M17-FME is a stand-alone encoder and decoder of M17 Project protocol. M17-FME uses the open source Codec2 vocoder, and built on the specifications openly and freely provided under M17 Protocol Specifications. M17-FME should only be considered an 'educational' tool for radio enthusiasts and people interested in tinkering. It is also in an early beta stage, and as such, is prone to error and may have changing functionality over time as features are added, removed, reworked, etc. This tool should never be used for any commercial or critical needs, and any use for ill or malicious intent (jamming, DDOS, trolling, warfare, etc) is NOT CONDONED or TOLERATED!
Voice Stream Encoding and Decoding (RF Audio). Voice Stream Frames can be decoded from any RF Audio source, and M17-FME supports reading in from a Pulse Audio Input Source, OSS Input Source "/dev/dsp", SB16LE 48k/1 STDIN Input, TCP Linked SB16LE 48k/1 Network Source SDR++, sndfile compatible SB16LE 48k/1 .wav and .rrc files generated by any compatible M17 project source or recorded from OTA from an actual radio, float symbol input files generated by M17_Implementations, and dibit capture format (capture.bin) generated by DSD-FME.
When operating in encoding mode, Voice Stream can be modulated in FSK4 48k/1 SB16LE RF Audio output to Pulse Audio Sink, OSS Audio Sink, STDOUT, .wav file, float symbol output file, or dibit output file. Also, while in Encoding Mode, encoded data can also be sent back into the decoder via a loopback functionality which will, in turn, decode the encoded bitstream, with audio output being either decoded voice output, encoded RF output, or both through seperate output sinks, along with any file formats specified.
When operating in decoding mode, RF audio can be captured and saved with floating symbol output file, and decoded voice can be saved on a 'per call' basis with wav file creation for each new call after a no-sync period.
Voice Encoding and Decoding support both Codec2 3200 bps mode "full rate" and Codec2 1600 bps "half rate" modes, per specification. To encode in 1600 bps mode, the user on needs to specify some Arbitrary Data to the encoder, which is in turn handled as an embedded SMS message of up to 48 UTF-8 Characters to be decoded every superframe.
Packet Data Encoding and Decoding (RF Audio). Same input and output methods as listed above are available for Packet Data. Currently, only SMS text message protocol is expressely supported by Packet Data Encoding, while all standardized protocols (GNSS, etc) are decoded via the decoder if from another source. Users can encode an SMS message of up to 821 UTF-8 characters. Users can also enter raw encoded packet data as a string of hex octets to be encoded by the packet encoder (up to 823 octets). Packet Data can now also be easily entered (i.e., SMS text messages, or raw data) via the ncurses terminal during Stream Encoding or Duplex Mode, rather than at the CLI, which is still useful for one time data transmissions.
M17-FME is capable of transmitting and receiving UDP frames based on the specification linked above. This input and output has NOT BEEN TESTED on currently operating reflectors, and its status as working is unknown. M17-FME can however, communicate over UDP/IP Protocol to another M17-FME session.
NOTE: Encodng and Decoding of Packet Data over IP Frames has not been standardized in the M17 specifications, but operates with the same idea in mind as Voice Stream, where one UDP datagram is crafted with a complete LSF Link Data Setup, and the entire Packet Data contents are delivered all in one go.
A new simultaneous encoder and decoder routine has been written for M17-FME. Now, users can both encode and transmit, AND listen for and decode M17 traffic, either over RF, or via UDP/IP. Keep in mind, that a user can only use RF or IP, but not both at the same time for Duplex Mode operations. See below linked Example Usage for more information on using Duplex Mode. Most all functionality of the seperate encoder and decoder has been retained for Duplex Mode, with the exception of Voice Activated Transmit (Vox), which is only available on the pure encoder. Also, keep in mind that Duplex Mode will require the use of both the ncurses terminal AND the use of pulse audio, no other input or output methods will work with Duplex Mode due to its simultaneous encode and decode operations, and needing to gracefully open and close input and output streams on demand in the software.
M17-FME supports both the encryption and decryption of Voice Stream using AES and Scrambler modes per specification. M17-FME also (experimentally and unofficially) supports encryption and decryption of Packet Data using AES and Scrambler modes. The official stance from M17-FME is that encryption should be used as a tool, and in the context of M17-FME, it is available as a learning tool. When using encryption mode, M17-FME can craft and send your encryption key and encryption type as both a Packet, and embedded into Link Setup Data periodically in the clear. "Over the Air Key Delivery" or "OTAKD" was devised as a method to both allow and learn form the use of encryption, but to also freely and openly provide the encryption key to others to use while decoding. This 'format' is NOT per M17 specification, but is a method devised internally to allow the use of encryption while sharing the key for others. OTAKD can be enabled by using the -O command line option, or using the O or o keyboard shortcut in the Ncurses Terminal.
An emerging standard in M17 is the use of private and public keys to generate secp256r1 signatures and attach them to the tail end of transmissions. M17-FME can both encode and decode secp256r1 signatures using either private keys for encoding, public keys for decoding, or a combination of both. Users need only to generate and specify keys to be imported with the -k and -K option. See the included key folder for example keys. Keys can be generated in multiple ways, for example, using the command: openssl ecparam -name prime256v1 -genkey -noout -out keys.pem && openssl pkey -in keys.pem -text > keys.txt && rm keys.pem and then copy and pasting the resulting public and private key into txt files like in the example, or by using the -5 command line option. Note: Using the first method mentioned, on the public key, discard the first octet of the public key, or octet 0x04.
Similar to OTAKD for Encryption, OTASK format has been created for delivering signature public keys over the air. OTASK can be enabled at the command line via -Q option, or enabled or sent one time via the P and p options. Random Key Pairs can be generated at the command line via the -3 option as mentioned above and used during session, or generated for future use with the -5 command line option. Simialrly, Key Pairs can be generated in the Ncurses Terminal with the -3 keyboard shortcut, and enabled or sent one time with the P and p keys.
Please see Example Usage for a complete set of use case scenarios and configuration.
Please see Install Notes for information on cloning and compiling M17-FME.