Perl

AES GCM Encrypt and Decrypt a File

See more Encryption Examples

Demonstrates how to AES GCM encrypt and decrypt a file. Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# This example assumes the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

my $crypt = Chilkat2::Crypt2->new;

# Set the encryption algorithm to "AES"
$crypt->CryptAlgorithm('aes');

# Indicate that the Galois/Counter Mode (GCM) should be used:
$crypt->CipherMode('gcm');

# KeyLength may be 128, 192, 256
$crypt->KeyLength(256);

# This is the 256-bit AES secret key (in hex format)
my $K = '000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F';

# This is the 16-byte initialization vector (in hex format)
my $IV = '000102030405060708090A0B0C0D0E0F';

# This is the OPTIONAL additional data (in hex format) to be used as input to the GCM AEAD algorithm,
# but is not included in the output.  It plays a role in the computation of the
# resulting authenticated tag.
my $AAD = 'feedfacedeadbeeffeedfacedeadbeefabaddad2';

# Set the secret key and IV
$crypt->SetEncodedIV($IV, 'hex');
$crypt->SetEncodedKey($K, 'hex');

# Set the additional authenticated data (AAD)
my $success = $crypt->SetEncodedAad($AAD, 'hex');

# Encrypt a file.
my $inFile = 'qa_data/hamlet.xml';
my $outFile = 'c:/temp/qa_output/hamlet_aes_gcm.enc';
$success = $crypt->CkEncryptFile($inFile, $outFile);
if (!$success) {
    print $crypt->LastErrorText, "\n";
    exit;
}

# Get the authentication tag in hex format
my $authTag = $crypt->GetEncodedAuthTag('hex');
print 'authentication tag = ', $authTag, "\n";

# Decrypt..

# Before decrypting, you must provide the expected authentication tag.
# The decrypt will fail if the resulting authentication tag computed while decrypting is not equal to the
# expected authentication tag.
$crypt->SetEncodedAuthTag($authTag, 'hex');

$inFile = $outFile;
$outFile = 'c:/temp/qa_output/hamlet_restored.xml';
$success = $crypt->CkDecryptFile($inFile, $outFile);
if (!$success) {
    print $crypt->LastErrorText, "\n";
    exit;
}

print "Success.\n";

# --------------------------------------------------------------------------------------------
# About AES-GCM:

# AES-GCM (Advanced Encryption Standard - Galois/Counter Mode) is a widely-used
# encryption mode that provides both confidentiality (encryption) and
# integrity/authentication (data integrity verification) in one operation. It is
# commonly used in secure communications due to its efficiency and strong security
# properties.
#
# Key Concepts:
#
#     AES (Advanced Encryption Standard):
#
#         AES is a symmetric encryption algorithm, meaning the same key is used
#         for both encryption and decryption.
#
#         It operates on fixed-size blocks of data (128 bits) using key sizes of
#         128, 192, or 256 bits.
#
#         In AES-GCM, AES is used to perform the actual data encryption.
#
#     GCM (Galois/Counter Mode):
#
#         Counter Mode (CTR): GCM uses counter mode for encryption. In this mode,
#         a nonce (or initialization vector, IV) and a counter are combined and encrypted
#         with AES. The result is XORed with the plaintext to produce the ciphertext.
#
#         Galois Mode (GMAC): GCM also includes an authentication mechanism based
#         on a Galois field. It generates an authentication tag, which ensures the
#         integrity of both the ciphertext and any additional data (called AAD -
#         Additional Authenticated Data). This tag is verified during decryption to ensure
#         that the data hasn't been tampered with.
#
# Key Features:
#
#     Confidentiality (Encryption):
#
#         The plaintext is encrypted using AES in counter mode. Each block of
#         plaintext is XORed with the output of AES applied to a combination of the IV and
#         an incremented counter.
#
#     Integrity (Authentication):
#
#         In addition to encryption, GCM provides authentication for both the
#         encrypted data (ciphertext) and any Additional Authenticated Data (AAD), such as
#         headers or metadata that need to be protected but not encrypted.
#
#         The authentication tag is generated using a Galois field multiplication
#         of the ciphertext and AAD. This ensures that any changes to the encrypted
#         message or the AAD will be detected during decryption.
#
# Key Components:
#
#     - Plaintext: The data you want to encrypt.
#     - Ciphertext: The encrypted data.
#     - Key: A symmetric key used for both encryption and decryption.
#     - Nonce/IV: A unique value used for each encryption to ensure security. It is not secret but should never be reused with the same key.
#     - AAD (Additional Authenticated Data): Optional data that is not encrypted but needs to be authenticated (e.g., headers).
#     - Authentication Tag: A tag generated to verify the integrity and authenticity of the ciphertext and AAD.