes are available, which have different requirements to create the signature:

• full: a X.509 public key certificate representing the vendor/publisher and its private key
• pgp: an armored PGP private key

Note: there's a third, "cert-only" mode, which is recommended only for testing/debugging purposes, as it doesn't include the signed digest of the pack.

The signature features the following format: [cpackget version]:[chosen mode]:[x509 certificate or PGP signed digest]:[signed digest]. As expected, the last two elements vary depending on the used mode, and are base64 encoded. Modes are represented with an f or c character.

To verify a pack, cpackget does the reverse operation: calculates the signed digest of the pack with the included X.509 pub key or referenced PGP key and matches it against what's written in the signature.

Example usage: X.509

A X.509 public key certificate and its private key is required to use the X.509 signing mode. OpenSSL is the industry standard for this. If you're running Linux, chances are you already have it installed in your system.

After installation, create both the certificate and private key with:

$ openssl req -x509 -newkey rsa:3072 -keyout x509_private_rsa.pem -out x509_certificate.pem -nodes

The specified key must be RSA, as of current implementation. The most important field is CN (Common Name), which names the entity signing the pack. Currently, cpackget does not enforce any specific CA to be the Issuer, so if following these steps, this field would represent both the Issuer and Subject names. Like the entire feature, this is very much subject to change.

Now, create the signature by providing a pack:

$ cpackget signature-create Vendor.PackName.1.2.3.pack --private-key x509_private_rsa.pem --certificate x509_certificate.pem

Information about the certificate will be displayed, and some basic validations on its integrity will be performed. Skip these with --skip-info and --skip-validation, respectively.

A copy of the pack (with a .signed extension) should be embed with the X.509 signed digest and the rest of the signature. Any zip tool like zipinfo can be used to view this:

$ zipinfo -z Vendor.PackName.1.2.3.pack.signed
Archive:  Vendor.PackName.1.2.3.pack.signed
cpackget-v0.8.5:f:LS0tLS1CRUdJTiBQR1AgU0lHTkFUVVJFLS0tLS0KVmVyc2lvbjogR29wZW5QR1AgMi40LjEwCkNvbW1lbnQ6IGh0dHBzOi8vZ29wZW5wZ3Aub3JnCgp3c0R6QkFBQkNnQW5CUUpqWXdYVENaQ1hzckI2R0VKeGJSWWhCTk94N0srOWZ:sCCre...

To verify this pack as legitimate and authentic, cpackget needs X.509 public key certificate, and the signed pack:

$ cpackget signature-verify Vendor.PackName.1.2.3.pack.signed --pub-key x509_certificate.pem
I: Pack signature verification success - pack is authentic

Example usage: PGP

A PGP key pair is required to use the PGP signing mode. GnuPG is the tried & tested tool for this purpose.

After installation, create one with:

$ gpg --full-generate-key

The specified key must be either RSA or Curve25519. Take note of the email field, as it will be used to export it.
Then, proceed to export both the public and private key locally, so it can be used as input for cpackget:

$ gpg --output public.pgp --armor --export <your-email>
$ gpg --output private.pgp --armor --export-secret-key <your-email>

With both of the keys locally saved, create the signature by providing a pack:

$ cpackget signature-create Vendor.PackName.1.2.3.pack --pgp --private-key private.pgp

A copy of the pack (with a .signed extension) should be embed with the PGP signed digest and the rest of the signature. Any zip tool like zipinfo can be used to view this:

$ zipinfo -z Vendor.PackName.1.2.3.pack.signed
Archive:  Vendor.PackName.1.2.3.pack.signed
cpackget-v0.8.5:p:LS0tLS1CRUdJTiBQR1AgU0lHTkFUVVJFLS0tLS0KVmVyc2lvbjogR29wZW5QR1AgMi40LjEwCkNvbW1lbnQ6IGh0dHBzOi8vZ29wZW5wZ3Aub3JnCgp3c0R6QkFBQkNnQW5CUUpqWXdYVENaQ1hzckI2R0VKeGJSWWhCTk94N0srOWZ...

To verify this pack as legitimate and authentic, cpackget needs the public counterpart of the signee's key, and the signed pack:

$ cpackget signature-verify Vendor.PackName.1.2.3.pack.signed --pub-key public.pgp
I: Pack signature verification success - pack is authentic

For more info on the current implementation: cpackget help signature-create and cpackget help signature-verify.

Contributing to cpackget tool

Found a bug? Want a new feature? Or simply want to fix a typo somewhere? If so please refer to our contributing guide.