This is a custom encryption library. I do not know much about PHP's standard library of functions and was wondering if the following code can be improved in any way. The implementation should yield the same results, the API should remain as it is, but ways to make is more PHP-ish would be greatly appreciated.

Code

<?php
/***************************************
Create random major and minor SPICE key.
***************************************/
function crypt_major()
{
    $all = range("\x00", "\xFF");
    shuffle($all);
    $major_key = implode("", $all);
    return $major_key;
}
function crypt_minor()
{
    $sample = array();
    do
    {
        array_push($sample, 0, 1, 2, 3);
    } while (count($sample) != 256);
    shuffle($sample);
    $list = array();
    for ($index = 0; $index < 64; $index++)
    {
        $b12 = $sample[$index * 4] << 6;
        $b34 = $sample[$index * 4 + 1] << 4;
        $b56 = $sample[$index * 4 + 2] << 2;
        $b78 = $sample[$index * 4 + 3];
        array_push($list, $b12 + $b34 + $b56 + $b78);
    }
    $minor_key = implode("", array_map("chr", $list));
    return $minor_key;
}
/***************************************
Create the SPICE key via the given name.
***************************************/
function named_major($name)
{
    srand(crc32($name));
    return crypt_major();
}
function named_minor($name)
{
    srand(crc32($name));
    return crypt_minor();
}
/***************************************
Check validity for major and minor keys.
***************************************/
function _check_major($key)
{
    if (is_string($key) && strlen($key) == 256)
    {
        foreach (range("\x00", "\xFF") as $char)
        {
            if (substr_count($key, $char) == 0)
            {
                return FALSE;
            }
        }
        return TRUE;
    }
    return FALSE;
}
function _check_minor($key)
{
    if (is_string($key) && strlen($key) == 64)
    {
        $indexs = array();
        foreach (array_map("ord", str_split($key)) as $byte)
        {
            foreach (range(6, 0, 2) as $shift)
            {
                array_push($indexs, ($byte >> $shift) & 3);
            }
        }
        $dict = array_count_values($indexs);
        foreach (range(0, 3) as $index)
        {
            if ($dict[$index] != 64)
            {
                return FALSE;
            }
        }
        return TRUE;
    }
    return FALSE;
}
/***************************************
Create encode maps for encode functions.
***************************************/
function _encode_map_1($major)
{
    return array_map("ord", str_split($major));
}
function _encode_map_2($minor)
{
    $map_2 = array(array(), array(), array(), array());
    $list = array();
    foreach (array_map("ord", str_split($minor)) as $byte)
    {
        foreach (range(6, 0, 2) as $shift)
        {
            array_push($list, ($byte >> $shift) & 3);
        }
    }
    for ($byte = 0; $byte < 256; $byte++)
    {
        array_push($map_2[$list[$byte]], chr($byte));
    }
    return $map_2;
}
/***************************************
Create decode maps for decode functions.
***************************************/
function _decode_map_1($minor)
{
    $map_1 = array();
    foreach (array_map("ord", str_split($minor)) as $byte)
    {
        foreach (range(6, 0, 2) as $shift)
        {
            array_push($map_1, ($byte >> $shift) & 3);
        }
    }
    return $map_1;
}function _decode_map_2($major)
{
    $map_2 = array();
    $temp = array_map("ord", str_split($major));
    for ($byte = 0; $byte < 256; $byte++)
    {
        $map_2[$temp[$byte]] = chr($byte);
    }
    return $map_2;
}
/***************************************
Encrypt or decrypt the string with maps.
***************************************/
function _encode($string, $map_1, $map_2)
{
    $cache = "";
    foreach (str_split($string) as $char)
    {
        $byte = $map_1[ord($char)];
        foreach (range(6, 0, 2) as $shift)
        {
            $cache .= $map_2[($byte >> $shift) & 3][mt_rand(0, 63)];
        }
    }
    return $cache;
}
function _decode($string, $map_1, $map_2)
{
    $cache = "";
    $temp = str_split($string);
    for ($iter = 0; $iter < strlen($string) / 4; $iter++)
    {
        $b12 = $map_1[ord($temp[$iter * 4])] << 6;
        $b34 = $map_1[ord($temp[$iter * 4 + 1])] << 4;
        $b56 = $map_1[ord($temp[$iter * 4 + 2])] << 2;
        $b78 = $map_1[ord($temp[$iter * 4 + 3])];
        $cache .= $map_2[$b12 + $b34 + $b56 + $b78];
    }
    return $cache;
}
/***************************************
This is the public interface for coding.
***************************************/
function encode_string($string, $major, $minor)
{
    if (is_string($string))
    {
        if (_check_major($major) && _check_minor($minor))
        {
            $map_1 = _encode_map_1($major);
            $map_2 = _encode_map_2($minor);
            return _encode($string, $map_1, $map_2);
        }
    }
    return FALSE;
}
function decode_string($string, $major, $minor)
{
    if (is_string($string) && strlen($string) % 4 == 0)
    {
        if (_check_major($major) && _check_minor($minor))
        {
            $map_1 = _decode_map_1($minor);
            $map_2 = _decode_map_2($major);
            return _decode($string, $map_1, $map_2);
        }
    }
    return FALSE;
}
?>

This is a sample showing how the code is being used. Hex editors may be of help with the input / output.

Example

<?php
# get and process all of the form data
@ $input     = htmlspecialchars($_POST["input"]);
@ $majorname = htmlspecialchars($_POST["majorname"]);
@ $minorname = htmlspecialchars($_POST["minorname"]);
@ $majorkey  = htmlspecialchars($_POST["majorkey"]);
@ $minorkey  = htmlspecialchars($_POST["minorkey"]);
@ $output    = htmlspecialchars($_POST["output"]);
# process the submissions by operation
# CREATE
@ $operation = $_POST["operation"];
if ($operation == "Create")
{
    if (strlen($_POST["majorname"]) == 0)
    {
        $majorkey = bin2hex(crypt_major());
    }
    if (strlen($_POST["minorname"]) == 0)
    {
        $minorkey = bin2hex(crypt_minor());
    }
    if (strlen($_POST["majorname"]) != 0)
    {
        $majorkey = bin2hex(named_major($_POST["majorname"]));
    }
    if (strlen($_POST["minorname"]) != 0)
    {
        $minorkey = bin2hex(named_minor($_POST["minorname"]));
    }
}
# ENCRYPT or DECRYPT
function is_hex($char)
{
    if ($char == "0"):
        return TRUE;
    elseif ($char == "1"):
        return TRUE;
    elseif ($char == "2"):
        return TRUE;
    elseif ($char == "3"):
        return TRUE;
    elseif ($char == "4"):
        return TRUE;
    elseif ($char == "5"):
        return TRUE;
    elseif ($char == "6"):
        return TRUE;
    elseif ($char == "7"):
        return TRUE;
    elseif ($char == "8"):
        return TRUE;
    elseif ($char == "9"):
        return TRUE;
    elseif ($char == "a"):
        return TRUE;
    elseif ($char == "b"):
        return TRUE;
    elseif ($char == "c"):
        return TRUE;
    elseif ($char == "d"):
        return TRUE;
    elseif ($char == "e"):
        return TRUE;
    elseif ($char == "f"):
        return TRUE;
    else:
        return FALSE;
    endif;
}
function hex2bin($str)
{
    if (strlen($str) % 2 == 0):
        $string = strtolower($str);
    else:
        $string = strtolower("0" . $str);
    endif;
    $cache = "";
    $temp = str_split($str);
    for ($index = 0; $index < count($temp) / 2; $index++)
    {
        $h1 = $temp[$index * 2];
        if (is_hex($h1))
        {
            $h2 = $temp[$index * 2 + 1];
            if (is_hex($h2))
            {
                $cache .= chr(hexdec($h1 . $h2));
            }
            else
            {
                return FALSE;
            }
        }
        else
        {
            return FALSE;
        }
    }
    return $cache;
}
if ($operation == "Encrypt" || $operation == "Decrypt")
{
    # CHECK FOR ANY ERROR
    $errors = array();
    if (strlen($_POST["input"]) == 0)
    {
        $output = "";
    }
    $binmajor = hex2bin($_POST["majorkey"]);
    if (strlen($_POST["majorkey"]) == 0)
    {
        array_push($errors, "There must be a major key.");
    }
    elseif ($binmajor == FALSE)
    {
        array_push($errors, "The major key must be in hex.");
    }
    elseif (_check_major($binmajor) == FALSE)
    {
        array_push($errors, "The major key is corrupt.");
    }
    $binminor = hex2bin($_POST["minorkey"]);
    if (strlen($_POST["minorkey"]) == 0)
    {
        array_push($errors, "There must be a minor key.");
    }
    elseif ($binminor == FALSE)
    {
        array_push($errors, "The minor key must be in hex.");
    }
    elseif (_check_minor($binminor) == FALSE)
    {
        array_push($errors, "The minor key is corrupt.");
    }
    if ($_POST["operation"] == "Decrypt")
    {
        $bininput = hex2bin(str_replace("\r", "", str_replace("\n", "", $_POST["input"])));
        if ($bininput == FALSE)
        {
            if (strlen($_POST["input"]) != 0)
            {
                array_push($errors, "The input data must be in hex.");
            }
        }
        elseif (strlen($bininput) % 4 != 0)
        {
            array_push($errors, "The input data is corrupt.");
        }
    }
    if (count($errors) != 0)
    {
        # ERRORS ARE FOUND
        $output = "ERROR:";
        foreach ($errors as $error)
        {
            $output .= "\n" . $error;
        }
    }
    elseif (strlen($_POST["input"]) != 0)
    {
        # CONTINUE WORKING
        if ($_POST["operation"] == "Encrypt")
        {
            # ENCRYPT
            $output = substr(chunk_split(bin2hex(encode_string($_POST["input"], $binmajor, $binminor)), 58), 0, -2);
        }
        else
        {
            # DECRYPT
            $output = htmlspecialchars(decode_string($bininput, $binmajor, $binminor));
        }
    }
}
# echo the form with the values filled
echo "<P><TEXTAREA class=maintextarea name=input rows=25 cols=25>" . $input . "</TEXTAREA></P>\n";
echo "<P>Major Name:</P>\n";
echo "<P><INPUT id=textbox1 name=majorname value=\"" . $majorname . "\"></P>\n";
echo "<P>Minor Name:</P>\n";
echo "<P><INPUT id=textbox1 name=minorname value=\"" . $minorname . "\"></P>\n";
echo "<DIV style=\"TEXT-ALIGN: center\"><INPUT class=submit type=submit value=Create name=operation>\n";
echo "</DIV>\n";
echo "<P>Major Key:</P>\n";
echo "<P><INPUT id=textbox1 name=majorkey value=\"" . $majorkey . "\"></P>\n";
echo "<P>Minor Key:</P>\n";
echo "<P><INPUT id=textbox1 name=minorkey value=\"" . $minorkey . "\"></P>\n";
echo "<DIV style=\"TEXT-ALIGN: center\"><INPUT class=submit type=submit value=Encrypt name=operation> \n";
echo "<INPUT class=submit type=submit value=Decrypt name=operation> </DIV>\n";
echo "<P>Result:</P>\n";
echo "<P><TEXTAREA class=maintextarea name=output rows=25 readOnly cols=25>" . $output . "</TEXTAREA></P></DIV></FORM>\n";
?>

What should be editted for better memory efficiency or faster execution?