Suppose I want to encrypt the voice data before sending using a ham radio, for example this unit.
Assume the encryption is simply AES encryption/decryption using predefined fixed key.
I am thinking of the following implementation:
1) Between the radio's transmitter/receiver and its logic unit, I'll place my circuit. 2) Low pass filter the signal then ADC it (with 10-bit accuracy, but this is irrelevant) with sampling frequency identical to that used by the radio. Ideally, this rate will already be higher than the max. freq. so as to avoid aliasing. 3) Apply the AES algorithm to each 128-bit segment of data. 4) DAC.
Going forward, I would implement some digital signature methods, thus signing the hash of the data, every 100 128-bit segment (or any other number). This will add 512-bit of data every 100*128 bits.
My question: 1) Is there any comment on the implementation, from a signal processing / communication point of view? 2) The added 512-bit signature will decrease the bit rate by (12800-512)/12800 => 4.16%. Is this a problem?