# Image::ExifTool::AES - phpMan

## 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 2003-2022, Phil Harvey (philharvey66 at gmail.com)

    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)]