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Account-key assertion

The account-key assertion holds a public key belonging to an account.

This assertion is used to transmit key information between the store and snapd, enabling the latter to validate assertions signed by the key owner.

Alongside account, snap-declaration and snap-revision assertions, account-key is bundled within the composite .assert file that accompanies a snap downloaded with the snap download <snap-name> command.

The make-system-user snap can is used to create a composite assertion file which includes all of the required assertions needed to trigger automatic creation of a user account via an inserted USB drive containing this file. See make-system-user for more details.

Account-key assertion fields

The following fields can be used in an account-key user assertion:

type:                account-key
authority-id:        <authority account id>
revision:            <int>
public-key-sha3-384: <key id/sha3-384 digest of the key>
account-id:          <account id>
name:                <human readable key name>
since:               <UTC datetime>
until:               <UTC datetime>
sign-key-sha3-384:   <key id> # Encoded key id of signing key

BODY: base64 encoded version prefixed public key packet

<signature>                 # Encoded signature

The index for this assertion is public-key-sha3-384. The key is valid in the time interval specified by since and until, being valid forever if the optionaluntil is undefined.

  • public-key-sha3-384 is the SHA3-384 hash of the (decoded) body content. The body itself is a format version byte (0x1 for now) followed by the public key packet itself. The version 1 public key packet is a constrained/normalised RFC4880 public key packet (v4, new header format, algorithm fixed to RSA, timestamp fixed as well).

    The digest of the public key (public-key-sha3-384) is used for the lookup of keys when verifying signatures: all assertions reference their signing key by providing this digest in a sign-key-sha3-384 header.

  • since and until are required when a password is embedded within the assertion. They define the from date and the to date for they key’s validity. They need to be in UTC.

In addition to the signature validation that’s performed for all assertions, it’s essential for the account-key assertion that the digest of the public key matches the assertion body.

See Assertion format for more details on fields common to most assertions.

Example assertion

The following is Canonical’s public key for the store:

type: account-key
authority-id: canonical
revision: 2
public-key-sha3-384: BWDEoaqyr25nF5SNCvEv2v7QnM9QsfCc0PBMYD_i2NGSQ32EF2d4D0hqUel3m8ul
account-id: canonical
name: store
since: 2016-04-01T00:00:00.0Z
body-length: 717
sign-key-sha3-384: -CvQKAwRQ5h3Ffn10FILJoEZUXOv6km9FwA80-Rcj-f-6jadQ89VRswHNiEB9Lxk


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