Crypt::AuthEnc::EAX

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);

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

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;

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