NAME

       Image::ExifTool::AES - AES encryption with cipher-block chaining

SYNOPSIS

         use Image::ExifTool::AES qw(Crypt);

         $err = Crypt(\$plaintext, $key, 1);   # encryption

         $err = Crypt(\$ciphertext, $key);     # decryption

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.

EXPORTS

       Exports nothing by default, but "Crypt" may be exported.

METHODS

   Crypt
       Implement AES encryption/decryption with cipher-block chaining.

       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.

       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.

       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.

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.

AUTHOR

       Copyright 2003-2014, 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.

REFERENCES

       <http://www.hoozi.com/Articles/AESEncryption.htm>
       <http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf>
       <http://www.faqs.org/rfcs/rfc3602.html>

SEE ALSO

       Image::ExifTool(3pm)