Kriptografi (Penyandian Data)

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Posted by edy winarno on October 1, 2009 at 3:06 am

Ilmu kriptografi adalah ilmu yang mempelajari tentang penyembunyian huruf atau tulisan sehingga membuat tulisan tersebut tidak dapat dibaca oleh orang yang tidak berkepentingan. Kriptografi sudah dipakai sejak jaman Julius Caesar dimana akan mengirimkan pesan kepada panglimanya tetapi tidak mempercayai kurir pembawa pesan tersebut. Kriptografi mempunyai 2 (dua) bagian yang penting, yaitu enkripsi dan dekripsi. Enkripsi adalah proses dari penyandian pesan asli menjadi pesan yang tidak dapat diartikan seperti aslinya.
Dekripsi sendiri berarti merubah pesan yang sudah disandikan menjadi pesan aslinya. Pesan asli biasanya disebut plaintext, sedangkan pesan yang sudah disandikan disebut ciphertext. Pada Gambar 1 dapat dilihat bahwa masukan berupa plaintext akan masuk ke dalam blok enkripsi dan keluarannya akan berupa ciphertext, kemudian ciphertext akan masuk ke dalam blok dekripsi dan keluarannya akan kembali menjadi plaintext semula.
kripto1
Gambar 1. Proses Enkripsi dan Dekripsi

Ada 2 (dua) model algoritma enkripsi yang menggunakan kunci, yaitu kunci simetrik dan kunci asimetrik. Enkripsi kunci simetrik yang biasanya disebut enkripsi konvensional adalah enkripsi yang menggunakan kunci yang sama untuk enkripsi maupun dekripsi, dari Gambar 2 terlihat bahwa untuk mengenkripsi maupun mendekripsi pesan hanya menggunakan satu buah kunci (K) saja.
kripto2

Gambar 2. Enkripsi-dekripsi Kunci Simetrik

Penggunaan metode ini membutuhkan persetujuan antara pengirim dan penerima tentang kunci sebelum mereka saling mengirim pesan. Keamanan dari kunci simetrik tergantung pada kerahasiaan kunci, apabila seorang penyusup dapat menemukan kunci maka dengan mudah dapat membaca pesan yang sudah dienkripsi. Enkripsi kunci simetrik dapat dibagi kedalam 2 (dua) kelompok yaitu metode stream cipher dan metode block cipher.

Enkripsi kunci asimetrik (biasa disebut enkripsi kunci publik) dibuat sedemikian rupa sehingga kunci yang dipakai untuk enkripsi berbeda dengan kunci yang dipakai untuk dekripsi. Enkripsi kunci publik disebut demikian karena kunci untuk enkripsi boleh disebarluaskan kepada umum sedangkan kunci untuk mendekripsi hanya disimpan oleh orang yang bersangkutan. Enkripsi asimetrik dapat ditulis seperti berikut:
Ek (P) = C Dk (C) = P
Contohnya seperti pada Gambar 3 bila seseorang ingin mengirim pesan kepada orang lain maka orang tersebut menggunakan kunci publik orang tersebut untuk mengenkripsi pesan yang kita kirim kepadanya lalu orang tersebut akan mendekripsi pesan tersebut dengan kunci privat miliknya.
kripto3
Gambar 3. Enkripsi Kunci Asimetrik

Tujuan Dari Kriptografi

Seperti juga perkembangan ilmu kriptografi, tujuan-tujuan dari kriptografi teruslah berkembang. Bila pertama kali dibuat hanya untuk keamanan data saja, tetapi sekarang semakin banyak tujuan-tujuan yang ingin dicapai, yaitu:
1. Privasi, Musuh tidak dapat membongkar tulisan yang kita kirim.

2. Autentikasi, Penerima pesan dapat meyakinkan dirinya bahwa pesan yang diterima tidak terjadi perubahan dan berasal dari orang yang diinginkan.
3. Tanda tangan, penerima pesan dapat meyakinkan pihak ketiga bahwa pesan yang diterima berasal dari orang yang diinginkan.
4. Minimal, Tidak ada yang dapat berkomunikasi dengan pihak lain kecuali berkomunikasi dengan pihak yang diinginkan.
5. Pertukaran bersama, suatu nilai (misalnya tanda tangan sebuah kontrak) tidak akan dikeluarkan sebelum nilai lainnya (misalnya tanda tangan pihak lain) diterima.
6. Koordinasi, di dalam komunikasi dengan banyak pihak, setiap pihak dapat berkoordinasi untuk tujuan yang sama walaupun terdapat kehadiran musuh.

Untuk membahas lebih lanjut akan saya sajikan beberapa tulisan saya yang lain tentang kriptografi.(winarnoedy@gmail.com owner of edywinarno.com)

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Filed under Dunia Komputer, Pemrograman, kriptografi

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On April 8, 2010 at 7:52 am twilight eclipse said

hi terrific little website you got there I utilize the same exact template on mine yet unfortunately for what ever reason it looks to stream better on this web site eventhough the one you have is carrying more multimedia. Have you been using any individual plug ins or widgets that will speed it up? If you could give the names so that I might use these on my blog so twilight breaking dawn fans could watch twilight breaking dawn online trailers and videos more quickly I’d personally always be pleased – kudos ahead of time
On May 7, 2010 at 10:35 am seolace said

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On May 9, 2010 at 11:58 am indian videos said

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On May 10, 2010 at 2:18 am horse breeding videos said

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On June 7, 2010 at 5:22 am Robert Pattinson said

hey i submitted a comment a while back on the subject of exactly how to speed up my twilight eclipse site’s load time seeing as we used the very same theme back then and someone placed a remark answering it on my website a week ago – if that was you I just wanted to say hi and thanks, and if it wasn’t you then i’m sorry to bother you, but thanks anyhow!
On June 10, 2010 at 1:58 pm Juliette Blomberg said

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On September 27, 2011 at 7:32 pm Terina Manwill said

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On October 1, 2011 at 10:24 pm Polycom said

I’ve been reading your entries during my morning holiday, and I will have to admit the whole article has been very enlightening and really well written. I assumed I’d assist you to recognise that for some reason this blog does now not view neatly in Web Explorer 8. I wish Microsoft could forestall changing their software. I’ve a question for you. Would you thoughts exchanging blog roll links? That may be truly neat!
On October 2, 2011 at 1:12 am bhj4333tylf7 mae said

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On October 2, 2011 at 5:57 pm XXX Videos said

Sorry for the huge review, but I’m really loving the new Zune, and hope this, as well as the excellent reviews some other people have written, will help you decide if it’s the right choice for you.
On October 4, 2011 at 5:39 am Theo Trimarchi said

I like the valuable info you provide in your articles. I’ll bookmark your weblog and check again here regularly. I am quite certain I will learn lots of new stuff right here! Best of luck for the next!
On October 4, 2011 at 5:49 pm Genoveva Harriss said

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On October 4, 2011 at 11:17 pm what is the best franchise to own said

yours and my visitors would genuinely benefit from a lot of the information you present here. Please let me know if this alright with you. Regards!
On October 6, 2011 at 7:26 am online free casino said

BigBadJohnNow youre talking!! Both parties stink.
On October 7, 2011 at 12:51 am transexuel said

Apple now has Rhapsody as an app, which is a great start, but it is currently hampered by the inability to store locally on your iPod, and has a dismal 64kbps bit rate. If this changes, then it will somewhat negate this advantage for the Zune, but the 10 songs per month will still be a big plus in Zune Pass’ favor.
On October 7, 2011 at 9:35 am Best Movies Ever said

Ive heard similar tales of the value of vintage Cambodian breweriana. For example, these Beer Lao and Angkor coasters on sale for an opening price of GBP4.95.
On October 8, 2011 at 9:17 am www.chase.com said

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On October 8, 2011 at 11:53 pm top 100 franchise opportunities said

In total, it took me approximately 20 minutes to discover this fantastic post. Thanks a lot.
On October 9, 2011 at 11:10 am Los Angeles answering service said

I genuinely adore your weblog. It looks terrific and you give great information and facts too!
On October 9, 2011 at 6:10 pm Randolph Ferbrache said

It’s hard to search out educated people on this topic, but you sound like you know what you’re talking about! Thanks
On October 10, 2011 at 5:24 am Blythe Blaker said

I warned people I know what would happen if Obama was elected. You get to know someone by the people they consider friends and with whom they associate. Obama lied about so much during the campaign. I dont see the charisma or the great speech making ability. I see someone whose smile reminds me of the crocodile in the movie Peter Pan. I saw vibes coming from him that made my skin crawl. His voice gives me chills. They say hes brilliant, but the only brilliane I see is coopting someone elses ideas. I had Clinton pegged as the lech he is the first time I saw his face and heard him speak on TV. Too many people voted for Obama because of his skin color and that his election made history. I see someone that made history as the first Communist elected as our president. What is happening now almost makes me cry for the future generations of this country. I fear for my grandchildren and great grandchildren.
On October 10, 2011 at 6:13 am izolacja fundamentów said

Poradnik tworzony na bieżąco z myślą o osobach remontujących istniejące domy lub budująchych całkiem nowe obiekty. Z łatwością znajdziesz tu odpowiedzi na kwestie dotyczące twojego projektu. Dzięki naszym artykułom unikniesz niepotrzebnych rozczarowań i kosztów.

Kriptografi (Penyandian Data)

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