diff --git a/src/doors/oxgen/Makefile b/src/doors/oxgen/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..ebb92e7ea829290f9b7cb69136658e7067eda69e
--- /dev/null
+++ b/src/doors/oxgen/Makefile
@@ -0,0 +1 @@
+oxgen: oxgen.c
diff --git a/src/doors/oxgen/oxgen.c b/src/doors/oxgen/oxgen.c
new file mode 100644
index 0000000000000000000000000000000000000000..fab2405a14a344810c2de242c61ea9de705896c5
--- /dev/null
+++ b/src/doors/oxgen/oxgen.c
@@ -0,0 +1,233 @@
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static uint32_t
+rotr(uint8_t cnt, uint32_t val)
+{
+ while (cnt) {
+ uint32_t hb = val & 1;
+ val >>= 1;
+ val |= hb << 31;
+ cnt--;
+ }
+ return val;
+}
+
+static uint32_t
+rotl(uint8_t cnt, uint32_t val)
+{
+ while (cnt) {
+ uint32_t hb = val & 0x80000000;
+ val <<= 1;
+ val |= hb >> 31;
+ cnt--;
+ }
+ return val;
+}
+
+static uint32_t
+get_user_nums(const char *str, uint16_t sub, uint16_t add, uint16_t rots)
+{
+ static const uint32_t keys[] = {
+ 0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,
+ 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
+ 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
+ 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
+ 0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
+ 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
+ 0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,
+ 0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
+ 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
+ 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
+ 0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,
+ 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
+ 0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116,
+ 0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
+ 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
+ 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
+ 0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A,
+ 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
+ 0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,
+ 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
+ 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
+ 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
+ 0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C,
+ 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
+ 0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
+ 0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
+ 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
+ 0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
+ 0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,
+ 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
+ 0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4,
+ 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
+ 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
+ 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
+ 0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
+ 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
+ 0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE,
+ 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
+ 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
+ 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
+ 0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252,
+ 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
+ 0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,
+ 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
+ 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
+ 0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
+ 0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04,
+ 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
+ 0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,
+ 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
+ 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
+ 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
+ 0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E,
+ 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
+ 0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
+ 0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
+ 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
+ 0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
+ 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,
+ 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
+ 0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,
+ 0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
+ 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
+ 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D,
+ };
+ uint32_t xor = 0xFFFFFFFF;
+ uint32_t tmp;
+ uint16_t num1;
+ uint16_t num2;
+ uint8_t ch;
+ const char *p;
+
+ for (p = str; *p; p++) {
+ ch = *(uint8_t *)p;
+ ch -= sub;
+ ch += add;
+ sub = (sub & 0xFF00) | (ch & 0xFF);
+ ch ^= (xor & 0xFF);
+ sub = (sub & 0x00FF) | ((ch & 0xFF) << 8);
+ xor = (xor & 0x0000FFFF) << 8;
+ xor ^= keys[sub>>8];
+ ch++;
+ }
+
+ xor = rotl(rotr(0x0b, rots & 0xF800), xor);
+ tmp = xor;
+
+ xor = 0;
+ xor |= rotl(0x05, tmp & 0x0001);
+ xor |= rotl(0x0d, tmp & 0x0002);
+ xor |= rotl(0x0f, tmp & 0x0004);
+ xor |= rotl(0x1c, tmp & 0x0008);
+ xor |= rotl(0x13, tmp & 0x0010);
+ xor |= rotl(0x18, tmp & 0x0020);
+ xor |= rotl(0x03, tmp & 0x0040);
+ xor |= rotl(0x09, tmp & 0x0080);
+ xor |= rotr(0x05, tmp & 0x0100);
+ xor |= rotl(0x01, tmp & 0x0200);
+ xor |= rotl(0x09, tmp & 0x0400);
+ xor |= rotl(0x11, tmp & 0x0800);
+ xor |= rotl(0x01, tmp & 0x1000);
+ xor |= rotl(0x07, tmp & 0x2000);
+ xor |= rotl(0x0b, tmp & 0x4000);
+ xor |= rotr(0x08, tmp & 0x8000);
+
+ xor |= rotl(0x05, tmp & 0x00010000);
+ xor |= rotr(0x0d, tmp & 0x00020000);
+ xor |= rotr(0x06, tmp & 0x00040000);
+ xor |= rotl(0x03, tmp & 0x00080000);
+ xor |= rotl(0x06, tmp & 0x00100000);
+ xor |= rotr(0x03, tmp & 0x00200000);
+ xor |= rotr(0x0e, tmp & 0x00400000);
+ xor |= rotr(0x17, tmp & 0x00800000);
+ xor |= rotl(0x06, tmp & 0x01000000);
+ xor |= rotr(0x01, tmp & 0x02000000);
+ xor |= rotl(0x01, tmp & 0x04000000);
+ xor |= rotr(0x0c, tmp & 0x08000000);
+ xor |= rotr(0x11, tmp & 0x10000000);
+ xor |= rotr(0x17, tmp & 0x20000000);
+ xor |= rotr(0x1c, tmp & 0x40000000);
+ xor |= rotr(0x1e, tmp & 0x80000000);
+
+ return xor;
+}
+
+static void
+strip_crlf(char *str)
+{
+ char *p;
+
+ p = strchr(str, '\r');
+ if (p)
+ *p = 0;
+ p = strchr(str, '\n');
+ if (p)
+ *p = 0;
+}
+
+int
+main(int argc, char **argv) {
+ uint32_t full;
+ uint16_t num1, num2, num3, num4;
+ char sysop[50];
+ char bbs[50];
+ char code[13];
+ const char alpha[] = "!@#ABCGHI<>?JKL\\[]MRSZ1234)+{7890-=NOPQ',./UV~$%^&*TWXY(}:\"D56EF";
+
+ printf("Sysop Name (40 chars max): ");
+ fflush(stdout);
+ if (fgets(sysop, sizeof(sysop), stdin) == NULL)
+ goto error;
+ if (strlen(sysop) > 40)
+ goto error;
+ strip_crlf(sysop);
+
+ printf("BBS Name (40 chars max): ");
+ fflush(stdout);
+ if (fgets(bbs, sizeof(bbs), stdin) == NULL)
+ goto error;
+ if (strlen(bbs) > 40)
+ goto error;
+ strip_crlf(bbs);
+
+ full = get_user_nums(sysop, 0xA705, 0x1b, 0xB8DD);
+ num1 = full >> 16;
+ num2 = full & 0xFFFF;
+ full = get_user_nums(bbs, 0, 0x7F, 0xC3F8);
+ num3 = full >> 16;
+ num4 = full & 0xFFFF;
+
+ code[12] = 0;
+
+ // The first six characters make up two 16-bit numbers.
+ code[0] = alpha[num1 >> 14];
+ code[1] = alpha[(num1 & 0x3F00) >> 8];
+ code[2] = alpha[(num1 & 0x00FC) >> 2];
+ code[3] = alpha[((num1 & 0x03) << 4) | (num2 >> 12)];
+ code[4] = alpha[(num2 & 0x0FC0) >> 6];
+ code[5] = alpha[(num2 & 0x003F)];
+
+ code[6] = alpha[num3 >> 14];
+ code[7] = alpha[(num3 & 0x3F00) >> 8];
+ code[8] = alpha[(num3 & 0x00FC) >> 2];
+ code[9] = alpha[((num3 & 0x03) << 4) | (num4 >> 12)];
+ code[10] = alpha[(num4 & 0x0FC0) >> 6];
+ code[11] = alpha[(num4 & 0x003F)];
+
+ printf("Code: %s\n", code);
+
+ return 0;
+
+error:
+ return 1;
+}
+
+// Bits we have...
+//543210 543210 543210 543210 543210 543210
+//xxxx00 000000 000000 001111 111111 111111
+//xxxxFE DCBA98 765432 10FEDC BA9876 543210
+//xxxx bits are scary missing ones.