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55 lines
1.3 KiB
C
55 lines
1.3 KiB
C
7 months ago
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#include <stdio.h>
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#include <string.h>
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#include <time.h>
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#include <stdlib.h>
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unsigned int MakeChecksum(unsigned char *buffer, int len)
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{
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unsigned int result;
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result = 0;
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for (int i = 0; i < len; i = i + 1) {
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result = (result << 3 | result >> 0x1d) ^ buffer[i];
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}
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return result;
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}
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//0: [CHECKSUM] - 4 bytes
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//[
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//4: [TIME] - 4 bytes
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//8: [PAYLOAD + HEADER LEN] - 1 byte
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//9: [TYPE] - 1 byte
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//10: [PAYLOAD LEN] - 1 byte
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//11: [PAYLOAD]
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//]
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int main() {
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unsigned char type = 0x2A;
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unsigned char payload[] = "g1mm3_th3_k3y";
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unsigned char payload_len = strlen(payload);
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unsigned char *flag_payload = malloc(payload_len);
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for (int i = 0; i < payload_len; ++i)
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flag_payload[i] = payload[i] ^ 42;
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unsigned char packet_len = payload_len + 7;
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time_t create_time = time(NULL);
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char *packet = calloc(payload_len + 0xb, sizeof(char));
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memcpy(&packet[11], flag_payload, payload_len);
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memcpy(&packet[10], &payload_len, 1);
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memcpy(&packet[9], &type, 1);
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memcpy(&packet[8], &packet_len, 1);
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memcpy(&packet[4], &create_time, 4);
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int crc = MakeChecksum(packet + 4, packet_len);
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memcpy(packet, &crc, 4);
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// Output
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fwrite(packet, 1, payload_len + 0xb, stdout);
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free(packet);
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free(flag_payload);
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}
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