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Major update to EM4x70 support:

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1. Rework how communications with tag occur.
    a. bitstream to be sent to the tag is now fully pre-generated.
    b. bits sent and received are logged with start / end times.

2. Support built-in `hw dbg` for controlling verbosity of debug output

The new bitstream generation and logging has exposed a surprising legacy behavior ... each of the command that sent additional data (beyond the command) were:
* inserting an extra RM zero bit
* force-enabling command parity is used

This was not expected.  However, this PR maintains the behavior of the existing code.

TODO: Root-cause why the third RM bit is needed.  Fix code to remove that hack.

TODO: change the arm/client interface to ONLY use arrays of bytes, with well-defined content endianness, to avoid this problem.
This commit is contained in:
Henry Gabryjelski 2025-03-15 23:34:01 -07:00
commit 21ad101ff5
6 changed files with 2653 additions and 243 deletions
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40
include/em4x70.h
View file

@ -21,6 +21,7 @@
#include <stdint.h>
#include <stdbool.h>
#include <assert.h>
#define EM4X70_NUM_BLOCKS 16
@ -28,24 +29,36 @@
#define EM4X70_PIN_WORD_LOWER 10
#define EM4X70_PIN_WORD_UPPER 11
/// @brief Command transport structure for EM4x70 commands.
/// @details
/// This structure is used to transport data from the PC
/// to the proxmark3, and contain all data needed for
/// a given `lf em 4x70 ...` command to be processed
/// on the proxmark3.
/// The only requirement is that this structure remain
/// smaller than the NG buffer size (256 bytes).
typedef struct {
// ISSUE: `bool` type does not have a standard-defined size.
// therefore, compatibility between architectures /
// compilers is not guaranteed.
// ISSUE: C99 has no _Static_assert() ... was added in C11
// TODO: add _Static_assert(sizeof(bool)==1);
// TODO: add _Static_assert(sizeof(em4x70_data_t)==36);
bool parity;
// Used for writing address
uint8_t address;
// ISSUE: Presumes target is little-endian
// BUGBUG: Non-portable ... presumes stored in little-endian form!
uint16_t word;
// PIN to unlock
// BUGBUG: Non-portable ... presumes stored in little-endian form!
uint32_t pin;
// Used for authentication
//
// IoT safe subset of C++ would be helpful here,
// to support variable-bit-length integer types
// as integral integer types.
//
// Even C23 would work for this (GCC14+, Clang15+):
// _BitInt(56) rnd;
// _BitInt(28) frnd;
// _BitInt(20) grnd;
uint8_t frnd[4];
uint8_t grnd[3];
uint8_t rnd[7];
@ -54,9 +67,20 @@ typedef struct {
uint8_t crypt_key[12];
// used for bruteforce the partial key
// ISSUE: Presumes target is little-endian
// BUGBUG: Non-portable ... presumes stored in little-endian form!
uint16_t start_key;
} em4x70_data_t;
//_Static_assert(sizeof(em4x70_data_t) == 36);
// ISSUE: `bool` type does not have a standard-defined size.
// therefore, compatibility between architectures /
// compilers is not guaranteed.
// TODO: verify alignof(bool) == 1
//_Static_assert(sizeof(bool) == 1, "bool size mismatch");
typedef union {
uint8_t data[32];
} em4x70_tag_t;
//_Static_assert(sizeof(em4x70_tag_t) == 32, "em4x70_tag_t size mismatch");
#endif /* EM4X70_H__ */