The present invention is a data processing apparatus and method for encrypting, sending, receiving, and decrypting secure transmissions using a cellular telephone. The user may either purchase a cellular telephone which contains the encryption and decryption software, download the encryption and decryption software to an existing cellular telephone, or may purchase an encryption component which is adaptable to a conventional cellular telephone. Additionally, the described system of encryption and decryption can be used for secure communications in PDA/cellular telephones combinations and any other type of portable communications device.The encryption process is a Java application which converts the user's audio signal into a wav file. The encryption program then creates a second wav file using the first wav file header. The encryption program then converts the data in the first wav file into encrypted data in the second wav file using public key encryption and a series of data manipulations. The encrypted second wav file is then transmitted to the intended recipient. Only recipients with the corresponding private key which matches the public key used to encrypt the data will be able to decrypt the transmitted data.In the decryption process, the user receives a wav file transmitted from the sender. The decryption program then decrypts the encrypted wav file using public key encryption and a series of data manipulations. The decryption program then converts the encrypted data in the first wav file into decrypted data in the second wav file using public key encryption and a series of data manipulations. The decrypted second wav file is then emitted over a speaker to the intended recipient.