Both systems are public key systems, meaning that there is a secret key used for decryption and a publicly available key used for encrypting. In theory everyone can send you an encrypted message by using the public key (if they know where to obtain it), but you’re the only one who can decrypt the message. Of course these systems rely on the difficulties in obtaining the private key, when knowin...

Many cryptosystems have been released to secure electronic data on internet. Some data are very critical to be transmitted as plaintext. Thus, to ensure the data confidentiality and integrity, a list of cryptosystems have been elaborated. The most important ones are divided into two categories: symmetric algorithms encrypting and decrypting data in blocks using a single secret key; and asymmetr...

The McEliece cryptosystem is one of the oldest public-key cryptosystem ever designated. It is also the first public-key cryptosystem based on linear error-correcting codes. The main advantage of the McEliece cryptosystem is to have a very fast encryption and decryption functions but suffers from a major drawback. It requires a very large public key which makes it very difficult to use in many p...

Yuan et al. recently introduced a password-based group key transfer protocol that uses secret sharing, which they claim to be efficient and secure [9]. We remark its resemblance to the construction of Harn and Lin [1], which Nam et al. proved vulnerable to a replay attack [3]. It is straightforward that the same attack can be mount against Yuan et al.’s protocol, proving that the authors’ claim...

Randomized protocols for signing contracts, certified mail, and flipping a coin are presented. The protocols use a Z-out-of-2 oblivious transfer subprotocol which is axiomatically defined. The l-out-of-2 oblivious transfer allows one party to transfer exactly one secret, out of two recognizable secrets, to his counterpart. The first (second) secret is received with probability one half while th...

One of the key requirement of many schemes is that of random numbers. Sequence of random numbers are used at several stages of a standard cryptographic protocol. A simple example is of a Vernam cipher, where a string of random numbers is added to massage string to generate the encrypted code. It is represented as C = M ⊕ K where M is the message, K is the key and C is the ciphertext. It has bee...

We argue the necessity of universally veriiable secret sharing for secrets as individual users' cryptographic keys, and propose protocols to realize such secret sharing for two most common public-key cryptosystems: discrete logarithm based and integer factorization based. The universal veriiabil-ity achieves sharing secret with multi third parties as shareholders using two-party protocols in wh...

In 1984, Shamir [1] introduced the concept of an identity-based cryptosystem. In this system, each user needs to visit a key authentication center (KAC) and identify him self before joining a communication network. Once a user is accepted, the KAC will provide him with a secret key. In this way, if a user wants to communicate with others, he only needs to know the “identity” of his communicatio...

Multivariate Public Key Cryptosystems (MPKC) is one of candidates for post-quantum cryptography. Rainbow is an MPKC digital signature scheme, with relatively efficient encryption and decryption processes. However, the size of the secret key of Rainbow is substantially larger than that of an RSA cryptosystem for the same security level. By using sparse secret keys, the size of the secret key of ...

This paper reports security problems with improper implementations of an improved version of FEA-M (fast encryption algorithm for multimedia). It is found that an implementation-dependent differential chosen-plaintext attack or its chosenciphertext counterpart can reveal the secret key of the cryptosystem, if the involved (pseudo-)random process can be tampered (for example, through a public ti...