Before You Begin
After learning how to send encrypted emails, the next crucial skill is properly receiving and decrypting messages sent to you. This guide will walk you through the process of identifying, decrypting, and verifying encrypted messages in Secure Mail Client.
Before proceeding with this module, ensure you have:
- Your PGP key pair correctly set up in Secure Mail Client
- At least one email account connected to the application
- Completed the previous module on sending encrypted emails
Tip
If you haven't received any encrypted emails yet, you can send one to yourself using a second email account as practice. Alternatively, you can use Secure Mail Client's built-in test feature to simulate receiving an encrypted message.
Understanding Encrypted Messages
When someone sends you an encrypted email using PGP, several components work together to ensure security:
Components of an Encrypted Message
Encrypted Content
The message body and attachments are encrypted with a random session key, making them unreadable to anyone without the proper decryption key.
Encrypted Session Key
The session key used to encrypt the content is itself encrypted with your public key, ensuring only you can access it.
Digital Signature
If the sender signed their message, a digital signature is included to verify their identity and ensure the message hasn't been tampered with.
Email Wrapper
The encrypted content is delivered in a standard email, which includes unencrypted headers (subject line, sender, recipient, date).
Security Alert
Remember that email headers, including the subject line, are never encrypted with PGP. This is why security-conscious senders often use generic subject lines for sensitive communications.
Identifying Encrypted Emails
When you receive an encrypted email, Secure Mail Client will automatically identify it. Here's how to recognize encrypted messages in your inbox:
Visual Indicators
- Look for a lock icon next to the email in your inbox list
- Encrypted emails may have a different background color or border
- Some versions of Secure Mail Client automatically add an "Encrypted" tag
- A security status indicator may appear in the message header
Content Appearance
- Before decryption, the message body will show encrypted content (a block of seemingly random characters)
- You may see PGP message markers like "-----BEGIN PGP MESSAGE-----"
- Encrypted attachments may show a special icon or indicator
- A prompt or button to decrypt will be visible
The Decryption Process
Decrypting an encrypted email in Secure Mail Client is typically straightforward. Here's the step-by-step process:
- 1
Open the encrypted email
Select the encrypted message from your inbox to view it
Note:
Secure Mail Client will display a notification that the message is encrypted and needs to be decrypted before viewing.
- 2
Initiate decryption
Click the "Decrypt" button or similar option in the message header
Decrypt Message
Verify Signature
View Raw Message
- 3
Enter your passphrase
If prompted, enter the passphrase for your private key
Passphrase Required
Enter the passphrase to unlock your private key - 4
View the decrypted message
The encrypted content will be decrypted and displayed in readable form
Message successfully decrypted and signature verifiedHello,
This is your decrypted message. The content is now readable because your private key was able to decrypt the session key that was used to encrypt this message.
Thank you for using PGP encryption!
- 5
Check signature verification status
Verify the digital signature to confirm the sender's identity and message integrity
Valid Signature
Unknown Key
Invalid Signature
Understanding Signature Verification
Digital signatures provide two important security benefits: they confirm who sent the message and verify that the message hasn't been altered since it was signed. Here's what different verification statuses mean:
Valid Signature
The message was signed by the claimed sender and hasn't been altered
When you see this status, you can be confident that:
- The message came from the owner of the private key corresponding to the verification key
- No one has changed the message content since it was signed
- You have the sender's public key in your keyring and trust it
Unknown Key / Unverified Signature
The message contains a signature, but you don't have the sender's public key or haven't verified it
This status means:
- The signature mathematics check out, but you can't verify who the key belongs to
- You need to obtain the sender's public key from a trusted source to fully verify
- The message integrity is verified, but the sender's identity isn't confirmed
Invalid Signature
The signature is not valid - this is a serious warning
This status indicates:
- The message may have been tampered with after it was signed
- The signature doesn't match the claimed sender
- There could be an attempt to forge communication
- Treat the message content with extreme caution
No Signature
The message was not digitally signed
This means:
- The message was encrypted for you, but not signed by the sender
- You can read the content, but cannot cryptographically verify who sent it
- The lack of a signature doesn't mean the message is malicious, but you have less security assurance
Security Alert
Always pay attention to signature verification status. Be extremely cautious about acting on instructions in a message with an invalid signature, especially if it involves sensitive information or financial transactions.
Handling Encrypted Attachments
Encrypted emails may also contain encrypted attachments. Here's how to handle them:
- 1
Automatic decryption: In most cases, Secure Mail Client will automatically decrypt attachments when you decrypt the message body.
- 2
Manual decryption: If an attachment remains encrypted, you may need to right-click it and select "Decrypt" from the context menu.
- 3
Save decrypted files: You can save the decrypted attachment to your computer by using the "Save As" option.
- 4
Verify attachment signatures: Some attachments may have their own signatures, which can be verified separately.
Security Considerations for Attachments
Scan for malware: Even when received from trusted sources, it's good practice to scan decrypted attachments with antivirus software before opening them.
Temporary storage: Be aware that decrypted attachments may be temporarily stored on your device. Choose secure storage locations for sensitive files.
Secure handling: If you're saving highly sensitive decrypted files, consider using encrypted storage solutions for long-term storage.
Troubleshooting Decryption Issues
Sometimes you may encounter issues when trying to decrypt messages. Here are common problems and their solutions:
Private Key Not Found
The application cannot find the private key needed to decrypt the message.
Solutions:
- Verify that your private key is properly imported into Secure Mail Client
- Check if the message was encrypted to a different key you may have
- Ensure the email address on your key matches the one used for encryption
- Import your private key if you're using a new device or after a fresh installation
Incorrect Passphrase
The system cannot unlock your private key because the passphrase entered is incorrect.
Solutions:
- Double-check your passphrase for typing errors
- Try alternative passphrases if you use several
- Check if caps lock is on or if your keyboard layout has changed
- If you've forgotten your passphrase, you'll need to use a backup of your key or a key recovery method if available
Corrupted Message
The encrypted message format is damaged or incomplete.
Solutions:
- Ask the sender to re-send the message
- Check if something altered the message format (e.g., some email systems may modify line breaks)
- Try viewing the raw message and look for complete PGP message blocks
- If the message was copied and pasted, ensure the entire PGP block was included
Key Expired or Revoked
The encryption key used is no longer valid.
Solutions:
- If your key has expired, you may still decrypt messages (in most PGP implementations)
- If the sender used a revoked key, inform them to use your new public key
- Update your keys in key servers if you've renewed them
- Send your updated public key to frequent correspondents
Tip
If you're experiencing persistent decryption issues, check Secure Mail Client's logs (usually found in Settings > Advanced > View Logs). They often contain detailed information about what's going wrong during the decryption process.
Best Practices for Handling Encrypted Messages
To maintain security when receiving and decrypting messages, follow these best practices:
Security Practices
- Keep your private key secure and passphrase confidential
- Always verify signatures before acting on important messages
- Be cautious with messages having invalid signatures
- Disable automatic decryption on shared computers
- Lock your computer when stepping away, even briefly
Organizational Habits
- Maintain an updated key backup in a secure location
- Regularly update your keyring with current public keys
- Consider separate encryption keys for different contexts
- Set reminders for key expiration dates
- Periodically review key trust settings in your keyring
Advanced Features
As you become more comfortable with basic decryption, explore these advanced features in Secure Mail Client:
Automatic Key Retrieval
Configure Secure Mail Client to automatically look up unknown keys on public key servers when verifying signatures.
Trust Management
Use the key management interface to assign trust levels to different keys, making verification more nuanced.
Message Filters
Create filters that automatically handle encrypted messages, such as moving verified messages to specific folders.
Multi-Device Synchronization
Set up key synchronization across multiple devices while maintaining security.
Conclusion
Successfully decrypting and verifying encrypted emails is a fundamental skill for secure communication. With Secure Mail Client's intuitive interface, the process is straightforward, but understanding the underlying principles helps you make informed security decisions.
As you continue using encrypted email, you'll develop a better feel for managing keys, verifying signatures, and handling encrypted communications efficiently. With practice, these processes will become second nature.
In the next module, we'll explore how to create and manage digital signatures for your emails, providing recipients with verification of your identity even when full encryption isn't needed.
Key Takeaways
- Secure Mail Client automatically identifies encrypted messages in your inbox
- Decryption requires your private key and passphrase
- Digital signatures verify both the sender's identity and message integrity
- Pay close attention to signature verification status indicators
- Follow security best practices when handling decrypted content