package Crypt::AuthEnc::OCB; use strict; use warnings; our $VERSION = '0.091'; require Exporter; our @ISA = qw(Exporter); ### use Exporter 5.57 'import'; our %EXPORT_TAGS = ( all => [qw( ocb_encrypt_authenticate ocb_decrypt_verify )] ); our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } ); our @EXPORT = qw(); use Carp; $Carp::Internal{(__PACKAGE__)}++; use CryptX; # obsolete, only for backwards compatibility sub aad_add { goto &adata_add } sub blocksize { return 16 } sub CLONE_SKIP { 1 } # prevent cloning 1; =pod =head1 NAME Crypt::AuthEnc::OCB - Authenticated encryption in OCBv3 mode =head1 SYNOPSIS ### OO interface use Crypt::AuthEnc::OCB; my $key = '...'; my $nonce = '...'; my $tag_len = 16; my $expected_tag = '...'; # encrypt and authenticate my $ae_enc = Crypt::AuthEnc::OCB->new("AES", $key, $nonce, $tag_len); $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'); $ct .= $ae_enc->encrypt_last('rest of data'); my $tag = $ae_enc->encrypt_done(); # decrypt and verify my $ae_dec = Crypt::AuthEnc::OCB->new("AES", $key, $nonce, $tag_len); $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'); $pt .= $ae_dec->decrypt_last('rest of data'); $ae_dec->decrypt_done($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::OCB qw(ocb_encrypt_authenticate ocb_decrypt_verify); my $key = '...'; my $nonce = '...'; my $adata = '...'; my $plaintext = '...'; my $tag_len = 16; my ($ciphertext, $tag) = ocb_encrypt_authenticate('AES', $key, $nonce, $adata, $tag_len, $plaintext); my $decrypted = ocb_decrypt_verify('AES', $key, $nonce, $adata, $ciphertext, $tag); =head1 DESCRIPTION This module implements OCB v3 according to L. This is a stateful API. Build one message by calling, in order: C, optional C, zero or more C or C calls for full blocks, one optional C or C for the final partial block, then C or C. Use a fresh object per message. When verifying, C is the safer one-step form; C without arguments only returns the calculated tag. The first C / C call finalizes the object. After that, further C, C, C, C, C, C, and C calls croak. =head1 EXPORT Nothing is exported by default. You can export selected functions: use Crypt::AuthEnc::OCB qw(ocb_encrypt_authenticate ocb_decrypt_verify); =head1 FUNCTIONS =head2 ocb_encrypt_authenticate my ($ciphertext, $tag) = ocb_encrypt_authenticate($cipher, $key, $nonce, $adata, $tag_len, $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/salt (no need to keep it secret) # $adata ... [binary string] additional authenticated data # $tag_len . [integer] required length of output tag Use tag lengths from 4 to 16 bytes. Out-of-range values passed to this functional helper are normalized to 16. =head2 ocb_decrypt_verify my $plaintext = ocb_decrypt_verify($cipher, $key, $nonce, $adata, $ciphertext, $tag); # on error returns undef =head1 METHODS Unless noted otherwise, assume C<$ae> is an existing AEAD object created via C, for example: my $ae = Crypt::AuthEnc::OCB->new($cipher, $key, $nonce); =head2 new my $ae = Crypt::AuthEnc::OCB->new($cipher, $key, $nonce, $tag_len); # $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/salt (no need to keep it secret) # $tag_len . [integer] required length of output tag B 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. =head2 adata_add Can be called only before the first C, C, C, or C. Returns the object itself (for chaining). $ae->adata_add($adata); #can be called multiple times =head2 encrypt_add Returns a binary string of ciphertext (raw bytes). my $ciphertext = $ae->encrypt_add($data); # can be called multiple times # note: \ must be a multiple of the block length (16 for AES) =head2 encrypt_last my $ciphertext = $ae->encrypt_last($data); =head2 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 =head2 decrypt_add Returns a binary string of plaintext (raw bytes). my $plaintext = $ae->decrypt_add($ciphertext); # can be called multiple times # note: \ must be a multiple of the block length (16 for AES) =head2 decrypt_last my $plaintext = $ae->decrypt_last($data); =head2 decrypt_done Without argument returns the computed tag as a binary string. With C<$tag> argument returns C<1> (success) or C<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) =head2 blocksize my $bs = $ae->blocksize; # always returns 16 Returns the block size of the underlying cipher (always 16, since OCB requires a 128-bit block cipher such as AES). =head2 clone Returns a copy of the AEAD object in its current state. my $ae_new = $ae->clone; =head1 SEE ALSO =over =item * L, L, L, L =item * L =item * L =back =cut