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CryptX-0.088_005
⭐ Starred 36 / Crypt::AuthEnc::CCM

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');
my $computed_tag = $ae_dec->decrypt_done();
die "decrypt failed" unless $computed_tag eq $expected_tag;

#or
my $result = $ae_dec->decrypt_done($expected_tag); # 0 or 1

### 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;

SEE ALSO