File Coverage

blib/lib/Image/ExifTool/AES.pm

Criterion	Covered	Total	%
statement	97	162	59.8
branch	14	28	50.0
condition	9	15	60.0
subroutine	11	15	73.3
pod	1	13	7.6
total	132	233	56.6

#------------------------------------------------------------------------------
# File:         AES.pm
#
# Description:  AES encryption with cipher-block chaining
#
# Revisions:    2010/10/14 - P. Harvey Created
#
# References:   1) http://www.hoozi.com/Articles/AESEncryption.htm
#               2) http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf
#               3) http://www.faqs.org/rfcs/rfc3602.html
#------------------------------------------------------------------------------

package Image::ExifTool::AES;

use strict;
use vars qw($VERSION @ISA @EXPORT_OK);
require Exporter;

$VERSION = '1.01';
@ISA = qw(Exporter);
@EXPORT_OK = qw(Crypt);

my $seeded; # flag set if we already seeded random number generator
my $nr;     # number of rounds in AES cipher
my @cbc;    # cipher-block chaining bytes

# arrays (all unsigned character) to hold intermediate results during encryption
my @state = ([],[],[],[]);  # the 2-dimensional state array
my @RoundKey;               # round keys

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,
);

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

# the round constant word array, $rcon[i], contains the values given by
# x to the power (i-1) being powers of x (x is denoted as {02}) in the field GF(2^8)
# Note that i starts at 1, not 0).
my @rcon = (
    0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a,
    0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39,
    0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a,
    0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8,
    0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef,
    0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc,
    0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b,
    0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3,
    0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94,
    0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20,
    0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63, 0xc6, 0x97, 0x35,
    0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd, 0x61, 0xc2, 0x9f,
    0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb, 0x8d, 0x01, 0x02, 0x04,
    0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, 0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, 0x63,
    0xc6, 0x97, 0x35, 0x6a, 0xd4, 0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91, 0x39, 0x72, 0xe4, 0xd3, 0xbd,
    0x61, 0xc2, 0x9f, 0x25, 0x4a, 0x94, 0x33, 0x66, 0xcc, 0x83, 0x1d, 0x3a, 0x74, 0xe8, 0xcb,
);

#------------------------------------------------------------------------------
# This function produces 4*($nr+1) round keys.
# The round keys are used in each round to encrypt the states.
# Inputs: 0) key string (must be 16, 24 or 32 bytes long)
sub KeyExpansion($)
{
    my $key = shift;
    my @key = unpack 'C*', $key;        # convert the key into a byte array
    my $nk = int(length($key) / 4);     # number of 32-bit words in the key
    $nr = $nk + 6;                      # number of rounds

    # temporary variables (all unsigned characters)
    my ($i,@temp);

    # The first round key is the key itself.
    for ($i=0; $i<$nk; ++$i) {
        @RoundKey[$i*4..$i*4+3] = @key[$i*4..$i*4+3];
    }
    # All other round keys are found from the previous round keys.
    while ($i < (4 * ($nr+1))) {

        @temp[0..3] = @RoundKey[($i-1)*4..($i-1)*4+3];

        if ($i % $nk == 0) {
            # rotate the 4 bytes in a word to the left once
            # [a0,a1,a2,a3] becomes [a1,a2,a3,a0]
            @temp[0..3] = @temp[1,2,3,0];

            # take a four-byte input word and apply the S-box
            # to each of the four bytes to produce an output word.
            @temp[0..3] = @sbox[@temp[0..3]];

            $temp[0] = $temp[0] ^ $rcon[$i/$nk];

        } elsif ($nk > 6 && $i % $nk == 4) {

            @temp[0..3] = @sbox[@temp[0..3]];
        }
        $RoundKey[$i*4+0] = $RoundKey[($i-$nk)*4+0] ^ $temp[0];
        $RoundKey[$i*4+1] = $RoundKey[($i-$nk)*4+1] ^ $temp[1];
        $RoundKey[$i*4+2] = $RoundKey[($i-$nk)*4+2] ^ $temp[2];
        $RoundKey[$i*4+3] = $RoundKey[($i-$nk)*4+3] ^ $temp[3];
        ++$i;
    }
}

#------------------------------------------------------------------------------
# This function adds the round key to state.
# The round key is added to the state by an XOR function.
sub AddRoundKey($)
{
    my $round = shift;
    my ($i,$j);
    for ($i=0; $i<4; ++$i) {
        my $k = $round*16 + $i*4;
        for ($j=0; $j<4; ++$j) {
            $state[$j][$i] ^= $RoundKey[$k + $j];
        }
    }
}

#------------------------------------------------------------------------------
# Substitute the values in the state matrix with values in an S-box
sub SubBytes()
{
    my $i;
    for ($i=0; $i<4; ++$i) {
        @{$state[$i]}[0..3] = @sbox[@{$state[$i]}[0..3]];
    }
}

sub InvSubBytes()
{
    my $i;
    for ($i=0; $i<4; ++$i) {
        @{$state[$i]}[0..3] = @rsbox[@{$state[$i]}[0..3]];
    }
}

#------------------------------------------------------------------------------
# Shift the rows in the state to the left.
# Each row is shifted with different offset.
# Offset = Row number. So the first row is not shifted.
sub ShiftRows()
{
    # rotate first row 1 columns to left
    @{$state[1]}[0,1,2,3] = @{$state[1]}[1,2,3,0];

    # rotate second row 2 columns to left
    @{$state[2]}[0,1,2,3] = @{$state[2]}[2,3,0,1];

    # rotate third row 3 columns to left
    @{$state[3]}[0,1,2,3] = @{$state[3]}[3,0,1,2];
}

sub InvShiftRows()
{
    # rotate first row 1 columns to right
    @{$state[1]}[0,1,2,3] = @{$state[1]}[3,0,1,2];

    # rotate second row 2 columns to right
    @{$state[2]}[0,1,2,3] = @{$state[2]}[2,3,0,1];

    # rotate third row 3 columns to right
    @{$state[3]}[0,1,2,3] = @{$state[3]}[1,2,3,0];
}

#------------------------------------------------------------------------------
# Find the product of {02} and the argument to xtime modulo 0x1b
# Note: returns an integer which may need to be trimmed to 8 bits
sub xtime($)
{
    return ($_[0]<<1) ^ ((($_[0]>>7) & 1) * 0x1b);
}

#------------------------------------------------------------------------------
# Multiply numbers in the field GF(2^8)
sub Mult($$)
{
    my ($x, $y) = @_;
    return (($y & 1) * $x) ^
           (($y>>1 & 1) * xtime($x)) ^
           (($y>>2 & 1) * xtime(xtime($x))) ^
           (($y>>3 & 1) * xtime(xtime(xtime($x)))) ^
           (($y>>4 & 1) * xtime(xtime(xtime(xtime($x)))));
}

#------------------------------------------------------------------------------
# Mix the columns of the state matrix
sub MixColumns()
{
    my ($i,$t0,$t1,$t2);
    for ($i=0; $i<4; ++$i) {
        $t0 = $state[0][$i];
        $t2 = $state[0][$i] ^ $state[1][$i] ^ $state[2][$i] ^ $state[3][$i];
        $t1 = $state[0][$i] ^ $state[1][$i] ; $t1 = xtime($t1) & 0xff; $state[0][$i] ^= $t1 ^ $t2 ;
        $t1 = $state[1][$i] ^ $state[2][$i] ; $t1 = xtime($t1) & 0xff; $state[1][$i] ^= $t1 ^ $t2 ;
        $t1 = $state[2][$i] ^ $state[3][$i] ; $t1 = xtime($t1) & 0xff; $state[2][$i] ^= $t1 ^ $t2 ;
        $t1 = $state[3][$i] ^ $t0 ;           $t1 = xtime($t1) & 0xff; $state[3][$i] ^= $t1 ^ $t2 ;
    }
}

sub InvMixColumns()
{
    my $i;
    for ($i=0; $i<4; ++$i) {
        my $a = $state[0][$i];
        my $b = $state[1][$i];
        my $c = $state[2][$i];
        my $d = $state[3][$i];
        $state[0][$i] = (Mult($a,0x0e) ^ Mult($b,0x0b) ^ Mult($c,0x0d) ^ Mult($d,0x09)) & 0xff;
        $state[1][$i] = (Mult($a,0x09) ^ Mult($b,0x0e) ^ Mult($c,0x0b) ^ Mult($d,0x0d)) & 0xff;
        $state[2][$i] = (Mult($a,0x0d) ^ Mult($b,0x09) ^ Mult($c,0x0e) ^ Mult($d,0x0b)) & 0xff;
        $state[3][$i] = (Mult($a,0x0b) ^ Mult($b,0x0d) ^ Mult($c,0x09) ^ Mult($d,0x0e)) & 0xff;
    }
}

#------------------------------------------------------------------------------
# Encrypt (Cipher) or decrypt (InvCipher) a block of data with CBC
# Inputs: 0) string to cipher (must be 16 bytes long)
# Returns: cipher'd string
sub Cipher($)
{
    my @in = unpack 'C*', $_[0];    # unpack input plaintext
    my ($i, $j, $round);

    # copy the input PlainText to state array and apply the CBC
    for ($i=0; $i<4; ++$i) {
        for ($j=0; $j<4; ++$j) {
            my $k = $i*4 + $j;
            $state[$j][$i] = $in[$k] ^ $cbc[$k];
        }
    }

    # add the First round key to the state before starting the rounds
    AddRoundKey(0);

    # there will be $nr rounds; the first $nr-1 rounds are identical
    for ($round=1; ; ++$round) {
        SubBytes();
        ShiftRows();
        if ($round < $nr) {
            MixColumns();
            AddRoundKey($round);
        } else {
            # MixColumns() is not used in the last round
            AddRoundKey($nr);
            last;
        }
    }

    # the encryption process is over
    # copy the state array to output array (and save for CBC)
    for ($i=0; $i<4; ++$i) {
        for ($j=0; $j<4; ++$j) {
            $cbc[$i*4+$j] = $state[$j][$i];
        }
    }
    return pack 'C*', @cbc; # return packed ciphertext
}

sub InvCipher($)
{
    my @in = unpack 'C*', $_[0];    # unpack input ciphertext
    my (@out, $i, $j, $round);

    # copy the input CipherText to state array
    for ($i=0; $i<4; ++$i) {
        for ($j=0; $j<4; ++$j) {
            $state[$j][$i] = $in[$i*4 + $j];
        }
    }

    # add the First round key to the state before starting the rounds
    AddRoundKey($nr);

    # there will be $nr rounds; the first $nr-1 rounds are identical
    for ($round=$nr-1; ; --$round) {
        InvShiftRows();
        InvSubBytes();
        AddRoundKey($round);
        # InvMixColumns() is not used in the last round
        last if $round <= 0;
        InvMixColumns();
    }

    # copy the state array to output array and reverse the CBC
    for ($i=0; $i<4; ++$i) {
        for ($j=0; $j<4; ++$j) {
            my $k = $i*4 + $j;
            $out[$k] = $state[$j][$i] ^ $cbc[$k];
        }
    }
    @cbc = @in;             # update CBC for next block
    return pack 'C*', @out; # return packed plaintext
}

#------------------------------------------------------------------------------
# Encrypt/Decrypt using AES-CBC algorithm (with fixed 16-byte blocks)
# Inputs: 0) data reference (with leading 16-byte initialization vector when decrypting)
#         1) encryption key (16, 24 or 32 bytes for AES-128, AES-192 or AES-256)
#         2) encrypt flag (false for decryption, true with length 16 bytes to
#            encrypt using this as the CBC IV, or true with other length to
#            encrypt with a randomly-generated IV)
#         3) flag to disable padding
# Returns: error string, or undef on success
# Notes: encrypts/decrypts data in place (encrypted data returned with leading IV)
sub Crypt($$;$$)
{
    my ($dataPt, $key, $encrypt, $noPad) = @_;

    # validate key length
    my $keyLen = length $key;
    unless ($keyLen == 16 or $keyLen == 24 or $keyLen == 32) {
        return "Invalid AES key length ($keyLen)";
    }
    my $partLen = length($$dataPt) % 16;
    my ($pos, $i);
    if ($encrypt) {
        if (length($encrypt) == 16) {
            @cbc = unpack 'C*', $encrypt;
        } else {
            # generate a random 16-byte CBC initialization vector
            unless ($seeded) {
                srand(time() & ($$ + ($$<<15)));
                $seeded = 1;
            }
            for ($i=0; $i<16; ++$i) {
                $cbc[$i] = int(rand(256));
            }
            $encrypt = pack 'C*', @cbc;
        }
        $$dataPt = $encrypt . $$dataPt; # add IV to the start of the data
        # add required padding so we can recover the
        # original string length after decryption
        # (padding bytes have value set to padding length)
        my $padLen = 16 - $partLen;
        $$dataPt .= (chr($padLen)) x $padLen unless $padLen == 16 and $noPad;
        $pos = 16;      # start encrypting at byte 16 (after the IV)
    } elsif ($partLen) {
        return 'Invalid AES ciphertext length';
    } elsif (length $$dataPt >= 32) {
        # take the CBC initialization vector from the start of the data
        @cbc = unpack 'C16', $$dataPt;
        $$dataPt = substr($$dataPt, 16);
        $pos = 0;       # start decrypting from byte 0 (now that IV is removed)
    } else {
        $$dataPt = '';  # empty text
        return undef;
    }
    # the KeyExpansion routine must be called before encryption
    KeyExpansion($key);

    # loop through the data and convert in blocks
    my $dataLen = length $$dataPt;
    my $last = $dataLen - 16;
    my $func = $encrypt ? \&Cipher : \&InvCipher;
    while ($pos <= $last) {
        # cipher this block
        substr($$dataPt, $pos, 16) = &$func(substr($$dataPt, $pos, 16));
        $pos += 16;
    }
    unless ($encrypt or $noPad) {
        # remove padding if necessary (padding byte value gives length of padding)
        my $padLen = ord(substr($$dataPt, -1, 1));
        return 'AES decryption error (invalid pad byte)' if $padLen > 16;
        $$dataPt = substr($$dataPt, 0, $dataLen - $padLen);
    }
    return undef;
}

1; # end


__END__