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SAFETALK

SAFETALK. Jodie Au Josh Chong Tam Paredes Jeff Sieben Amelia Yeoh. Introduction. Complete system designed to provide security from eavesdropping devices over a telephone line Prototype developed that works over a wire. SafeTalk System. Transmission. ADC. Compression. Encryption. FPGA.

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SAFETALK

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

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

  3. SafeTalk System Transmission ADC Compression Encryption FPGA wire Reception Decompression DAC Decryption FPGA

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

  5. Compression/Decompression • 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 • Dynamic compression based on frequency • Low frequencies, less samples (1-in-8) • High frequencies, use 4-bits to represent • Compression ratio of 8:5

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

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

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

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

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

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