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.\" ========================================================================
.\"
.IX Title "Crypt::AuthEnc::GCM 3pm"
.TH Crypt::AuthEnc::GCM 3pm 2024-03-07 "perl v5.38.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH NAME
Crypt::AuthEnc::GCM \- Authenticated encryption in GCM mode
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\& ### OO interface
\& use Crypt::AuthEnc::GCM;
\&
\& # encrypt and authenticate
\& my $ae = Crypt::AuthEnc::GCM\->new("AES", $key, $iv);
\& $ae\->adata_add(\*(Aqadditional_authenticated_data1\*(Aq);
\& $ae\->adata_add(\*(Aqadditional_authenticated_data2\*(Aq);
\& my $ct = $ae\->encrypt_add(\*(Aqdata1\*(Aq);
\& $ct .= $ae\->encrypt_add(\*(Aqdata2\*(Aq);
\& $ct .= $ae\->encrypt_add(\*(Aqdata3\*(Aq);
\& my $tag = $ae\->encrypt_done();
\&
\& # decrypt and verify
\& my $ae = Crypt::AuthEnc::GCM\->new("AES", $key, $iv);
\& $ae\->adata_add(\*(Aqadditional_authenticated_data1\*(Aq);
\& $ae\->adata_add(\*(Aqadditional_authenticated_data2\*(Aq);
\& my $pt = $ae\->decrypt_add(\*(Aqciphertext1\*(Aq);
\& $pt .= $ae\->decrypt_add(\*(Aqciphertext2\*(Aq);
\& $pt .= $ae\->decrypt_add(\*(Aqciphertext3\*(Aq);
\& my $tag = $ae\->decrypt_done();
\& die "decrypt failed" unless $tag eq $expected_tag;
\&
\& #or
\& my $result = $ae\->decrypt_done($expected_tag); # 0 or 1
\&
\& ### functional interface
\& use Crypt::AuthEnc::GCM qw(gcm_encrypt_authenticate gcm_decrypt_verify);
\&
\& my ($ciphertext, $tag) = gcm_encrypt_authenticate(\*(AqAES\*(Aq, $key, $iv, $adata, $plaintext);
\& my $plaintext = gcm_decrypt_verify(\*(AqAES\*(Aq, $key, $iv, $adata, $ciphertext, $tag);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
Galois/Counter Mode (GCM) \- provides encryption and authentication.
.SH EXPORT
.IX Header "EXPORT"
Nothing is exported by default.
.PP
You can export selected functions:
.PP
.Vb 1
\&  use Crypt::AuthEnc::GCM qw(gcm_encrypt_authenticate gcm_decrypt_verify);
.Ve
.SH FUNCTIONS
.IX Header "FUNCTIONS"
.SS gcm_encrypt_authenticate
.IX Subsection "gcm_encrypt_authenticate"
.Vb 1
\& my ($ciphertext, $tag) = gcm_encrypt_authenticate($cipher, $key, $iv, $adata, $plaintext);
\&
\& # $cipher .. \*(AqAES\*(Aq or name of any other cipher with 16\-byte block len
\& # $key ..... AES key of proper length (128/192/256bits)
\& # $iv ...... initialization vector
\& # $adata ... additional authenticated data
.Ve
.SS gcm_decrypt_verify
.IX Subsection "gcm_decrypt_verify"
.Vb 2
\& my $plaintext = gcm_decrypt_verify($cipher, $key, $iv, $adata, $ciphertext, $tag);
\& # on error returns undef
.Ve
.SH METHODS
.IX Header "METHODS"
.SS new
.IX Subsection "new"
.Vb 3
\& my $ae = Crypt::AuthEnc::GCM\->new($cipher, $key);
\& #or
\& my $ae = Crypt::AuthEnc::GCM\->new($cipher, $key, $iv);
\&
\& # $cipher .. \*(AqAES\*(Aq or name of any other cipher
\& # $key ..... encryption key of proper length
\& # $iv ...... initialization vector (optional, you can set it later via iv_add method)
.Ve
.SS iv_add
.IX Subsection "iv_add"
Set initialization vector (IV).
.PP
.Vb 1
\& $ae\->iv_add($iv_data);                        #can be called multiple times
.Ve
.SS adata_add
.IX Subsection "adata_add"
Add \fBadditional authenticated data\fR.
Can be called \fBafter\fR all \f(CW\*(C`iv_add\*(C'\fR calls but before the first \f(CW\*(C`encrypt_add\*(C'\fR or \f(CW\*(C`decrypt_add\*(C'\fR.
.PP
.Vb 1
\& $ae\->adata_add($aad_data);                    # can be called multiple times
.Ve
.SS encrypt_add
.IX Subsection "encrypt_add"
.Vb 1
\& $ciphertext = $ae\->encrypt_add($data);        # can be called multiple times
.Ve
.SS encrypt_done
.IX Subsection "encrypt_done"
.Vb 1
\& $tag = $ae\->encrypt_done();                   # returns $tag value
.Ve
.SS decrypt_add
.IX Subsection "decrypt_add"
.Vb 1
\& $plaintext = $ae\->decrypt_add($ciphertext);   # can be called multiple times
.Ve
.SS decrypt_done
.IX Subsection "decrypt_done"
.Vb 3
\& my $tag = $ae\->decrypt_done;           # returns $tag value
\& #or
\& my $result = $ae\->decrypt_done($tag);  # returns 1 (success) or 0 (failure)
.Ve
.SS reset
.IX Subsection "reset"
.Vb 1
\& $ae\->reset;
.Ve
.SS clone
.IX Subsection "clone"
.Vb 1
\& my $ae_new = $ae\->clone;
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
.IP \(bu 4
CryptX, Crypt::AuthEnc::CCM, Crypt::AuthEnc::EAX, Crypt::AuthEnc::OCB
.IP \(bu 4
<https://en.wikipedia.org/wiki/Galois/Counter_Mode>