THE FILE FIELD GUIDE

.asc

ASCII Armor and Other Text Data

Certificates & Keys

ASC is ambiguous: PGP signatures, keys and encrypted data differ from ASCII grids and other text. Identify the producer and header first.

Main use: Signatures, keys, encrypted or other ASCII data
Data type: Multiple uses; identify the producer

All sections, questions and sources

Content reviewed：2026-10-19 · Editor：Kai

Identify the format first

Identify the format first
Clue	Appropriate next step
BEGIN PGP SIGNATURE	Verify with the matching data and public key
BEGIN PGP MESSAGE	Check the intended recipient’s decryption requirements
Other ASCII data	Identify the producer; do not assume OpenPGP

Source for these steps：GnuPG · gpg manual

Opening steps

Choose your environment or purpose to see its steps.

GnuPG for OpenPGP data

Preserve the original and inspect a working copy in a compatible application.

Inspect a copy for a BEGIN PGP header.
For a signature, obtain the signed data and signer’s public key.
Distinguish decryption, verification and key import in GnuPG.

Inspect the received file and its requirements

Establish dependencies and settings before proceeding.

Do not infer encryption/signing from the suffix.
Confirm public-key fingerprints through a trusted independent route.
For GIS data, consult the producing system.

Menu labels and support vary by app, OS and version. Preserve the original before making changes.

Troubleshooting by symptom

Cannot decrypt: distinguish signatures/keys from ciphertext.
Signed data missing: obtain the matching version.
Unknown signer: verify fingerprints.
GIS data fails: identify its format rather than using OpenPGP.

ASC → appropriate verification/decryption

Preserve the original and perform the identified operation.
Reopen the output and check it against the preservation points in this guide before handoff.

A signature may not contain its data; a public key alone cannot decrypt data intended for a private key.

Valid signature versus signer identity

A matching signature still requires confirming whose key was used.

Source for these steps：GnuPG · gpg manual / GnuPG · The GNU Privacy Handbook

Worked example: checks before handoff

Example: verify the release file, key fingerprint and reported signer.

Source for these steps：GnuPG · gpg manual / GnuPG · The GNU Privacy Handbook

Related-format differences

Related-format differences
Format / method	Purpose and preserved information
.asc	Signatures, keys, encrypted or other ASCII data
GPG / P7S	OpenPGP binary / another signature system.
ASC → appropriate verification/decryption	A signature may not contain its data; a public key alone cannot decrypt data intended for a private key.

Handling and security

Protect private keys/passphrases and authenticate public keys.

Questions and answers

Always encrypted?

It also denotes ordinary ASCII data.

Which key can be shared?

Distinguish public/private keys; never publish the private key.

Ignore a bad signature?

Recheck version, data and key.

Format facts: name, steward and MIME type

Formal name: ASCII Armor and Other Text Data
Steward / specification: GnuPG
MIME type: Consult the producer or delivery system. The extension alone does not establish a MIME type.

Primary and official sources

Software documentationgpg manual
Signature verification, decryption and ASCII armor.
GnuPG · Link checked：2026-10-16
Software documentationThe GNU Privacy Handbook
Key handling and signature-verification concepts.
GnuPG · Link checked：2026-10-16