Extracting a specific sequence of characters from an array
You can simply chop it up in place without requiring more than a few extra bytes of RAM using strtok():

char storebuffer[] = "ssid=abcdef&amp;pswd=ghijk";

// Slice it into two parts around the &amp;:
char *lefthalf = strtok(storebuffer, "&amp;");
if (lefthalf != NULL) { // We found a &amp; and split the string OK
    char *righthalf = strtok(NULL, "&amp;");

    // Now you can slice each half around the =
    char *ssidtag = strtok(lefthalf, "=");
    char *ssid = strtok(NULL, "=");
    char *pswdtag = strtok(righthalf, "=");
    char *pswdtag = strtok(NULL, "=");

    Serial.print("SSID: ");
    Serial.println(ssid);
    Serial.print("Password: ");
    Serial.println(pswd);
}


The existing string gets chopped up and the pointers point to different places:

ssid\0abcdef\0pswd\0ghijk
^     ^       ^     ^
1     2       3     4

1: ssidtag
2: ssid
3: pswdtag
4: pswd