Category Archives: Types


Symmetric Key Cryptography

Symmetric Key Cryptography refers to encryption methods in which both the sender and receiver share the same key.  This was the only kind of encryption publicly known until June 1976. Since then other schemes have also emerged on the scene, however, Symmetric Key Cryptography is still one of the most well researched area of this field.   

Symmetric key ciphers are implemented as either block

ciphers or stream ciphers. A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a stream cipher.

The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are block cipher designs which have been designated cryptography standards by the US government cialis paiement paypal (though DES’s designation was finally withdrawn after the AES was adopted). Despite its deprecation as an official standard, DES (especially its still-approved and much more secure triple-DES variant) remains quite popular; it is used across a wide range of applications, from

ATM encryption to e-mail privacy and secure remote accessStream ciphers, in contrast to the ‘block’ type, create an arbitrarily long stream of key material, which is combined with the plaintext bit-by-bit or character-by-character, somewhat like the one-time pad. In a stream cipher, the levitra bayer uk cheap output stream is created based on a hidden internal state which changes as the cipher operates. That internal state is initially set up using the secret key material. RC4 is a widely used stream cipher. 


CRG, the cryptanalysis of block and stream ciphers is actively being researched by the group members. In addition, the group is also working on the design and analysis of boolean functions.

Information Security

Public Key Cryptography

Symmetric-key cryptosystems order levitra generic use the same key

for encryption and decryption of a message, though a message or group of messages may have a different key than others. A significant disadvantage of symmetric ciphers is the key management necessary to use them securely. Each distinct pair of communicating parties must, ideally, share a different key, and perhaps viagra naturel maca each ciphertext exchanged as well. The number of keys required increases as the square of the number of network members, which very quickly requires complex key management schemes to keep them all consistent and secret. The difficulty of securely establishing a secret key between two communicating parties, when a secure channel does not already exist between them, also presents a chicken-and-egg problem which is a considerable practical obstacle for cryptography users in the real world.

In a groundbreaking 1976 paper, Whitfield Diffie and Martin Hellman proposed the notion of public-key (also, more generally, called asymmetric key) cryptography in which two different

but mathematically related keys are used—a public key and a private key. A public key system is so constructed that calculation of one key (the ‘private key’) is

computationally infeasible from the other (the ‘public key’), tadalafil vasodilator even though they are necessarily related. Instead, both keys are generated secretly, as an interrelated pair. The historian David Kahn described public-key cryptography as “the most revolutionary new concept in the

field since polyalphabetic substitution emerged

in the Renaissance”.

At CRG, interesting areas of this field including signcryption, identity based encryption, digital signatures and elliptic curve cryptography are currently being researched by the group members.



The goal of cryptanalysis is to find some weakness or insecurity in a cryptographic scheme, thus permitting its subversion or evasion.

There are a wide variety of cryptanalytic attacks, and they can be classified in any of several ways. A common distinction turns on what an attacker knows and what capabilities are available. In a ciphertext-only attack, the cryptanalyst has access

only to the ciphertext (good modern cryptosystems are usually effectively immune to ciphertext-only attacks). In a known-plaintext attack, the

cryptanalyst has access to a ciphertext and its corresponding plaintext (or to riesgos del consumo de viagra many such pairs). In a chosen-plaintext attack, the cryptanalyst may commander viagra pas cher choose a plaintext and learn its corresponding ciphertext (perhaps many times) and in a chosen-ciphertext attack, the cryptanalyst may be able to choose ciphertexts and

learn their corresponding plaintexts. Also important, often overwhelmingly so, are mistakes generally in the

design or use of one of the protocols involved.

At CRG, the group members are working on the cryptanalysis of a number of widely known symmetric and asymmetric ciphers.


Cryptographic Hash Functions

A cryptographic hash function is a hash function which is considered practically impossible to invert, that is, to recreate the input data from its hash value alone. The input data is often called the message, and the hash value is often called the message digest or simply the digest.

The ideal cryptographic hash function has four main properties:

  • it is easy to compute the hash value for any given message
  • it is infeasible to generate a message that has a given hash
  • it is infeasible to modify a message without changing the hash
  • it is infeasible to find two different messages with the same hash

Cryptographic hash functions have

many information security applications, notably in digital signaturesmessage authentication codes (MACs), and other forms of authentication. They can also be used as ordinary hash functions, to index data in hash tables, for fingerprinting, to detect duplicate data or uniquely identify files, and

as checksums to detect accidental data corruption. Indeed, in information security contexts, cryptographic

hash values are sometimes called (digitalfingerprintschecksums, or just hash values.

At CRG, research on time complexity of hash functions and use of hash functions for compression is being conducted by the group members.


Quantum Cryptography

Quantum cryptography describes the

use acheter viagra of quantum mechanical effects (in particular quantum communication and quantum computation) to perform cryptographic tasks or to break cryptographic systems.

Well-known examples of quantum cryptography are the use of quantum communication to exchange a key securely (quantum key distribution) and the hypothetical use of quantum computers that would allow the breaking of various popular public-key encryption and signature schemes (e.g. RSA and ElGamal).

The advantage of quantum cryptography lies in the fact that it allows the completion of various cryptographic tasks that are

proven or conjectured to be impossible using only classical (i.e. non-quantum) communication.

The most well known and developed application of quantum cryptography is quantum key distribution (QKD). QKD describes the process of using quantum communication to establish a shared key between two parties (usually called Alice and Bob) without a third party (Eve) learning anything about that key, even if Eve can eavesdrop on all communication between Alice and Bob. This is achieved by Alice encoding

the bits of

the key as quantum data and sending them to Bob; if Eve tries to learn these bits, the messages will be disturbed and Alice and Bob will notice. The key is then typically used for encrypted communication.

At CRG, group members are currently researching on quantum key distribution and role of quantum cryptography in noise reduction.


Zero Knowledge Proofs

A protocol between two parties Alice and Bob is zero-knowledge (from Alice’s point of view), if it does not leak any information to Bob. Zero-knowledge is a viagra naturel maca fundamental notion in cryptography and has important applications. For example, Alice can prove to Bob that she knows a secret key corresponding to a given public key (e.g., for identifying herself to Bob) without leaking any information whatsoever about the secret key.

A zero-knowledge proof must satisfy three properties:

  1. Completeness: if the statement is true, the honest verifier (that is, one following the protocol properly) will be convinced of this fact by an honest prover.
  2. Soundness: if the statement viagra feminin forum uso is false, no cheating prover can convince the honest verifier that

    it is true, except with female viagra some small probability.

  3. Zero-knowledge: if the cialis generique statement is true, no cheating verifier learns anything other than this fact. This is formalized by showing that every cheating verifier has somesimulator that, given only the statement to be proved (and no access to the prover), can produce a transcript that “looks like” an interaction between the honest prover and the cheating verifier.

The first two of these are properties of more general interactive proof systems. The third is what makes the proof zero-knowledge.

At CRG, researchers are currently working on finding feasible solutions for using zero knowledge proofs

for authentication and access control.