The attack on cryptography

Attacks against cryptography is basically solve (disassemble security) cryptographic algorithms, which are used for business data tersandi criticize without knowing / using keywords. This activity (solving cryptographic algorithms) is part of the kriptanalisis, namely the science / art tersandi solve the data. Kripanalisis and cryptography is a branch of science called kriptologi.

Data used to attack cryptographic system can be ranked as follows:

1.Only known chipertext (text passwords).

2. Plaintext (original text) and the corresponding chipertext known.

3. Plaintext selected and the corresponding chipertext.

4. Chipertext selected and the corresponding plaintext.

Method of attack

There are several methods of conducting attacks on cryptography, which is basically a method based plaintext and ciphertext based method.

1. Only the ciphertext is known: Criptanalyst (who cripanalysis) have only ciphertext have plaintext without it. Before conducting the attacks, kripanalis always make the assumption that the password algorithm used in the ciphertext is to determine the techniques solve.

Techniques used to find the plaintext / keys:

- Analisa frekuensi huruf : setiap bahasa memiliki kekhasan atas haruf-huruf yang digunakannya. Frekuensi kemunculan setiap huruf dalam suatu bahasa menjadi ciri penting yang dapat dipakai sebagai patokan untuk menganalisis plaintext/kunci suatu teks sandi. Tehnik ini umumnya digunakan untuk memecahkan metode penyandian sederhana seperti misalnya kriptografi model Caesar.

- Exhaustive attack /brute-force attack : yaitu tehnik untuk mengungkap plaintext/kunci dengan mencoba secara sistematis semua kemungkinan kunci. Walaupun tehnik ini akan berhasil menemukan plaintext/kunci, namun waktu yang dibutuhkan relatif lama dan sangat bergantung kepada kecepatan mesin (komputer) yang melakukan serangan ini. Tabel berikut memperlihatkan waktu yang dibutuhkan untuk exhaustive key search :

Size key	The number of possible keys	Time to 106 per second trial	Time to 1012 per second trial
16 bit	216 = 65536	32.7 milliseconds	0.0327microsecond
32 bit	232 = 4.3 ´ 109	35.8 minutes	2.15 milliseconds
56 bit	256 = 7.2 ´ 1016	1142 years	10.01 hours
128 bit	2128 = 4.3 ´ 1038	5.4 ´ 1024 years	5.4 ´ 1018 years

(source: William Stallings, Data and Computer Communication Fourth Edition)

-Analytical Attack: namely techniques to solve the text password to do with the weakness of the analysis algorithm kriptografinya to reduce the likelihood that the key is not there (not shown).

Carried out by solving the equation, the math equation (derived from the definition of a cryptographic algorithms), which contains changes which represents the plaintext or keywords.

By combining the analytical method and exhaustive Attack Attack will accelerate to found plaintext / key.

2. Ciphertext selected: Cripanalyst choose ciphertext, and then through the ciphertext is trying to get the plaintext appropriate. Usually done to attack public-key cryptography system.

3. Plaintext and the ciphertext is known: Kripanalis have both plaintext and ciphertext it and try to find the relationship between them. Usually done to find the keys and algorithms code that will be useful for solving the message code next.

Some messages are usually found raw format (template) that is structured. The raw format is a rift that opened opportunities for conjecture ciphertext from the nature of the plaintext. For example:

From, To, Subject, in an e-mail

With respect, respectfully, best regards, the official letter.

#include, program, go, in a source code

4. Plaintext selected: plaintext selecting Kriptanalis particular, the plaintexts that lead to more discoveries key to encrypted and learn / compare results password (ciphertext). Usually this is used to solve the password in asymmetric encoding method, which kripanalis usually have a public-key it.

Illustrated in the picture: (picture taken from the internet)

5.Ciphertext or known plaintext in Adaptive: Kriptanalis block of plaintext selecting a large or ciphertext, and disandi, and then select the block other smaller based on the results of previous attacks, so the next.

6.Key selected: Kriptanalis have knowledge about the relationship between the keys of a different, and then choose the right key to open the message code. Usually used to know the algorithm encoded a message.

7. Social engineering / rubber-hose cryptanalysis: Looking for information algorithms / password by key intelligence activities, threatening, send a letter of dark, rack (black-mail) or kidnapping / torture to those who hold the key to give the key to open the message.

Types of Seizures

Based on the involvement of the attacker in the conduct of activities:

1. Attack passive (passive Attack): attacker is not involved in the communication between the sender and recipient, the attacker only tapping to obtain data or information as much as possible

Methods used in tapping this usually do wiretapping, electromagnetic eavesdropping or acoustic eavesdropping

2. Attack on (the active Attack): attacker mengintervensi communication and to influence the system to benefit himself. Striker change the flow of messages, such as removing some of ciphertext, the ciphertext, insert a snippet of ciphertext false, me replay the message a long time, change the stored information, etc.

Methods used :

Man-in-the-middle-Attack: Striker seems to acknowledge as the party entitled to receive a message on the message sent. Or the attacker to act as though as the original message.

A user sends a message m in AGENDA 1234qw with the public key to user B, but in the transmission cut / taken by the man-in-the-middle-Attack (mitma). Then change the message mitma m in AGENDA KKK with a public key to the user ASD123 B. User B KKK receive messages sent by the presumed user A.

Illustrated in the picture: (picture taken from the internet)

Knowledge of the attacks against cryptography is very important to improve the effectiveness and quality of the encoding algorithm is used. Principles that are used in determining the use of a cryptographic algorithms are:

1. Mathematical equation that describes the operation of cryptographic algorithms that are made extremely complex so that the algorithm may not be solved by analytical or

2. Cost to solve ciphertext exceeds the value of the information contained in the ciphertext; or

3. Time needed to solve the ciphertext exceeds the length of time the information must be kept confidential.

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