Signedbyetcaptkeyrings

Signedbyetcaptkeyrings refers to the practice of using per-repository GPG keyrings to verify packages in APT, enabled by the signed-by option in repository definitions. This approach ties a repository’s package signatures to a specific keyring file rather than to a system-wide trust store, improving isolation and security when managing multiple sources.

In practice, the signed-by mechanism works by specifying a keyring file in the repository entry, such as deb [signed-by=/etc/apt/keyrings/repo-keyring.gpg] http://example.org/ubuntu focal main. APT then uses the designated keyring to verify the digital signatures on packages from that repository. The keyring file typically resides under /etc/apt/keyrings or a similar path and contains the repository’s public GPG keys in a format compatible with GPG or GnuPG.

Setting up signedbyetcaptkeyrings generally involves:

- Importing or obtaining the repository’s public key and storing it in a dedicated keyring file, for example /etc/apt/keyrings/repo-keyring.gpg.

- Updating the repository definition to include the signed-by option pointing to that keyring.

- Running apt update to fetch metadata and verify package signatures against the specified key.

Security considerations are a primary motivation: using per-repository keyrings minimizes trust to only the keys necessary for a given source and reduces risk if a key is compromised. Apt-key usage is deprecated in favor of the signed-by approach, reinforcing best practices for key management and rotation.

See also: APT, apt-key, deb syntax, /etc/apt/keyrings, Debian/Ubuntu package management.