From c871a79b98d13914886a6dbe44472bf1ce18e351 Mon Sep 17 00:00:00 2001 From: prototux Date: Thu, 1 Oct 2020 21:05:29 +0200 Subject: initial commit --- algo_uds_auth.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) create mode 100644 algo_uds_auth.c (limited to 'algo_uds_auth.c') diff --git a/algo_uds_auth.c b/algo_uds_auth.c new file mode 100644 index 0000000..1c4ffba --- /dev/null +++ b/algo_uds_auth.c @@ -0,0 +1,28 @@ +// UDS SA challenge-response implementation +// This should match the authentication between diagbox and any ECU +// Thanks to vlud for giving me the will to do it +#include + +// Transformation function with PSA not-so-secret sauce +int16_t transform(uint8_t data_msb, uint8_t data_lsb, uint8_t sec[]) +{ + int16_t data = (data_msb << 8) | data_lsb; + int32_t result = ((data % sec[0]) * sec[2]) - ((data / sec[0]) * sec[1]); + if (result < 0) + result += (sec[0] * sec[2]) + sec[1]; + return result; +} + +// Challenge reponse calculation for a given pin and challenge +// Challenge (seed) is 4 bytes and pin (key) is 2 bytes +uint32_t compute_response(uint8_t pin[], uint8_t chg[]) +{ + // Still hardcoded secrets + int8_t sec_1[3] = {0xB2, 0x3F, 0xAA}; + int8_t sec_2[3] = {0xB1, 0x02, 0xAB}; + + // Compute each 16b part of the response, with the twist, and return it + int16_t res_msb = transform(pin[0], pin[1], sec_1) | transform(chg[0], chg[3], sec_2); + int16_t res_lsb = transform(chg[1], chg[2], sec_1) | transform(res_msb>>8, res_msb&0xFF, sec_2); + return (msb << 16) | lsb; +} -- cgit v1.2.3