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Thread: About Block Ciphers or Types of Encryption

  1. #1
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    About Block Ciphers or Types of Encryption

    Rather than using keys such as huge as a digit disposable, is used more often algorithms that have a secret key relatively small (80 to 128 bits, but using this key to a seemingly complex it is impossible for an enemy to find the value.

    Therefore, since the key is so small, it is not easy to try all possibilities to reach the decryption? In fact, no computer could be achieved in a realistic timeframe. Indeed, if the key was 128 bits, ie a sequence of 128 "0" and "1", there would be 2128 or 100000000000000000000000000000000000000 possible keys!

    The objective is to: develop from a random message M numbers, or at least that seems random, only the detention of the key K to decrypt.
    Specifically, it involves constructing a bijective function "pseudo-random":
    • It must be a bijection, since it must correspond to each digit of the plaintext message a number of coded message, and because it must allow power from a number C, trace uniquely corresponds to the message plain
    • It must be random or appear: in cryptography, perfection is random, the coded message is appearing to arise directly from the chance to reduce the risk of an attack by analyzing the ciphertext, its redundancy, etc..


    The development of a function involving these two conditions posed a problem for cryptographers until the 1950s when Feistel showed a pseudo-random function is transformed by a simple method, bijection. Currently, the method of secret-key encryption used more frequently.


    Explanation:
    1. Let a function f that takes as argument a word of n bits.
    2. The encryption algorithm will proceed by encrypting blocks of 2n bits, which divides into 2 parts of n bits each: the parties (L) and right (D).
    3. The image of the block (G, D) is the block (L, R) with L and R D = G = XOR f (D).
    4. This transformation is bijective, because if we have a couple (L, R), there are many (G, D) with D = L and G = R XOR F (L).
    5. The right side has not been processed (sent just to the left). It must therefore repeat the Feistel scheme a number of times (known as rounds).

  2. #2
    Join Date
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    Re: About Block Ciphers or Types of Encryption

    Encryption are basically of two types named as Symmetric encryption & Asymmetric encryption.

    1. The encryption technique called "symmetric" (or "private-key") is based on the fundamental notion of key (information to encrypt / decrypt a message): indeed, in this type of encryption, security of communication data depends entirely on her.

    The principle: Alice wants to send confidential data to Bob, they both have an identical key. Alice encrypts the message and sends it to Bob who decrypts it using the same key.

    Features: Using a single key to encrypt and decrypt.

    Symmetric encryption is divided into two systems:

    Stream cipher : This system encrypts data one bit regardless of the length of the message to be encoded without the need for cutting. The stream cipher algorithms (or "in flow") can be treated as block ciphers, where the block has a unit size (eg 1 bit). The main advantage of this method is its high speed to transmit data, in addition to the fact that this technique allowed the propagation of errors. Another positive point is that you can use with devices with low memory.

    Examples:

    -Algorithm A5: In GSM, it is used to encrypt radio communications between the phone and relay antenna closest;

    - RC4 Algorithm: used by WEP (Wired Equivalent Privacy) for securing wireless networks like Wi-Fi has become especially vulnerable following the discovery of weaknesses allowing breaking Wi-Fi transmission WEP in seconds. That's why he was replaced by the RC5, incomparably stronger.

    Block cipher : This system cuts the data into blocks of same size and then encrypts them one after the other. The size of these blocks is essential for the security of communication by cons, large blocks are safer but also more cumbersome to move.

    Example:

    - AES (Advanced Encryption Standard or "Advanced Encryption Standard") encryption standard currently approved by the U.S. Department of Commerce.

  3. #3
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    Re: About Block Ciphers or Types of Encryption

    The basis of cryptography called "asymmetric" or "public key" is the existence of one-way functions are easy to apply to a message, but makes return to this original message extremely complex from the time or function of this type was applied. In fact, this technique uses cryptographic functions not only one way but also to break secret: these functions are, as explained above, very difficult to reverse, unless you have very precise information, a private key (secret).

    The principle: Alice wants to receive encrypted messages to anyone, here we will talk more specifically Bob. Alice then generates two keys: it sends the first (public) to Bob and keeps secret the second (closed). With the key given by Alice, Bob encrypts the message and then sends him: it decrypts said message using its private key. To better understand: Analogy of the safe. (The public key, as the address on an envelope, allows anyone to send encrypted messages, but only the recipient can open the box, that holds the private key to decrypt.)

    Encryption: Alice chose a safe. It sends open to Bob, and keeps the key. When Bob wants to send a message to Alice, he leaves his message, closes the trunk, and returns to Alice. Upon receipt, only Alice can open the trunk, since it alone possesses the key, assuming the trunk inviolable, and nobody can find the key.

    Authentication or signature: Alice places a message in the safe before it closes to send it to Bob. If Bob comes to using the public key of Alice that he has to open the safe is that it is that Alice and therefore it is she who has placed the message.

    Features:
    - The existence of two different keys to encrypt and decrypt;
    - The fact that the key figure is public.

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