Category Archives: Types

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.


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.


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.