--- name: "Crypt::AuthEnc::GCM" section: "3pm" platform: "linux" package: "perl-cryptx" version: "0.091-2" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/Crypt::AuthEnc::GCM" --- # Crypt::AuthEnc::GCM(3pm) Authenticated encryption in GCM mode ## NAME Crypt::AuthEnc::GCM - Authenticated encryption in GCM mode ## SYNOPSIS ``` ### OO interface use Crypt::AuthEnc::GCM; my $key = '...'; my $iv = '...'; my $expected_tag = '...'; # encrypt and authenticate my $ae_enc = Crypt::AuthEnc::GCM->new("AES", $key, $iv); $ae_enc->adata_add('additional_authenticated_data1'); $ae_enc->adata_add('additional_authenticated_data2'); my $ct = $ae_enc->encrypt_add('data1'); $ct .= $ae_enc->encrypt_add('data2'); $ct .= $ae_enc->encrypt_add('data3'); my $tag = $ae_enc->encrypt_done(); # decrypt and verify my $ae_dec = Crypt::AuthEnc::GCM->new("AES", $key, $iv); $ae_dec->adata_add('additional_authenticated_data1'); $ae_dec->adata_add('additional_authenticated_data2'); my $pt = $ae_dec->decrypt_add('ciphertext1'); $pt .= $ae_dec->decrypt_add('ciphertext2'); $pt .= $ae_dec->decrypt_add('ciphertext3'); $ae_dec->decrypt_done($expected_tag) or die "decrypt failed"; # constant-time tag check #or, if you need the computed tag, compare it with slow_eq from Crypt::Misc #(Perl's 'eq' is not constant-time and leaks timing information) my $computed_tag = $ae_dec->decrypt_done(); die "decrypt failed" unless Crypt::Misc::slow_eq($computed_tag, $expected_tag); ### functional interface use Crypt::AuthEnc::GCM qw(gcm_encrypt_authenticate gcm_decrypt_verify); my $key = '...'; my $iv = '...'; my $adata = '...'; my $plaintext = '...'; my ($ciphertext, $tag) = gcm_encrypt_authenticate('AES', $key, $iv, $adata, $plaintext); my $decrypted = gcm_decrypt_verify('AES', $key, $iv, $adata, $ciphertext, $tag); ``` ## DESCRIPTION Galois/Counter Mode (GCM) - provides encryption and authentication. Use a fresh object per message unless you intentionally reuse the same key via `"reset"`. The normal call order is: `"new"`, one or more `"iv_add"` calls, optional `"adata_add"` calls, zero or more `"encrypt_add"` / `"decrypt_add"` calls, then `"encrypt_done"` / `"decrypt_done"`. The first `"encrypt_done"` / `"decrypt_done"` call finalizes the object. After that, further `"iv_add"`, `"adata_add"`, `"encrypt_add"`, `"decrypt_add"`, `"encrypt_done"`, and `"decrypt_done"` calls croak until you call `"reset"`. If you construct with `"new($cipher, $key)"`, you must provide the IV via `"iv_add"` before adding authenticated data or payload data. After `"reset"`, start a new message with the same key by supplying the IV again, and re-add AAD if needed. When verifying, `decrypt_done($expected_tag)` is the safer form. The no-argument form of `"decrypt_done"` only returns the computed tag. ## EXPORT Nothing is exported by default. You can export selected functions: ``` use Crypt::AuthEnc::GCM qw(gcm_encrypt_authenticate gcm_decrypt_verify); ``` ## FUNCTIONS ### gcm\_encrypt\_authenticate ``` my ($ciphertext, $tag) = gcm_encrypt_authenticate($cipher, $key, $iv, $adata, $plaintext); # $cipher .. [string] 'AES' or name of any other cipher with 16-byte block len # $key ..... [binary string] AES key of proper length (128/192/256 bits) # $iv ...... [binary string] initialization vector # $adata ... [binary string] additional authenticated data ``` ### gcm\_decrypt\_verify ``` my $plaintext = gcm_decrypt_verify($cipher, $key, $iv, $adata, $ciphertext, $tag); # on error returns undef ``` ## METHODS Unless noted otherwise, assume `$ae` is an existing AEAD object created via `"new"`, for example: ``` my $ae = Crypt::AuthEnc::GCM->new($cipher, $key, $iv); ``` ### new ``` my $ae = Crypt::AuthEnc::GCM->new($cipher, $key); #or my $ae = Crypt::AuthEnc::GCM->new($cipher, $key, $iv); # $cipher .. [string] 'AES' or name of any other cipher # $key ..... [binary string] encryption key of proper length # $iv ...... [binary string] initialization vector (optional, you can set it later via iv_add method) ``` ### iv\_add Set initialization vector (IV). Multiple calls are concatenated to form the full IV (the data is appended, not replaced). Returns the object itself. ``` $ae->iv_add($iv_data); # can be called multiple times before AAD/payload ``` Call `"iv_add"` before the first `"adata_add"`, `"encrypt_add"`, or `"decrypt_add"`. If you reuse the object via `"reset"`, provide the IV again for the new message. ### adata\_add Add **additional authenticated data**. Can be called **after** all `"iv_add"` calls but before the first `"encrypt_add"` or `"decrypt_add"`. Returns the object itself (for chaining). ``` $ae->adata_add($aad_data); # can be called multiple times ``` ### encrypt\_add Returns a binary string of ciphertext (raw bytes). ``` my $ciphertext = $ae->encrypt_add($data); # can be called multiple times ``` ### encrypt\_done Returns the authentication tag as a binary string (raw bytes). This call finalizes the current message. ``` my $tag = $ae->encrypt_done(); # returns $tag value ``` ### decrypt\_add Returns a binary string of plaintext (raw bytes). ``` my $plaintext = $ae->decrypt_add($ciphertext); # can be called multiple times ``` ### decrypt\_done Without argument returns the computed tag as a binary string. With `$tag` argument returns `1` (success) or `0` (failure). This call finalizes the current message. ``` my $tag = $ae->decrypt_done; # returns $tag value #or my $result = $ae->decrypt_done($tag); # returns 1 (success) or 0 (failure) ``` Use the `decrypt_done($tag)` form for authentication checks. The no-argument form only returns the computed tag. ### reset ``` $ae->reset; ``` Start a new message with the same key. After `"reset"`, call `"iv_add"` again, then `"adata_add"` if needed, before processing payload data. `"reset"` also clears the finalized state set by `"encrypt_done"` / `"decrypt_done"`. ### clone Returns a copy of the AEAD object in its current state. ``` my $ae_new = $ae->clone; ``` ## SEE ALSO - • CryptX, Crypt::AuthEnc::CCM, Crypt::AuthEnc::EAX, Crypt::AuthEnc::OCB - • \ - • \