Verify and Inspect a Message

When you get a message, you want to know two things:

Can I trust it? Did it really come from the sender, and was it changed on the way?
Can I read it? If it is encrypted, do you have the key to open it?

This page shows where GpgFrontend answers these questions.

On a Mac, press Cmd where this page says Ctrl.

Open the Message

Open the message in a mail tab. You can:

open an .eml file, for example from the File Panel, or
fetch it from your mail server. See Read Mail from Your Server.

Read the Security Badge

At the right end of the action row there is a status button. We call it the badge. It tells you, in a few words, what kind of message this is. Click it to open the Security menu.

Badge	What it means
Not signed or encrypted	An ordinary message. Nothing proves who sent it. This is normal for most email.
Encrypted	The message is hidden. It has no signature.
Signature not checked	The message has a signature, but it has not been checked yet. This says nothing good or bad so far.
Encrypted, signature not checked	The same, for an encrypted message.
Signature verified	The signature was checked and it is good. The message was not changed since it was signed.
Encrypted, signature verified	The same, for an encrypted message.
Signed by a different address	The signature is good, but the key belongs to a different address than the one in From. Be careful.
Signature or key expired	The signature matches, but the signature or the key has expired.
Signed by an unknown key	You do not have the sender’s public key, so the signature cannot be checked. Import their key, then check again.
Signature could not be checked	The check ran, but it could not give an answer. Trying again may help.
Signing key not authorized	The signature is correct, but the key that made it is not allowed to sign. Do not trust it.
Bad signature	The signature does not match the message, or the key was revoked. The message may have been changed. Do not trust it.
Malformed OpenPGP structure	The message says it uses OpenPGP, but it is not built the right way. It may not verify or decrypt.

Check the Signature

A signature is not checked by itself when you open a message. To check it:

Click the badge.
Click Verify Signature.

For an encrypted and signed message, click Decrypt and Verify instead.

The badge changes to show the result. The details also appear in the Status Panel.

Can I Open This Encrypted Message?

When a message is encrypted, the body is hidden. In its place you see a panel that says This message is encrypted (or This message is encrypted and signed). Below it, GpgFrontend tells you what it knows:

Addressed to …: who the message was sent to, from its headers.
Whether you hold the right private key. For example: “You hold the private key for [email protected], so this message can be opened here.”
If you do not: “This message is encrypted to keys you do not hold the private half of, so it cannot be opened on this computer.”
Sometimes it cannot tell. Some senders hide who the message is for. Then the only way to know is to try.

To open it, click Decrypt on the panel.

The Message Details Window

The Message Details window shows everything GpgFrontend knows about a message. To open it, do one of these:

Click More > Details….
Press Ctrl+Shift+D.
Click the badge, then a details item, such as Signature Details… or Encryption Details….

The window has three tabs.

Security

The top line says what the message is, for example This message carries a signature. Below it are up to four groups:

Signatures: each signature, who made it, and whether it is good. You also see the key Fingerprint, when it was signed (Signed at), and the hash method used.
Recipients: for an encrypted message, who it was encrypted to.
Keys for these addresses: for each address in the message, which keys you have for it and whether they are usable. no key found means you have no key for that address.
What stands out: things worth knowing about this message. See the list below.

Right-click a row for more actions:

Copy Value, Copy Fingerprint, Copy Address.
Import the Key in This Message: when you have no key for an address, but the message carries one.
Verify Signatures (or Verify Again): check the signatures now.

Structure

An email is built from parts: the text, any attachments, and the signature. This tab lists every part, with its Name, Size and Encoding.

The Covered by column says which signature protects each part. not covered means that part is outside the signature. Anyone could have added or changed it.

Right-click a part to Save Part…, Import This Key (if it is a key), Copy Content-Type, Copy Name or Copy SHA-256.

Headers

Headers are the lines at the top of an email, such as From, To, Date and Subject. This tab lists all of them, with their Name and Value.

Type in Filter headers to show only the headers that contain some text. Right-click a header to Copy Value or Copy Whole Field.

Warnings in “What Stands Out”

These are the warnings you may see, in plain words:

Signed part no longer in canonical form: a program changed the message after it was signed, usually the line endings. The signature may fail even though nobody meant harm.
Duplicate … header: a header that should appear once appears more than once. Different email apps may show different values.
Address may be disguised: an address uses letters that can look like a different, familiar address. Check it closely.
Replies go somewhere else: if you reply, your answer goes to a different domain than the sender’s.
Malformed signed section or Malformed encrypted section: the message is not built the right way.
Not everything is signed: some parts are outside the signature. Anyone could have added them.
Signature covers the encrypted data only: the signature shows who sent the encrypted block, not who wrote what is inside. Anyone can sign a copy of someone else’s encrypted message.
Public key attached: the message carries a public key. A key in a message proves nothing about who sent it. Anyone can make a key with any name.
Detached signature attached: the message carries a signature file for something else. Opening the message does not check it.
Blind recipients are visible: the message has a Bcc header, so every reader can see who got a secret copy.

Check Before Exporting

When you save a message to an .eml file, GpgFrontend takes a last look at it. If it finds a real risk, a Check before exporting window opens. It says: “Something about this message is worth checking before you save it.” and lists what it found.

It can warn you about:

Bcc header present: the message has a Bcc header. Sending it would tell every reader who got a secret copy.
Recipient may be disguised: an address uses letters that can look like a different address. Check it before sending.

Smaller notes, such as Some parts are not signed or No recipients, are under the details button in the same window.

You decide what to do:

Click Save to save the file anyway.
Click Cancel to go back and fix the message.

Cancel is the default, so pressing Enter does not save by accident.

HTML Messages Are Shown as Source

Some messages are written in HTML, the language of web pages. GpgFrontend never draws them as a web page. It shows the HTML code as plain text instead, with this notice: “This message was written in HTML. It is shown as its source rather than rendered: nothing here loads images or follows links.”

This is safer:

No hidden tracking. Images in an email can tell the sender when and where you opened it. Here, no images are loaded.
No surprise links. Nothing opens a website on its own.
What you see is what is there. HTML can hide text, or make one link look like another. As plain text, nothing is hidden.

Messages Are Checked Again When Your Keys Change

A check result depends on the keys you have. So GpgFrontend checks open messages again when:

you import a key, for example the sender’s public key, or
you switch or reload your key databases.

For example, a message that said Signed by an unknown key can turn into Signature verified right after you import the sender’s key.