Efficient transmission of cryptographic information in secure real time protocol. A transmitting terminal may be used to encrypt data with a session key derived from a bit-stream. The bit-stream may be sent with header information to the receiving terminal. To conserve bandwidth, the information may be divided into portions, and each portion transmitted with an encrypted data packet. The receiving terminal may be used to recover the bit-stream from the information portions in the packet headers, and use the bit-stream to derive the session key. The session key may be used to decrypt the data.