#!/usr/bin/env perl
use MIME::Base64;
use POSIX qw(floor strftime mktime setlocale ceil);
#use warnings qw(uninitialized);

my $nBits = 256;
my $password = 'Ready to Have Some Fun';
my $ciphertext = 'DzQPUdLS0tKCWf9U6V/UDB3aQEUWCQ==';

print decrypt($ciphertext, $password, $nBits) . "\n";
exit;

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
#  AES counter (CTR) mode implementation in PHP (c) Chris Veness 2005-2011. Right of free use is */
#    granted for all commercial or non-commercial use under CC-BY licence. No warranty of any    */
#    form is offered.                                                                            */
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
#  
# 
# Encrypt a text using AES encryption in Counter mode of operation
#  - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
#
# Unicode multi-byte character safe
#
# @param plaintext source text to be encrypted
# @param password  the password to use to generate a key
# @param nBits     number of bits to be used in the key (128, 192, or 256)
# @return          encrypted text
#

# sBox is pre-computed multiplicative inverse in GF(2^8) used in subBytes and keyExpansion [§5.1.1]
my @sBox = (
        0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
        0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
        0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
        0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
        0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
        0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
        0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
        0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
        0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
        0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
        0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
        0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
        0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
        0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
        0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
        0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16
);

# rCon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [§5.2]
my @rCon = ( 
        (0x00, 0x00, 0x00, 0x00),
        (0x01, 0x00, 0x00, 0x00),
        (0x02, 0x00, 0x00, 0x00),
        (0x04, 0x00, 0x00, 0x00),
        (0x08, 0x00, 0x00, 0x00),
        (0x10, 0x00, 0x00, 0x00),
        (0x20, 0x00, 0x00, 0x00),
        (0x40, 0x00, 0x00, 0x00),
        (0x80, 0x00, 0x00, 0x00),
        (0x1b, 0x00, 0x00, 0x00),
        (0x36, 0x00, 0x00, 0x00) 
); 

#
# AES Cipher function: encrypt 'input' with Rijndael algorithm
#
# @param input message as byte-array (16 bytes)
# @param w     key schedule as 2D byte-array (Nr+1 x Nb bytes) - 
#              generated from the cipher key by keyExpansion()
# @return      ciphertext as byte-array (16 bytes)
#
sub cipher($$){    # main cipher function [§5.1]
        my($input, $w) = @_;
        my @w = @$w;
        my @input = @$input;
        my $Nb = 4;                 # block size (in words): no of columns in state (fixed at 4 for AES)
        my $Nr = scalar(@w)/$Nb - 1; # no of rounds: 10/12/14 for 128/192/256-bit keys

        my @state = ();  # initialise 4xNb byte-array 'state' with input [§3.4]
        for(my $i=0; $i<4*$Nb; $i++){
                $state[$i%4][floor($i/4)] = $input[$i];
        }
        my $state = addRoundKey(\@state, \@w, 0, $Nb);
        @state = @$state;
  
        for(my $round=1; $round<$Nr; $round++) {  # apply Nr rounds
                $state = subBytes(\@state, $Nb);
                @state = @$state;
                $state = shiftRows(\@state, $Nb);
                @state = @$state;
                $state = mixColumns(\@state, $Nb);
                @state = @$state;
                $state = addRoundKey(\@state, \@w, $round, $Nb);
                @state = @$state;
        }
        $state = subBytes(\@state, $Nb);
        @state = @$state;
        $state = shiftRows(\@state, $Nb);
        @state = @$state;
        $state = addRoundKey(\@state, @w, $Nr, $Nb);
        @state = @$state;

        my @output = (4*$Nb);  # convert state to 1-d array before returning [§3.4]
        for (my $i=0; $i<4*$Nb; $i++){
                $output[$i] = $state[$i%4][floor($i/4)];
        }
        return \@output;
}

sub addRoundKey() {  # xor Round Key into state S [§5.1.4]
        my($state, $w, $rnd, $Nb) = @_;
        my @w = @$w;
        my @state = @$state;
        for (my $r=0; $r<4; $r++) {
                for (my $c=0; $c<$Nb; $c++){
                        $state[$r][$c] ^= $w[$rnd*4+$c][$r];
                }
        }
        return \@state;
}
  
sub subBytes() {    # apply SBox to state S [§5.1.1]
        my($s, $Nb) = @_;
        my @s = @$s;
        for (my $r=0; $r<4; $r++) {
                for (my $c=0; $c<$Nb; $c++){
                        $s[$r][$c] = $sBox[$s[$r][$c]];
                }
        }
        return \@s;
}
  
sub shiftRows() {    # shift row r of state S left by r bytes [§5.1.2]
        my($s, $Nb) = @_;
        my @s = @$s;
        my @t = (4);#array
        for (my $r=1; $r<4; $r++) {
                for(my $c=0; $c<4; $c++){
                        $t[$c] = $s[$r][($c+$r)%$Nb];  # shift into temp copy
                }
                for(my $c=0; $c<4; $c++){
                        $s[$r][$c] = $t[$c];           # and copy back
                }
        }# note that this will work for Nb=4,5,6, but not 7,8 (always 4 for AES):
        return \@s;  # see fp.gladman.plus.com/cryptography_technology/rijndael/aes.spec.311.pdf 
}
  
sub mixColumns() {   # combine bytes of each col of state S [§5.1.3]
        my($s, $Nb) = @_;
        my @s = @$s;
        for(my $c=0; $c<4; $c++) {
                my @xa = (4);  # 'a' is a copy of the current column from 's'
                my @xb = (4);  # 'b' is a•{02} in GF(2^8)
                for(my $i=0; $i<4; $i++) {
                        $xa[$i] = $s[$i][$c];
                        $xb[$i] = $s[$i][$c]&0x80 ? $s[$i][$c]<<1 ^ 0x011b : $s[$i][$c]<<1;
                }

                # a[n] ^ b[n] is a•{03} in GF(2^8)
                $s[0][$c] = $xb[0] ^ $xa[1] ^ $xb[1] ^ $xa[2] ^ $xa[3]; # 2*a0 + 3*a1 + a2 + a3
                $s[1][$c] = $xa[0] ^ $b[1] ^ $xa[2] ^ $xb[2] ^ $xa[3]; # a0 * 2*a1 + 3*a2 + a3
                $s[2][$c] = $xa[0] ^ $xa[1] ^ $xb[2] ^ $xa[3] ^ $xb[3]; # a0 + a1 + 2*a2 + 3*a3
                $s[3][$c] = $xa[0] ^ $b[0] ^ $xa[1] ^ $xa[2] ^ $xb[3]; # 3*a0 + a1 + a2 + 2*a3
        }
        return \@s;
}

#
# Key expansion for Rijndael cipher(): performs key expansion on cipher key
# to generate a key schedule
#
# @param key cipher key byte-array (16 bytes)
# @return    key schedule as 2D byte-array (Nr+1 x Nb bytes)
#
sub keyExpansion($) {  # generate Key Schedule from Cipher Key [§5.2]
        my($key) = @_;
        my @key = @$key;
        my $Nb = 4;              # block size (in words): no of columns in state (fixed at 4 for AES)
        my $Nk = scalar(@key)/4;  # key length (in words): 4/6/8 for 128/192/256-bit keys
        my $Nr = $Nk + 6;        # no of rounds: 10/12/14 for 128/192/256-bit keys

        my @w = ();#array
        my @temp = ();#array

        for(my $i=0; $i<$Nk; $i++) {
                my @r = ($key[4*$i], $key[4*$i+1], $key[4*$i+2], $key[4*$i+3]);
                $w[$i] = @r;
        }

        for (my $i=$Nk; $i<($Nb*($Nr+1)); $i++) {
                $w[$i] = ();#array
                for (my $t=0; $t<4; $t++){
                        $temp[$t] = $w[$i-1][$t];
                }

                print "$i $Nk\n";
                #ERROR! WTF? => Illegal modulus zero
                next if(!$i or !$Nk);
                if($i && $Nk && $i % $Nk == 0){
                        my $temp = subWord(rotWord(\@temp));
                        @temp = @$temp;
                        for ($t=0; $t<4; $t++){
                                $temp[$t] ^= $rCon[$i/$Nk][$t];
                        }
                }elsif($Nk > 6 && $i%$Nk == 4) {
                        my $temp = subWord(\@temp);
                        @temp = @$temp;
                }
                for ($t=0; $t<4; $t++){
                        $w[$i][$t] = $w[$i-$Nk][$t] ^ $temp[$t];
                }
        }
        return \@w;
}

sub subWord() {    # apply SBox to 4-byte word w
        my($w) = @_;
        my @w = @$w;
        for ($i=0; $i<4; $i++){
                $w[$i] = $sBox[$w[$i]];
        }
        return \@w;
}

sub rotWord() {    # rotate 4-byte word w left by one byte
        my($w) = @_;
        my @w = @$w;
        my $tmp = $w[0];
        for ($i=0; $i<3; $i++){
                $w[$i] = $w[$i+1];
        }
        $w[3] = $tmp;
        return \@w;
}

# 
# Decrypt a text encrypted by AES in counter mode of operation
#
# @param ciphertext source text to be decrypted
# @param password   the password to use to generate a key
# @param nBits      number of bits to be used in the key (128, 192, or 256)
# @return           decrypted text
#
sub decrypt() {
        my($ciphertext, $password, $nBits) = @_;
        my $blockSize = 16;  # block size fixed at 16 bytes / 128 bits (Nb=4) for AES
        if (!($nBits==128 || $nBits==192 || $nBits==256)){
                return '';  # standard allows 128/192/256 bit keys
        }
        my $ciphertext = decode_base64($ciphertext);

        # use AES to encrypt password (mirroring encrypt routine)
        my $nBytes = $nBits/8;  # no bytes in key
        my @pwBytes = ();#array
        for ($i=0; $i<$nBytes; $i++){
                $pwBytes[$i] = ord(substr($password,$i,1)) & 0xff;
        }

        my $keyback = keyExpansion(\@pwBytes);
        @keyback = @$keyback;
        $key = cipher(\@pwBytes, \@keyback);
        @key = @$key;
        $key = (@key, ($key[0..$nBytes-16]));  # expand key to 16/24/32 bytes long
        @key = @$key;

        # recover nonce from 1st element of ciphertext
        my @counterBlock = ();#array
        $ctrTxt = substr($ciphertext, 0, 8);
        for ($i=0; $i<8; $i++){
                $counterBlock[$i] = ord(substr($ctrTxt,$i,1));
        }

        # generate key schedule
        my $keySchedule = keyExpansion(\@key);
        my @keySchedule = @$keySchedule;

        # separate ciphertext into blocks (skipping past initial 8 bytes)
        my $nBlocks = ceil((length($ciphertext)-8) / $blockSize);
        my @ct = ();#array
        for ($b=0; $b<$nBlocks; $b++){
                $ct[$b] = substr($ciphertext, 8+$b*$blockSize, 16);
        }
        $ciphertext = $ct;  # ciphertext is now array of block-length strings

        # plaintext will get generated block-by-block into array of block-length strings
        my @plaintxt = ();#array

        for (my $b=0; $b<$nBlocks; $b++) {
                # set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
                for (my $c=0; $c<4; $c++){
                        $counterBlock[15-$c] = urs($b, $c*8) & 0xff;
                }
                for (my $c=0; $c<4; $c++){
                        #ERROR! WTF? => Integer overflow in hexadecimal number
                        $counterBlock[15-$c-4] = urs(($b+1)/0x100000000-1, $c*8) & 0xff;
                }
                $cipherCntr = cipher(\@counterBlock, \@keySchedule);  # encrypt counter block
                @cipherCntr = @$cipherCntr;

                my @plaintxtByte = ();#array
                for (my $i=0; $i<length($ciphertext[$b]); $i++) {
                        # -- xor plaintext with ciphered counter byte-by-byte --
                        $plaintxtByte[$i] = $cipherCntr[$i] ^ ord(substr($ciphertext[$b],$i,1));
                        $plaintxtByte[$i] = chr($plaintxtByte[$i]);
                }
                $plaintxt[$b] = join('', $plaintxtByte); #php implode
        }
          
        # join array of blocks into single plaintext string
        $plaintext = join('',$plaintxt);#php implode
        return $plaintext;
}

#
# Unsigned right shift function, since PHP has neither >>> operator nor unsigned ints
#
# @param a  number to be shifted (32-bit integer)
# @param b  number of bits to shift a to the right (0..31)
# @return   a right-shifted and zero-filled by b bits
#
sub urs() {
        my($xa, $b) = @_;
        $xa &= 0xffffffff; $b &= 0x1f;  # (bounds check)
        if ($xa&0x80000000 && $b>0) {   # if left-most bit set
                $xa = ($xa>>1) & 0x7fffffff;   #   right-shift one bit & clear left-most bit
                $xa = $xa >> ($b-1);           #   remaining right-shifts
        }else{                       # otherwise
                $xa = ($xa>>$b);               #   use normal right-shift
        }
        return $xa;
}