2. SAFETALK Jodie Au Josh Chong Tam Paredes Jeff Sieben Amelia Yeoh

3. Introduction n n Complete system designed to provide security from eavesdropping devices over a telephone line n n Prototype developed that works over a wire

4. SafeTalk System ADCCompressionEncryption Transmission FPGA DAC Decompression Decryption Reception FPGA wire

5. Analog-to-Digital Converter (ADC) n Sampling rate  8000 samples/s (Hz) n Low-pass filter with cutoff frequency of 3000 Hz n Linear quantization *Advantage: Easier to implement than a telephone codec *Disadvantage: Does not take into account whispering and shouting

6. Compression/Decompression n Dynamic compression based on volume *Low volume (quiet), use low-order 4-bits *High volume (loud), use high-order 4-bits *Compression ratio of 2:1 n Dynamic compression based on frequency *Low frequencies, less samples (1-in-8) *High frequencies, use 4-bits to represent *Compression ratio of 8:5

7. Encryption/Decryption n Stream cipher based on LFSRs and XOR n Advantages: *Adaptable for any frequency *Implementation less complex than other ciphers n Disadvantages: *Weak encryption algorithm *Hard coded key for LFSRs

8. Transmitter/Receiver n Universal Asynchronous Receiver Transmitter (UART) *Handles synchronization of data *Contains error checking features n Data Format *11-bit frame: 8-1-1 (data-parity-stop) n Transmission *Baud rate  85kbps *Practicality

9. Digital-to-Analog (DAC) n Convert 8-bit digital data into analog signal *Word range from 0 to 255 *Analog voltage range from 0 to 10V n Includes amplifier and filter *Low-pass filter with 3kHz cutoff n Final output from speaker

10. Achievements Analog-to-digital conversion  Encryption and decryption Transmission Digital-to-analog conversion SafeTalk prototype

11. SafeTalk (A Demonstration) Meow! ADC Enc. UART Tx UART Rx Decr. DAC Beep & Static