There is a need for high security of information in financial transactions. This security is assured using various encryption algorithms such as RSA, DES, AES, and, in last time, with hybrid encryption algorithms. The problem arises when financial transactions take place in the banking sector involving large amount of data, involving the need for very fast, even real-time, and strong secured encryption, transmission and decryption algorithms. In this paper we proposed a new cryptography system for sensitive financial (bank or stock exchange) data that uses a combination of logistic map and sigmoid function for generating a secret key and a version of ElGamal cryptosystem based on elliptic curves for the transfer of the secret key online. This approach assures higher efficiencies in term of fast and strongly secured performance.