LINE Help Center

Letter Sealing is a feature that uses a technology known as end-to-end encryption (E2EE). This prevents any non-members of a chat on LINE, including us, from seeing its contents.

E2EE is a method of communicating that ensures only the sender and recipient can decipher message content. The messages are also stored on servers in an encrypted state. This feature lets users send and receive messages with enhanced security when both sender and receiver have Letter Sealing enabled.
Note: To have Letter Sealing enabled in a group chat, all group members (up to 50 members) need to have Letter Sealing turned on.

Letter Sealing is currently turned on by default so users can exchange messages in chats more securely and safely.

Letter Sealing encrypts:
• Text messages (not including messages sent through other services like YouTube)
• Location information
• 1-on-1 voice/video calls

• Photos/Videos/Voice messages

• Files

Be advised

- Photos, videos, voice messages, and files may not be encrypted depending on your version of LINE and specifications.
- There is no option for disabling Letter Sealing as it is a means of enhancing security and protection on LINE.
- After transferring your LINE account, Letter Sealing may prevent you from viewing messages sent and received in the past. In this case, refer to "This message can't be displayed" appears and I can't see chat messages.

To verify whether Letter Sealing is enabled, follow the steps below and if key fingerprints are visible, it indicates that the feature is active.

Useful info

Key fingerprints are unique encryption keys that Letter Sealing gives to each user so they can send messages to one another safely and securely. The actual keys are kept secret and will not appear in LINE chats. If your key fingerprint matches that of your friend, it means your chat is securely encrypted.

To compare key fingerprints:
1. Tap menu icon

at the top of a chat screen.
2. Tap This chat is protected with Letter Sealing at the bottom of the screen.
Note:

- This won't appear if Letter Sealing is turned off. To enable it, open the LINE app on your smartphone, tap the Home tab > Settings

> Privacy > and turn ON Letter Sealing.

- Tap here to go to Settings from your smartphone.
3. Compare the key fingerprints on your device and your friend's device.
Note: To compare key fingerprints with your friend, we recommend meeting face-to-face or using a form of communication you trust.

What to do if the verification code input screen doesn't appear on the smartphone version of LINE when verifying your identity for Letter Sealing on LINE for PC

Follow the steps below to verify your identity.
Note: You need to verify your identity to send messages on LINE for PC with Letter Sealing enabled on the smartphone version of LINE.

To verify your identity:
1. Restart LINE on your smartphone.
2. Log in to LINE for PC.
3. Open a chat from Chats

on the main menu.
4. Click Verify my identity and get a verification code.
5. Enter the verification code on the identity verification screen that appears in the smartphone version of LINE.

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This Help article covers what happens when you see an error such as "This message can't be displayed" and can't view messages that were sent/received in the past.

Some of these error messages include the following.

- "This message can't be displayed"
- "Unable to display message as it couldn't be decrypted."
- "This message wasn't backed up and restored from your previous device. Unfortunately, there's no way to read it on your current device."

If you've done any of the following, Letter Sealing (a feature that enhances security for sending and receiving messages) will be applied, and you may not be able to view messages that were sent or received in the past.

You transferred your LINE account to a device with the same OS (e.g. iOS to iOS) without backing up and restoring your chats
If you've backed up your chats on your old device before transferring your account, you can view them on your new device.

You transferred your account to a device with a different OS (e.g. iOS to Android)
If you transferred your account to a device with a different OS, you cannot transfer your past chat messages. When transferring your chat history to a device with a different OS, you can transfer your chat history from the last 14 days by using a backup PIN.

You received chat messages while transferring your account
Any chat messages you received from friends while transferring your account cannot be transferred to your new device.

You cannot re-display past messages that can no longer be viewed. If you want to see your past messages, please ask the other person in the chat to resend you any old messages that you need.

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