--- name: "Crypt::AuthEnc::EAX" 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::EAX" --- # Crypt::AuthEnc::EAX(3pm) Authenticated encryption in EAX mode ## NAME Crypt::AuthEnc::EAX - Authenticated encryption in EAX mode ## SYNOPSIS ``` ### OO interface use Crypt::AuthEnc::EAX; my $key = '...'; my $nonce = '...'; my $expected_tag = '...'; # encrypt and authenticate my $ae_enc = Crypt::AuthEnc::EAX->new("AES", $key, $nonce); $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::EAX->new("AES", $key, $nonce); $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::EAX qw(eax_encrypt_authenticate eax_decrypt_verify); my $key = '...'; my $nonce = '...'; my $adata = '...'; my $plaintext = '...'; my ($ciphertext, $tag) = eax_encrypt_authenticate('AES', $key, $nonce, $adata, $plaintext); my $decrypted = eax_decrypt_verify('AES', $key, $nonce, $adata, $ciphertext, $tag); ``` ## DESCRIPTION EAX is a mode that requires a cipher, CTR and OMAC support and provides encryption and authentication. It is initialized with a random IV that can be shared publicly, additional authenticated data which can be fixed and public, and a random secret symmetric key. This is a stateful API. Build one message by calling, in order: `"new"`, optional extra `"adata_add"`, zero or more `"encrypt_add"` or `"decrypt_add"` calls, then `"encrypt_done"` or `"decrypt_done"`. Use a fresh object per message. The optional `$adata` argument to `"new"` is equivalent to adding initial AAD before processing any payload. When verifying, `decrypt_done($expected_tag)` is the safer one-step form; `decrypt_done()` without arguments only returns the calculated tag. The first `"encrypt_done"` / `"decrypt_done"` call finalizes the object. After that, further `"adata_add"`, `"encrypt_add"`, `"decrypt_add"`, `"encrypt_done"`, and `"decrypt_done"` calls croak. ## EXPORT Nothing is exported by default. You can export selected functions: ``` use Crypt::AuthEnc::EAX qw(eax_encrypt_authenticate eax_decrypt_verify); ``` ## FUNCTIONS ### eax\_encrypt\_authenticate ``` my ($ciphertext, $tag) = eax_encrypt_authenticate($cipher, $key, $nonce, $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) # $nonce ... [binary string] unique nonce (no need to keep it secret) # $adata ... [binary string] additional authenticated data ``` ### eax\_decrypt\_verify ``` my $plaintext = eax_decrypt_verify($cipher, $key, $nonce, $adata, $ciphertext, $tag); # on error returns undef ``` ## METHODS Unless noted otherwise, assume `$ae` is an existing AEAD object created via `"new"`, for example: ``` my $ae = Crypt::AuthEnc::EAX->new($cipher, $key, $nonce); ``` ### new ``` my $ae = Crypt::AuthEnc::EAX->new($cipher, $key, $nonce); #or my $ae = Crypt::AuthEnc::EAX->new($cipher, $key, $nonce, $adata); # $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) # $nonce ... [binary string] unique nonce (no need to keep it secret) # $adata ... [binary string] additional authenticated data (optional) ``` ### adata\_add Can be called only before the first `"encrypt_add"` or `"decrypt_add"`. Returns the object itself (for chaining). ``` $ae->adata_add($adata); # 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 ``` **IMPORTANT:** The length of the tag is a security parameter and a zero-length tag is legal (it simply provides no authenticity), which is the caller's choice. ### 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) ``` ### 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::GCM, Crypt::AuthEnc::OCB - • \ - • \