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Letter Sealing is an encryption technology that prevents any non-members of a chat on LINE, including us, from seeing the contents of its messages.

Topics covered
- About Letter Sealing
- Information Letter Sealing is applied to
- Confirming if Letter Sealing is enabled
- Verifying your identity on secondary devices

About Letter Sealing:
Letter Sealing uses a technology called end-to-end encryption.

End-to-end encryption is a communication method that makes it so that only the sender and receiver of a message can decrypt its content. Message content is saved in an encrypted state on the server, as well. When both the sender and receiver of a message have Letter Sealing turned on, the message can be sent and received with greater security using this feature.

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

Information Letter Sealing is applied to:
Letter Sealing encrypts the following information sent as messages.

Useful info

To have Letter Sealing enabled in a group chat, all group members (up to 50 members) need to have Letter Sealing turned on.

• Text messages (not including messages sent through other services like YouTube)
• Location information
• Photos/Videos/Voice messages
• Files
• Voice/video calls in 1-on-1 chats
Note:
- Letter Sealing is not applied to voice/video calls in group chats.
- Albums and notes have server-side encryption (SSE) applied, not Letter Sealing.

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.

Confirming if Letter Sealing is enabled:
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 the key fingerprints you and your friend see match, it means your messages are securely encrypted.

1. Tap

at the top of the chat.
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 main device, tap the Home tab >

> Privacy > and turn ON Letter Sealing.
- Tap here to go to Settings from your main device.
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.

Verifying your identity on secondary devices:
If you use LINE on a secondary device after turning on Letter Sealing, you'll be required to verify your identity the first time you send a message by entering a verification code on LINE on your main device.

If you do not see the verification code entry screen on LINE on your main device, verify your identity again with the steps below.
Note: To send messages with LINE on your secondary device with Letter Sealing turned on in LINE on your main device, you need to verify your identity.

1. Restart LINE on your main device.
2. Log in to LINE on your secondary device.
3. Open a chat from Chats

on the main menu.
4. Select Verify my identity and get a verification code.
5. Enter the verification code shown on your secondary device on the identity verification screen that appears in LINE on your main device.

See also:
"This message can't be displayed" appears and I can't see chat messages
Privacy protections for your registered information and chats

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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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