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Serangan Terhadap Skema Enkripsi Winzip Menggunakan Known

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Serangan Terhadap Skema Enkripsi Winzip Menggunakan Known Skema Enkripsi Pada WinZip dan Serangannya Andresta RamadhanSetiawan (13503030) Program Studi Teknik Informatika Sekolah Teknik Elektro dan Informatika, Institut Teknologi Bandung Jl. Ganesha 10 Bandung Email : [email protected] Abstrak Winzip merupakan aplikasi kompresi yang sangat popular pada system operasi Windows. Selain melakukan kompresi, untuk menjaga kerahasiaan arsip, Winzip menyediakan fitur enkripsi. Versi terbaru yang ada di situs resminya yaitu Winzip 10 menggunakan enkripsi AES untuk melindungi arsip rahasia pengguna. Untuk mendukung enkripsi pada versi Winzip yang lama (sebelum versi 9), pada versi terbaru ini juga masih disertakan enkripsi tradisional ZIP 2.0. Pada makalah ini akan dijelaskan bagaimana mengenai format berkas zip, bagaimana skema enkripsi yang digunakan oelh WinZip untuk melindungi berkas-berkas rahasia. Skema Enkripsi WinZip rentan terhadap serangan seperti known- plaintext attack, random seed attack. Serangan menggunakan bruteforce atau dictionary attack juga cukup berbahaya jika password yang digunakan pendek, dalam waktu yang singkat password dapat diperoleh. Hal ini yang biasanya digunakan program password recovery untuk mendapatkan password. Kata Kunci : WinZIP, Known Plaintext Attack, plaintext, chipertext. 1. Pendahuluan menjadi berkas zip telah terkompresi sehingga lebih kecil ukurannya dari berkas aslinya. ZIP format adalah salat satu dari sekian banyak format yang paling banyak digunakan oleh Penghematan ruang penyimpanan. Seperti telah program kompresi dan pengarsipan data pada disebutkan, berkas yang diarsipkan menjadi berbagai macam sistem operasi. Satu atau lebih berkas zip akan dikompresi sehingga ukurannya berkas (file) yang telah dikompres dapat dimuat lebih kecil. Hal ini bermanfaat untuk menghemat pada satu berkas zip (zip file). Zip file menjaga ruang penyimpanan pada diska. Jika anda berkas-berkas yang saling berhubungan tetap memiliki berkas yang berukuran besar dan jarang menyatu sehingga akan mudah untuk digunakan arsipkan saja menjadi berkas zip dan disebarluaskan baik itu lewat email, mengunduh unzip hanya jika berkas tersebut akan digunakan. berkas dari internet selain itu kemampuannya untuk mengkompresi data membuat penyimpanan Menjaga berkas sekelompok berkas tetap utuh. berkas zip lebih efisien. Berikut ini adalah Ketika mengirimkan berkas-berkas dalam satu beberapa keuntungan menyimpan berkas dalam berkas zip tentunya akan lebih menguntungkan, format zip karena kemungkinan berkas 'tercecer' atau hilang sangat kecil. Memudahkan pendistribusian data lewat internet. Pendistribuasian data lewat internet akan lebih 2. Berkas .ZIP mudah dan cepat, terutama data yang terdiri lebih dari satu arsip. Hanya dengan unduh untuk Sejarah mengambil satu atau lebih berkas yang Berkas format ZIP diciptakan oleh Phil Katz, dibutuhkan selain itu prosesnya pun akan lebih pendiri PKWARE, setelah perselisihan mengenai cepat karena semua berkas yang diarsipkan hak paten merek dagang ARC (kependekan dari archieve) dan ekstensi nama berkas .arc antara 1 PKWare dengan System Enhancement Associates ZIP semakin dikenal dan digemari sehingga dapat (SCA). dikatakan ZIP telah menjadi standar untuk kompresi dan pengarsipan berkas. Hampir semua Produk pengarsipan PKWare yang pertama program pengarsipan dan kompresi berkas saat adalah PKARC menggunakan kode sumber yang ini mendukung format ZIP. Salah satu program dipublikasikan oleh SCA. Kode sumber SCA dari sekian banyak yang ada dan banyak yang ditulis dalam bahasa C diubah digunakan, dan yang akan dibahas dalam menggunakan bahasa asembly (mesin) sehingga makalah ini, adalah WinZip. lebih cepat prosesnya. PKArc juga menggunakan ekstensi nama berkas yang sama dengan yang Informasi Teknis digunakan SCA yaitu ".arc". Oleh karean itu, Spesifakasi format ZIP mengindikasikan bahwa SCA menuntut royalti atas penggunaan merek berkas-berkas dapat disimpan tanpa kompresi dagang dan kode sumbernya. Akan tetapi atau dengan menggunakan variasi alogoritma PKWare menolak. SCA memenangkan tuntutan kompresi lainnya. Pada kenyetaannya, format ZIP di pengadilan atas pelanggaran merek dagang yang digunakan menggunakan algoritma oleh PKWare. Akhirnya Katz merilis ulang DEFLATEnya Katz, kecuali ketika berkas yang produknya dengan mengganti nama menjadi ditambahkan pada arsip telah dikompresi terlebih PKPAK. dahulu atau berkas tersebut akan rusak jika dikompresi. Walaupun sudah mengganti nama menjadi PKPAK, Katz tetap harus membayar lisensi atas Untuk masalah keamanan berkas yang peggunaan kode sumber SEA. Karena Katz tetap diarsipkan, ZIP mendukung penggunaan kata menolak untuk membayar royalti akhirnya ia sandi untuk mengenkripsi menggunakan enkripsi membuat format berkas pengarsipan sendiri, yang kunci simetri. Beberapa fitur baru ditambahkan sampai sekarang terkenal diseluruh dunia sebagai seperti metode enkripsi dan kompresi yang lebih format ZIP. Format ZIP yang didesain Katz lebih mutahir. Tapi fitur ini tidak didukung oleh semua kokoh dan tahan terhadap korupsi data dari pada program pengarsipan dan kompresi yang ada format ARC karena katolag data yang dipasaran. Salah satu program yang mendukung "redundan". Selain itu, ZIP juga lebih fleksibel enkripsi adalah WinZip, yang akan dibahasah karena memungkinkan adanya tambahan pada makalah ini. algoritma untuk kompresi data dan juga tempat unuk pengembangan lebih jauh. Ketika perangkat lunak PKZIP dirilis, banyak orang yang mulai 3. WinZip meninggalkan format ARC karena dinilai lebih lambat dan tidak efektif performanya dalam WinZip adalah sebuah program pengarsipan dan melakukan kompresi data. kompresi berkas yang cukup banyak digunakan dan berjalan pada sistem operasi Windows. Katz mempublikasikan dokumen teknis format Dikembangkan oleh WinZip Computing, dulunya berkas ZIP bersamaan dengan dikeluarkannya Nico Mak Computing, WinZip menggunakan versi pertama perangkat lunak pengarsipan format PKZIPnya PKWARE dengan dukungan PKZIP pada bulan Januari 1989. Penggunaan tambahan terhadap format kompresi lainnya. nama ZIP (yang berarti cepat) diusulkan oleh Robert Mahoney. Mereka menginginkan WinZip mulai memasarkan produknya pada produknya lebih cepat dari pada ARC dan format tahun 1990an sebagai antarmuka grafis untuk kompresi yang lainnya. PKZIP. Pada sekitar tahun 1996, pencipta WinZip menggabungkan kode kompresi yang Ketika antarmuka berbasis grafis (graphical user berasal dari proyek Info-ZIP, kemudian interface) mulai banyak digunakan pada sistem menghilangkan kebutuhan akan eksekusi PKZIP operasi, mulai banyak program kompresi dan untuk disertakan pada produk WinZip. Pada pengarsipan bebasi grafis. Kebanyakan program- tanggal 2 Mei 2006, Corel Corporation program tersebut menggunakan format ZIP. Pada mengakuisisi WinZip Computing. akhir tahun 1990 telah banyak aplikasi pengaturan berkas (file manager) yang Yang membuat WinZip banyak digunakan orang mengintegrasikan format ZIP bahkan Microsoft adalah karena fitur-fitur yang ditawarkannya, bahkan mengintegrasikan format ZIP pada sistem antara lain: operasi Windowsnya. Hal ini membuat format 2 - mengkompresi dan melakukan berdasarkan standar keamanan saat ini sehingga "unzipping" format arsip PKZIP. penggunaannya hanya untuk keperluan keamanan - integrasi terhadap shell Windows yang rendah, tidak direkomendasikan untuk - mengenkripsi berkas rahasia menggunakan melakukan enkripsi pada berkas yang sangat enkripsi kunci simetri rahasia. Alasan enkripsi ZIP 2.0 ini masih - menulis arsip ZIP langsung ke CD maupun disertakan adalah untuk mendukung DVD kompatibilitas terhadap aplikasi ZIP yang dahulu - versi 9.0 mengimplementasikan format yang mungkin masih digunakan sampai saat ini. PKZIP versi 64-bit yang mendukung lebih dari 65.535 berkas dalam satu arsip zip Proses enkripsi dilakukan pada aliran data yang dan ukuran arsip ZIP yang lebih dari 4 telah terkompresi. Berkas yang terenkripsi harus Gigabyte didekripsi terlebih dahulu sebelum diekstraksi - versi 10.0 mendukung bzip2 dan algoritma menjadi berkas-berkas asli. kompresi PPMd yang menghasilkan berkas arsip yang lebih kecil. Setiap berkas yang dienkripsi memiliki 12 byte - dapat bekerja dengan arsip ARC, ARJ, dan tambahan yang disimpan pada awal area data LHA. yang isinya mendefinisikan "header" enkripsi - mendukung format kompresi TAR, Z, GZ, untuk berkas tersebut. Header enkripsi tersenbut TAZ, dan TGZ yang biasa digunakan pada diisi dengan bilangan acak (random) dan lingkungan UNIX. kemudian dienkripsi menggunakan 3 buah kunci masing-masing 32-bit. Ketiga kunci tersebut Dari fitur-fitur diatas, yang menjadi sorotan diinisialisasi oleh kata kunci yang diisikan. adalah masalah keamanan yang ditawarkan oleh Setelah tiap byte data dienkripsi, kunci-kunci WinZip. Enkripsi yang disediakan WinZip harus tersebut kemudian diperbarui menggunakan dapat menjamin pengguna yang memiliki kunci teknik pembangkitan bilangan pseudo-random saja yang dapat mengakses berkas ZIP yang telah yang dikombinasikan dengan algoritma CRC-32 dienkripsi. Berikut ini adalah langkah-langkah secara umum Winzip untuk versi 9.0 keatas mendukung 128 yang dilakukan untuk mendekripsi berkas ZIP : dan 256 bit kunci enkripsi AES yang tentunya 1. Inisialisasi tiga buah kunci 32-bit dengan menyediakan tingkat keamanan yang lebih kata kunci. dibandingkan metode enkripsi Zip 2.0 yang 2. Baca dan dekripsi 12 byte header enkripsi, digunakan pada WinZip sebelum versi 9.0. AES kemudian inisialisasi kunci enkripsi enkripsi pada WinZip yang telah disertifikasi 3. Baca dan dekripsi aliran data yang FIPS-197 menggunakan algoritma kriptografi terkompres
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