Crypt::AuthEnc::GCM(3) User Contributed Perl Documentation 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 o CryptX, Crypt::AuthEnc::CCM, Crypt::AuthEnc::EAX, Crypt::AuthEnc::OCB o o perl v5.42.2 2026-06-18 Crypt::AuthEnc::GCM(3)