A5/3 is a stream cipher used for encrypting data in mobile communications, particularly in the GSM (Global System for Mobile Communications) standard. It was developed to enhance the security of voice and data transmissions over mobile networks. A5/3 is based on the KASUMI algorithm, which is a block cipher that provides a higher level of security compared to its predecessor, A5/1. The A5/3 encryption method uses a key length of 128 bits, making it more resistant to attacks than earlier algorithms. It operates by generating a keystream that is combined with the plaintext data to produce ciphertext. This process ensures that sensitive information remains confidential during transmission, protecting users from eavesdropping and unauthorized access.