New generation of safe messaging: “Letter Sealing”

by LINE Engineer on 2015.10.13

Hello, my name is JI and I am working at LINE as a security engineer.

People might have wondered how safe mobile applications are. Message security is surely something most of you have thought about before. As we are centered around mobile messaging, all the engineers at LINE do take extra care to make our app even safer. But when companies are asked about how safe their message transfer process actually is, not many mobile messaging app companies are able to clearly explain about their security.

Today, I proudly present the newest security feature called “Letter Sealing.” A new feature added in version 5.3.0 of LINE.

Safe delivery of messages

Since time immemorial, methods to transfer secrets between one another have existed, and were an important part of human history. People would whisper secrets in dark alleyways or sometimes even devise a code to prevent any potential eavesdroppers from understanding what they were saying.

However, these methods would only work if the speaker and listener were in close proximity. Without the advanced internet technology that lets us easily communicate long-distance, people in the past had to put their messages into envelopes and deliver them by conventional means. Only, there was one problem: the envelope could be intercepted during delivery and resealed once read, unbeknownst to the actual intended recipient. Even when messages were altered or falsified, the recipient had no way of knowing. You can imagine how difficult it must have been for a message to be sent and received safe and sound.

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True Delete

by LINE Engineer on 2015.8.13

Hello, I am H2spice. I work in security development here at LINE.

This post will cover how your data can be leaked if your mobile device is stolen, and what we at LINE are doing to prevent that: a new feature called “True Delete.”

There are many instances where people lose their mobile devices, or leave their devices unattended in places where anyone can access them. Many serious problems may arise if someone else obtains your mobile device and gains access to the information inside. Devices like your smartphone contain information such as call records, messages, contacts, schedules, browsing history, navigational data, photos, memos and so on. Information leaks like this can lead to an invasion of your privacy, or a breach of confidential company information in some cases. There have been reports where thieves would steal mobile devices for this exact purpose. While our mobile devices bring us great convenience, one mistake and they can be used against you.

LINE has various features that can protect your privacy such as a Passcode Lock, data encryption, and Hidden Chat to name a few. Even with these features however, there is still some room for improvement. One limitation is due to how deleted data can be restored due to how “deletion” works in programming.
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Introducing the LINE Bug Bounty Program

by LINE Engineer on 2015.8.5

Hello. I am MJ from the LINE Security Department. In this post, I would like to announce the details of the LINE Bug Bounty.

What is a bug bounty?

Companies use bug bounty programs to strengthen their services and products by rewarding users that can find vulnerabilities in them. Many companies have used these programs to take a more active role in strengthening the security of their services.

LINE has grown as a global company that now provides services to more than 2 hundred million active users on a monthly basis. The number of products and services have increased, and so have the number of users that require protection. We at LINE aim to provide a more stable service as a result of this bug bounty.

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Introducing the LINE Login Platform

by LINE Engineer on 2015.7.24

LINE publicly released its Login Platform on June 30, 2015, allowing other services to take advantage of its robust features. In this article, we look at the details of the newly released LINE Login Platform. We are also pleased to introduce the LINE developers site to the public. It’s packed with everything you’ve ever wanted to know about the technical side of LINE, so check it out to see all of the features the platform has to offer!

What is the LINE Login Platform?

The LINE Login Platform lets developers who create mobile apps and web applications offer a way for users to log into their apps using their LINE account. There are already many mobile and web apps out on the market that utilize the login features of the LINE Login Platform. In this article, we will take a closer look at Popcorn Buzz and LINE STORE to see exactly how they use this powerful platform.

Popcorn Buzz: LINE Login Platform for Mobile Apps

Popcorn Buzz is a free app for Android and iOS which provides a group calling service that lets users talk to up to 200 people at the same time. Developers usually use a screen like the one shown below when integrating the login feature into a mobile app like Popcorn Buzz. The login screen displays a “Log in with LINE” button that calls the login feature of the LINE Login Platform the moment the user taps it. If the user has the LINE app installed on their device, it automatically takes them to a second screen where they are asked to confirm that they want to log in with LINE. The login process is over before the user has a chance to blink. The superior login functionality offered by the LINE Login Platform leads to a better overall user experience on many apps the world over. 1 Read more

Improving Call Quality On Popcorn Buzz, A Multi-user Call Service

by LINE Engineer on 2015.7.2

We are IG and JN, and we work in the mobile VoIP development department at LINE.
In this post, we would like to talk about what we have done to improve the call quality on the newly launched Popcorn Buzz.


Popcorn Buzz is a group call service that enables up to 200 users to call simultaneously over the internet. Popcorn Buzz users will be able to gather in a virtual space like the one you see below. They will be able to talk to each other, or even hold large-scale conference calls and such.


< Figure 1: Popcorn Buzz service diagram >

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Analyzing Large Amounts of Security Data With Spark, Mesos, Zeppelin, and HDFS

by LINE Engineer on 2015.6.3

Hello, we are WJ and KH and we are in charge of game security development at LINE.

A massive number of players play LINE Games at any given time, and that is why quick issue analysis and response can be difficult. With the large increase in LINE Game players and users from abroad, many instances of abuse (profiting through unauthorized actions) are being observed. Abusing the system affects other players that are playing the game by the rules, while also directly affecting the game itself. Responding to these abuses as quickly as possible is crucial to keeping the game stable, and to protect players that are playing the game as intended.
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LINE DEVELOPER DAY_2015 Videos and Slides

by LINE Engineer on 2015.5.14

Hello, my name is K. I was in charge of organizing this year’s conference. As announced in the LINE DEVELOPER DAY_2015 Tokyo Announcement « LINE Engineers' Blog post, the LINE DEVELOPER DAY_2015 conference was held on April 28th, 2015.

There were so many people that signed up for the conference, we could not invite everyone. But thanks to all the engineers that showed interest in the event, the conference was a huge success. We would like to express our sincere gratitude!
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