Crypt::AuthEnc::CCM(3pm)

NAME

Crypt::AuthEnc::CCM - Authenticated encryption in CCM mode

SYNOPSIS

 ### OO interface
 use Crypt::AuthEnc::CCM;
 my $key = '...';
 my $nonce = '...';
 my $adata = '...';
 my $tag_len = 16;
 my $pt_len = 15;
 my $expected_tag = '...';
 # encrypt and authenticate
 my $ae_enc = Crypt::AuthEnc::CCM->new("AES", $key, $nonce, $adata, $tag_len, $pt_len);
 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::CCM->new("AES", $key, $nonce, $adata, $tag_len, $pt_len);
 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::CCM qw(ccm_encrypt_authenticate ccm_decrypt_verify);
 my $key = '...';
 my $nonce = '...';
 my $adata = '...';
 my $plaintext = '...';
 my $tag_len = 16;
 my ($ciphertext, $tag) = ccm_encrypt_authenticate('AES', $key, $nonce, $adata, $tag_len, $plaintext);
 my $decrypted = ccm_decrypt_verify('AES', $key, $nonce, $adata, $ciphertext, $tag);

DESCRIPTION

CCM is an encrypt+authenticate mode that is built around using AES (or any 16-byte cipher) as a primitive. Unlike EAX and OCB mode, it is only meant for packet mode where the length of the input is known in advance.

Use a fresh object per message. The OO constructor requires all per-message parameters up front: key, nonce, associated data, tag length, and the exact total plaintext/ciphertext length that will be processed by "encrypt_add" / "decrypt_add". If you have no associated data in OO mode, pass ''.

When verifying, decrypt_done($expected_tag) is the safer form. The no-argument form of "decrypt_done" only returns the computed tag. The first "encrypt_done" / "decrypt_done" call finalizes the object. After that, further "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::CCM qw(ccm_encrypt_authenticate ccm_decrypt_verify);

FUNCTIONS

ccm_encrypt_authenticate

 my ($ciphertext, $tag) = ccm_encrypt_authenticate($cipher, $key, $nonce, $adata, $tag_len, $plaintext);
 # $cipher .. [string] 'AES' or name of any other cipher with 16-byte block len
 # $key ..... [binary string] key of proper length (e.g. 128/192/256 bits for AES)
 # $nonce ... [binary string] unique nonce/salt (no need to keep it secret)
 # $adata ... [binary string] additional authenticated data (C<undef> is treated the same as C<''>)
 # $tag_len . [integer] required length of output tag

CCM parameters should follow <https://csrc.nist.gov/pubs/sp/800/38/c/final>

 # tag length:   4, 6, 8, 10, 12, 14, 16 (reasonable minimum is 8)
 # nonce length: 7, 8, 9, 10, 11, 12, 13 (if you are not sure, use 11)
 # BEWARE nonce length determines max. enc/dec data size: max_data_size = 2^(8*(15-nonce_len))

The functional helper normalizes out-of-range $tag_len values to 16.

ccm_decrypt_verify

 my $plaintext = ccm_decrypt_verify($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 $ae = Crypt::AuthEnc::CCM->new($cipher, $key, $nonce, $adata, $pt_len);

new

 my $ae = Crypt::AuthEnc::CCM->new($cipher, $key, $nonce, $adata, $tag_len, $pt_len);
 # $cipher .. [string] 'AES' or name of any other cipher with 16-byte block len
 # $key ..... [binary string] key of proper length (e.g. 128/192/256 bits for AES)
 # $nonce ... [binary string] unique nonce/salt (no need to keep it secret)
 # $adata ... [binary string] additional authenticated data; must be a defined string scalar, use C<''> if none
 # $tag_len . [integer] tag length in bytes, validated as 1..16
 # $pt_len .. [integer] exact total plaintext/ciphertext length to encrypt/decrypt; must be >= 0

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.

clone

Returns a copy of the AEAD object in its current state.

 my $ae_new = $ae->clone;