Signing and Verifying Containers

Singularity 3.0 introduces the abilities to create and manage PGP keys and use them to sign and verify containers. This provides a trusted method for Singularity users to share containers. It ensures a bit-for-bit reproduction of the original container as the author intended it.

Verifying containers from the Container Library

The verify command will allow you to verify that a container has been signed using a PGP key. To use this feature with images that you pull from the container library, you must first generate an access token to the Sylabs Cloud. If you don’t already have a valid access token, follow these steps:

  1. Go to :

  2. Click “Sign in to Sylabs” and follow the sign in steps.

  3. Click on your login id (same and updated button as the Sign in one).

  4. Select “Access Tokens” from the drop down menu.

  5. Click the “Manage my API tokens” button from the “Account Management” page.

  6. Click “Create”.

  7. Click “Copy token to Clipboard” from the “New API Token” page.

  8. Paste the token string into your ~/.singularity/sylabs-token file.

Now you can verify containers that you pull from the library, ensuring they are bit-for-bit reproductions of the original image.

$ singularity pull library://alpine

$ singularity verify alpine_latest.sif
Verifying image: alpine_latest.sif
Data integrity checked, authentic and signed by:
    Sylabs Admin <>, KeyID 51BE5020C508C7E9

In this example you can see that Sylabs Admin has signed the container.

Signing your own containers

Generating and managing PGP keys

To sign your own containers you first need to generate one or more keys.

If you attempt to sign a container before you have generated any keys, Singularity will guide you through the interactive process of creating a new key. Or you can use the newpair subcommand in the key command group like so:.

$ singularity key newpair
Enter your name (e.g., John Doe) : Dave Godlove
Enter your email address (e.g., :
Enter optional comment (e.g., development keys) : demo
Generating Entity and OpenPGP Key Pair... Done
Enter encryption passphrase :

The list subcommand will show you all of the keys you have created or saved locally.`

$ singularity key list
Public key listing (/home/david/.singularity/sypgp/pgp-public):

0) U: Dave Godlove (demo) <>
   C: 2018-10-08 15:25:30 -0400 EDT
   F: 135E426D67D8416DE1D6AC7FFED5BBA38EE0DC4A
   L: 4096

In the output above, the letters stand for the following:

  • U: User

  • C: Creation date and time

  • F: Fingerprint

  • L: Key length

After generating your key you can optionally push it to the Keystore using the fingerprint like so:

$ singularity key push 135E426D67D8416DE1D6AC7FFED5BBA38EE0DC4A
public key `135E426D67D8416DE1D6AC7FFED5BBA38EE0DC4A` pushed to server successfully

This will allow others to verify images that you have signed.

If you delete your local public PGP key, you can always locate and download it again like so.

$ singularity key search Godlove
Search results for 'Godlove'

Type bits/keyID     Date       User ID
pub  4096R/8EE0DC4A 2018-10-08 Dave Godlove (demo) <>

$ singularity key pull 8EE0DC4A
1 key(s) fetched and stored in local cache /home/david/.singularity/sypgp/pgp-public

But note that this only restores the public key (used for verifying) to your local machine and does not restore the private key (used for signing).

Searching for keys

Singularity allows you to search the keystore for public keys. You can search for names, emails, and fingerprints (key IDs). When searching for a fingerprint, you need to use 0x before the fingerprint, check the example:

# search for key ID:
$ singularity key search 0x8883491F4268F173C6E5DC49EDECE4F3F38D871E

# search for the sort ID:
$ singularity key search 0xF38D871E

# search for user:
$ singularity key search Godlove

# search for email:
$ singularity key search

Signing and validating your own containers

Now that you have a key generated, you can use it to sign images like so:

$ singularity sign my_container.sif
Signing image: my_container.sif
Enter key passphrase:
Signature created and applied to my_container.sif

Because your public PGP key is saved locally you can verify the image without needing to contact the Keystore.

$ singularity verify my_container.sif
Verifying image: my_container.sif
Data integrity checked, authentic and signed by:
    Dave Godlove (demo) <>, KeyID FED5BBA38EE0DC4A

If you’ve pushed your key to the Keystore you can also verify this image in the absence of a local key. To demonstrate this, first delete your local keys, and then try to use the verify command again.

$ rm ~/.singularity/sypgp/*

$ singularity verify my_container.sif
Verifying image: my_container.sif
INFO:    key missing, searching key server for KeyID: FED5BBA38EE0DC4A...
INFO:    key retreived successfully!
Store new public key 135E426D67D8416DE1D6AC7FFED5BBA38EE0DC4A? [Y/n] y
Data integrity checked, authentic and signed by:
    Dave Godlove (demo) <>, KeyID FED5BBA38EE0DC4A

Answering yes at the interactive prompt will store the Public key locally so you will not have to contact the Keystore again the next time you verify your container.