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- #------------------------------------------------------------------------------
- # 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__
- =head1 NAME
- Image::ExifTool::AES - AES encryption with cipher-block chaining
- =head1 SYNOPSIS
- use Image::ExifTool::AES qw(Crypt);
- $err = Crypt(\$plaintext, $key, 1); # encryption
- $err = Crypt(\$ciphertext, $key); # decryption
- =head1 DESCRIPTION
- This module contains an implementation of the AES encryption/decryption
- algorithms with cipher-block chaining (CBC) and RFC 2898 PKCS #5 padding.
- This is the AESV2 and AESV3 encryption mode used in PDF documents.
- =head1 EXPORTS
- Exports nothing by default, but L</Crypt> may be exported.
- =head1 METHODS
- =head2 Crypt
- Implement AES encryption/decryption with cipher-block chaining.
- =over 4
- =item Inputs:
- 0) Scalar reference for data to encrypt/decrypt.
- 1) Encryption key string (must have length 16, 24 or 32).
- 2) [optional] Encrypt flag (false to decrypt).
- 3) [optional] Flag to avoid removing padding after decrypting, or to avoid
- adding 16 bytes of padding before encrypting when data length is already a
- multiple of 16 bytes.
- =item Returns:
- On success, the return value is undefined and the data is encrypted or
- decrypted as specified. Otherwise returns an error string and the data is
- left in an indeterminate state.
- =item Notes:
- The length of the encryption key dictates the AES mode, with lengths of 16,
- 24 and 32 bytes resulting in AES-128, AES-192 and AES-256.
- When encrypting, the input data may be any length and will be padded to an
- even 16-byte block size using the specified padding technique. If the
- encrypt flag has length 16, it is used as the initialization vector for
- the cipher-block chaining, otherwise a random IV is generated. Upon
- successful return the data will be encrypted, with the first 16 bytes of
- the data being the CBC IV.
- When decrypting, the input data begins with the 16-byte CBC initialization
- vector.
- =back
- =head1 BUGS
- This code is blindingly slow. But in truth, slowing down processing is the
- main purpose of encryption, so this really can't be considered a bug.
- =head1 AUTHOR
- Copyright 2003-2016, Phil Harvey (phil at owl.phy.queensu.ca)
- This library is free software; you can redistribute it and/or modify it
- under the same terms as Perl itself.
- =head1 REFERENCES
- =over 4
- =item L<http://www.hoozi.com/Articles/AESEncryption.htm>
- =item L<http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf>
- =item L<http://www.faqs.org/rfcs/rfc3602.html>
- =back
- =head1 SEE ALSO
- L<Image::ExifTool(3pm)|Image::ExifTool>
- =cut
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