How to sign a file or message using gpg?

Many businesses are responsible for maintaining large amounts of confidential data, including customer records, medical records, financial reports, sensitive documents, and much more. It’s very common for these types of information to be transmitted via email or other services. So how can you ensure confidential data transmitted via email is kept private? How can you ensure the integrity of transmitted data?

GnuPG offers three options for signing data:

Create binary or ASCII-armored detached signature from input

Wrap input in plaintext signature

Encode input into binary or ASCII-armored output with an integrated signature

Let's take a simple example of how to sign a document.

Signed file is saved as file.txt.asc and this is the content:

Then you need to verify signed file:

You will see something like this:

A signed document has limited usefulness. Other users must recover the original document from the signed version, and even with clearsigned documents, the signed document must be edited to recover the original. Therefore, there is a third method for signing a document that creates a detached signature. A detached signature is created using the --detach-sig option.

Both the document and detached signature are needed to verify the signature. The --verify option can be to check the signature.