Home

Hong. (2011) conducted a research for a method to determine whether the location information included in the image file was manipulated, or not whether the image itself was manipulated[3]. In general, the location information is included in the Exif of the image file, and it is saved when the pictured is taken[3]. In this study, the four methods on manipulation detection of Exif information in image files were proposed[3].

Orozco. (2015) investigated a classification of 10 types of error in Exif data, which is saved when the picture is taken on the mobile phone[4]. This paper showed the anomalies in the Exif, which can produce serious problems in classical tools for the extraction of image metadata, including crashes and wrong results, and even interoperability problems among different devices[4]. The experimental results indicated that many of the manufacturers doesn't follow the Exif specification. Through the experimental results of this paper, it reminds us of the need to accumulate Exif-related database to idenfity and detect the anomalies in the Exif.

Bae. (2018) proposed an audio watermarking methodology for copyright protection of high-equality stereo music[5]. In this paper, this methodology was generated with two kinds of information, "Copyright" and "Copy_free" by using the turbo code[5]. The proposed algorithm is implemented to efficiently detect watermarks when stereo music is converted to mono[5].

Kim. (2019) proposed a robust watermarking method suitable for small content by using orthogonal watermark set[6]. In this paper, the processing time required to search all codebooks for watermark detection in the existing information-using watermarking method was shortened by using a simple echo signal as a pilot signal.

Kim et al. (2016) proposed a video metadata database to prove that a video shot by an individual with a smartphone was taken from the dedicated smartphone[2]. For this system, a database server was built for metadata search and tracking, and applications for Android and iPhone were developed[2].

The researches that we reviewed and explained above have the same direction in that they trace and track the source of media files such as image, audio and video file. However, there are inconveniences such as that a database server is needed to be built or that some dedicated systems are needed. Moreover, as data is being filed up, there’s a risk of data exposure.

In this paper, we propose a method to trace and track the source of sharing data without external databases. The proposed method of this paper is built-in to smartphones, and add the encrypted information such as distributor to Exif metadata.

The proposed method of this paper is developed as an Android application with the environmental conditions as Table 1. The target devices are LM-V500N and LM-G910N based on Android 10, and the IDE(Integrated Development Environment) for the application is Android Studio based on Java

The Exif format defines a set of TIFF(Tagged Image File Format) tags to describe the images[3]. EXIF data starts from ASCII character “Exif” and 2 bytes of 0x00. On the Android platform, there are dozens of data types which can be stored as the Exif metadata[4]. In this paper, only one tag of Table 2, whose tag name is TAG_MAKER_NOTE, to store the unique phone information to Exif metadata is used.

The Exif metadata is filled with the phone information when the smartphone user tries sending the dedicated file to another device. The data which is inserted into the Exif and the permissions for them are as Table 3.

First, the date when the smartphone user tries sending the dedicated file to another device is used to fill up the Exif. This is to keep the share date on which the file was shared. There's no specific permission to access the data.

Second, some unique information is needed to identify the owner of the smartphone. However, as of Android 10, access to the IMEI(International Mobile Equipment Identity) is not permitted. Therefore, the phone number is used for the unique information, which identifies the owner of the smartphone, instead. To access the phone number, there should be two of permissions that the application should achieve. The first one is "READ_PHONE_NUMBERS", and the second one is "READ_PHONE_STATE".

Finally, this application needs an access to read and write files in the external storage when handling the exif metadata. The related permissions are also needed as followings: "WRITE_EXTERNAL_STORAGE" and "READ_EXTERNAL_STORAGE"[7].

The plaintext of the file sender information is as shown Fig. 1. The first 6 characters are filled with year, month and day, two each. Then, the phone number including the country code is appended after the date.

Fig. 1. 
Format of the fIle sender information

Before sending the file with the inserted private sender information, the inserted data should be encrypted for security. This is because if the data is not encrypted, there is a risk of data falsification, etc.

There are many encryption algorithms such as AES, RC4 and SHA. In the proposed application of this paper, it should be regarded that encrypted data must be decrypted for traceability. For example, the SHA-256 which was introduced in 2001 by the National Institute of Standards and Technology (NIST) algorithm is one of the commonly used ones for data encryption[8]. However, the encrypted data by the SHA-256 can’t be decrypted.

In this paper, therefore, the proposed method uses the AES-256 algorithm to encrypt and decrypt the file sender information. The AES(Advanced Encryption Standard) is an SP-network that supports key sizes of 128 ~ 256 bits[9]. The keys for encryption and decryption are the same. In this paper, the key for encryption and decryption is set as “01234567012345670123456701234567”.

Fig. 2 shows the application interface based on Android. There is a list of the files which are stored in the external storage of the smartphone. Above the file list, there's a text box which shows the Exif metadata before and after inserting the encrypted private sender information into the Exif. After long-clicking on the file, the Exif metadata is updated with the private sender information, and the application shows the menu to choose the application to share the file.

Fig. 2. 
Developed Android application

The working flow of the application is as shown Fig. 3. First, the smartphone user executes the application to share a file. Second, the user selects a file to share. Third, the user long-clicks on the chosen file.

Fig. 3. 
Working flow of the proposed application

Then, the encrypted information is added to the JPEG file as the Exif metadata as long as long-clicking on the file when showing the menu to choose the application to share the dedicated file. Finally, the dedicated file is shared by the chosen application through the Android frameworks system.