Abstract
Problems that often occur in internet services make data security not guaranteed. To provide content authentication and duplicate protection from digital data, two complementary techniques have been developed, namely encryption and watermarks. Encryption techniques are used to secure digital data during transmission from sender to receiver. Because digital images can be easily reproduced, cryptosystems cannot solve this problem perfectly. The second security measure that completes encryption is to attach a secret signal, a watermark, directly to the original data so that it remains available during use. Watermarking cannot prevent duplication, modification and distribution of digital media by itself, so it must be combined with cryptography. Embedding is done by modifying the average pixel intensity value of each block in the range determined by the contrast value for a particular block. This reduces the effect of modification as felt by the human eye. The extraction procedure calculates and compares the number of pixel values for blocks of the original image and watermark. The results show the robustness of the scheme towards general image processing operations such as cropping, modification, low pass filters, median pass filters, minimized and lossy JPEG compression with various quality index factors. The results also illustrate that the watermark is safe, restored and recognized even after the watermark image has been damaged, forged and modified by a general image processing operation. A comparative study of the scheme proposed with the existing scheme has also been carried out to observe the strength of the scheme.
Highlights
PENDAHULUAN Banyak vendor dan pengembang komersial menggunakan internet untuk mengirimkan data dan melakukan transaksi bisnis
The results show the robustness of the scheme towards general image processing operations such as cropping, modification, low pass filters, median pass filters, minimized and lossy Joint Photographic Experts Group (JPEG) compression with various quality index factors
Kliklah tombol „Proses‟ sehingga sistem akan menampilkan citra watermark yang terekstrak keluar, seperti terlihat pada gambar berikut: Gambar 8 Tampilan Watermark Hasil Ekstraksi
Summary
Masalah yang akan dibahas dalam penelitian ini mencakup: 1. Input program adalah citra dalam format. Penerima dari pesan itu akan melakukan otentikasi terhadap pesan itu dengan mengkomputasi nilai hash dan kemudian membandingkannya dengan nilai hash yang ada di awal pesan. 4. Dengan mengetahui nilai hash y, tidaklah bisa secara komputasi untuk menemukan x yang memenuhi H(x) = y. Pihak lawan bisa membaca pesan dan juga menghasilkan kode hash-nya. Tetapi karena pihak lawan tersebut tidak memiliki kunci untuk mendekripsikan kode hash tersebut, maka ia tidak akan bisa mengubah pesan tanpa diketahui. Hal ini sangat penting dalam digital timestamping dimana dengan menggunakan fungsi hash, seseorang dapat memperoleh dokumen dengan stempel waktu (document timestamped) tanpa menunjukkan isi dari dokumen kepada penyedia layanan timestamping. Jika pada steganografi informasi rahasia disembunyikan di dalam media digital dimana media penampung tidak berarti apa-apa, maka pada watermarking justru media digital tersebut yang akan dilindungi kepemilikannya dengan pemberian suatu informasi tertentu didalamnya
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