Signing and Verifying Containers
Singularity 3.0 introduced the ability 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.
Note
Singularity 3.6.0 uses a new signature format. Containers signed by 3.6.0 cannot be verifed by older versions of Singularity.
To verify containers signed with older versions of Singularity using 3.6.0
the --legacy-insecure flag must be provided to the singularity verify command.
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:
Go to: https://cloud.sylabs.io/
Click “Sign In” and follow the sign in steps.
Click on your login id (same and updated button as the Sign in one).
Select “Access Tokens” from the drop down menu.
Enter a name for your new access token, such as “test token”
Click the “Create a New Access Token” button.
Click “Copy token to Clipboard” from the “New API Token” page.
Run
singularity remote loginand paste the access token at the prompt.
Now you can verify containers that you pull from the library, ensuring they are bit-for-bit reproductions of the original image.
$ singularity verify alpine_latest.sif
Container is signed by 1 key(s):
Verifying partition: FS:
8883491F4268F173C6E5DC49EDECE4F3F38D871E
[REMOTE] Sylabs Admin <support@sylabs.io>
[OK] Data integrity verified
INFO: Container verified: alpine_latest.sif
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) : David Trudgian
Enter your email address (e.g., john.doe@example.com) : david.trudgian@sylabs.io
Enter optional comment (e.g., development keys) : demo
Enter a passphrase :
Retype your passphrase :
Would you like to push it to the keystore? [Y,n] Y
Generating Entity and OpenPGP Key Pair... done
Key successfully pushed to: https://keys.sylabs.io
Note that I chose Y when asked if I wanted to push my key to the
keystore. This will push my public key to whichever keystore has been
configured by the singularity remote command, so that it can be
retrieved by other users running singularity verify. If you do not
wish to push your public key, say n during the newpair
process.
The list subcommand will show you all of the keys you have created or saved
locally.`
$ singularity key list
Public key listing (/home/dave/.singularity/sypgp/pgp-public):
0) U: David Trudgian (demo) <david.trudgian@sylabs.io>
C: 2019-11-15 09:54:54 -0600 CST
F: E5F780B2C22F59DF748524B435C3844412EE233B
L: 4096
--------
In the output above the index of my key is 0 and the letters stand
for the following:
U: User
C: Creation date and time
F: Fingerprint
L: Key length
If you chose not to push your key to the keystore during the newpair process, but later wish to, you can push it to a keystore configured using singularity remote like so:
$ singularity key push E5F780B2C22F59DF748524B435C3844412EE233B
public key `E5F780B2C22F59DF748524B435C3844412EE233B` pushed to server successfully
If you delete your local public PGP key, you can always locate and download it again like so.
$ singularity key search Trudgian
Showing 1 results
KEY ID BITS NAME/EMAIL
12EE233B 4096 David Trudgian (demo) <david.trudgian@sylabs.io>
$ singularity key pull 12EE233B
1 key(s) added to keyring of trust /home/dave/.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 @gmail.com
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
[LOCAL] Signing entity: David Trudgian (Demo keys) <david.trudgian@sylabs.io>
[LOCAL] Fingerprint: 65833F473098C6215E750B3BDFD69E5CEE85D448
Objects verified:
ID |GROUP |LINK |TYPE
------------------------------------------------
1 |1 |NONE |Def.FILE
2 |1 |NONE |JSON.Generic
3 |1 |NONE |FS
Container verified: my_container.sif
If you’ve pushed your key to the Keystore you can also verify this
image in the absence of a local public key. To demonstrate this,
first remove your local public key, and then try to use the
verify command again.
$ singularity key remove E5F780B2C22F59DF748524B435C3844412EE233B
$ singularity verify my_container.sif
Verifying image: my_container.sif
[REMOTE] Signing entity: David Trudgian (Demo keys) <david.trudgian@sylabs.io>
[REMOTE] Fingerprint: 65833F473098C6215E750B3BDFD69E5CEE85D448
Objects verified:
ID |GROUP |LINK |TYPE
------------------------------------------------
1 |1 |NONE |Def.FILE
2 |1 |NONE |JSON.Generic
3 |1 |NONE |FS
Container verified: my_container.sif
Note that the [REMOTE] message shows the key used for verification
was obtained from the keystore, and is not present on your local
computer. You can retrieve it, so that you can verify even if you are
offline with singularity key pull
$ singularity key pull E5F780B2C22F59DF748524B435C3844412EE233B
1 key(s) added to keyring of trust /home/dave/.singularity/sypgp/pgp-public
Advanced Signing - SIF IDs and Groups
As well as the default behaviour, which signs all objects, fine-grained control of signing is possible.
If you sif list a SIF file you will see it is comprised of a
number of objects. Each object has an ID, and belongs to a
GROUP.
$ singularity sif list my_container.sif
Container id: e455d2ae-7f0b-4c79-b3ef-315a4913d76a
Created on: 2019-11-15 10:11:58 -0600 CST
Modified on: 2019-11-15 10:11:58 -0600 CST
----------------------------------------------------
Descriptor list:
ID |GROUP |LINK |SIF POSITION (start-end) |TYPE
------------------------------------------------------------------------------
1 |1 |NONE |32768-32800 |Def.FILE
2 |1 |NONE |36864-36961 |JSON.Generic
3 |1 |NONE |40960-25890816 |FS (Squashfs/*System/amd64)
I can choose to sign and verify a specific object with the --sif-id option
to sign and verify.
$ singularity sign --sif-id 1 my_container.sif
Signing image: my_container.sif
Enter key passphrase :
Signature created and applied to my_container.sif
$ singularity verify --sif-id 1 my_container.sif
Verifying image: my_container.sif
[LOCAL] Signing entity: David Trudgian (Demo keys) <david.trudgian@sylabs.io>
[LOCAL] Fingerprint: 65833F473098C6215E750B3BDFD69E5CEE85D448
Objects verified:
ID |GROUP |LINK |TYPE
------------------------------------------------
1 |1 |NONE |Def.FILE
Container verified: my_container.sif
Note that running the verify command without specifying the specific sif-id
gives a fatal error. The container is not considered verified as whole because
other objects could have been changed without my knowledge.
$ singularity verify my_container.sif
Verifying image: my_container.sif
[LOCAL] Signing entity: David Trudgian (Demo keys) <david.trudgian@sylabs.io>
[LOCAL] Fingerprint: 65833F473098C6215E750B3BDFD69E5CEE85D448
Error encountered during signature verification: object 2: object not signed
FATAL: Failed to verify container: integrity: object 2: object not signed
I can sign a group of objects with the --group-id option to sign.
$ singularity sign --groupid 1 my_container.sif
Signing image: my_container.sif
Enter key passphrase :
Signature created and applied to my_container.sif
This creates one signature over all objects in the
group. I can verify that nothing in the group has been modified by
running verify with the same --group-id option.
$ singularity verify --group-id 1 my_container.sif
Verifying image: my_container.sif
[LOCAL] Signing entity: David Trudgian (Demo keys) <david.trudgian@sylabs.io>
[LOCAL] Fingerprint: 65833F473098C6215E750B3BDFD69E5CEE85D448
Objects verified:
ID |GROUP |LINK |TYPE
------------------------------------------------
1 |1 |NONE |Def.FILE
2 |1 |NONE |JSON.Generic
3 |1 |NONE |FS
Container verified: my_container.sif
Because every object in the SIF file is within the signed group 1 the entire
container is signed, and the default verify behavior without specifying
--group-id can also verify the container:
$ singularity verify my_container.sif
Verifying image: my_container.sif
[LOCAL] Signing entity: David Trudgian (Demo keys) <david.trudgian@sylabs.io>
[LOCAL] Fingerprint: 65833F473098C6215E750B3BDFD69E5CEE85D448
Objects verified:
ID |GROUP |LINK |TYPE
------------------------------------------------
1 |1 |NONE |Def.FILE
2 |1 |NONE |JSON.Generic
3 |1 |NONE |FS
Container verified: my_container.sif