Image::ExifTool::AES

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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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

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>