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Add a simple emulateme for floating point operations #147

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Feb 17, 2024
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75 changes: 75 additions & 0 deletions src/rzil/emulatefloat.c
Original file line number Diff line number Diff line change
@@ -0,0 +1,75 @@
/**
* \file
* Simple crackme-like program, which decrypts a string in memory, but uses floating point operations to do so.
* The decryption loop is implemented to not make any external calls, so it can be emulated nicely.
* See emulateme.c for the the non-floating point instruction counterpart.
*/

#include <stdio.h>
#include <string.h>
#include <stdint.h>

#define LEN 0x10

char seckrit[LEN + 1] = { 0xe, 0xf, 0x3, 0xd, 0x1a, 0x6d, 0xf, 0x1a, 0xa, 0x4, 0x62, 0x34, 0xf, 0x3d, 0x29, 0x52 };

/* somewhat randomly generated numbers */
const double secondary_key[LEN] = { 8.99833709175345e-10, -0.3846771547676213, 2112271980.5789769, -2496373494.813322, 0.8743511441461778, -0.7300930961653576, -9705324222.854767, 0.5248033950772337, -712026204.430174, -0.04255897245519691, -8.307435687809127e-10, -0.22546719870688525, -0.8951827579358256, -8272556172.013981, 8.200744604338547e-10, 0.7577483159942799 };

int hash(double f) {
/* Get f to be >= 1 or >= -1, and then square it. */
if (f < 1 && f > -1) {
f = 1.0 / f;
}
f *= f;

/* Get the last byte of the rounded integer. */
int h = (int)f;
h &= 0xff;
return h;
}

void decrypt(const char *key) {
for (size_t i = 0; i < LEN; i++) {
double key_i = secondary_key[i];
int pad = hash(key_i);
seckrit[i] ^= (pad ^ key[i]);
}
}

#if INVERSE

int main() {
const char *key = "FloatLikeAButter";
const char *result = "Hello from RzIL!";

printf("char seckrit[LEN + 1] = { ");
for (size_t i = 0; i < LEN; i++) {
double key_i = secondary_key[i];
int pad = hash(key_i);

printf("%#02x, ", pad ^ key[i] ^ result[i]);
}
printf("};\n");

return 0;
}

#else

int main(int argc, const char *argv[]) {
if (argc != 2) {
printf("usage: %s [key]\n", argv[0]);
return 1;
}
const char *key = argv[1];
if (strlen(key) != LEN) {
printf("wrong length.\n");
return 1;
}
decrypt(key);
printf("Decrypted: %s\n", seckrit);
return 0;
}

#endif
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