Crypt::Mode::CBC(3)

Crypt::Mode::CBC(3) 💖✨

okay bestie, this page comes straight from the User Contributed Perl Documentation corner of the perl-verse, and it's here to explain Crypt::Mode::CBC — the CBC cipher mode. it's giving block-cipher-chaining realness 💅

---

🎀 NAME 🎀

Crypt::Mode::CBC - Block cipher mode CBC [Cipher-block chaining]

🌸 SYNOPSIS 🌸

          use Crypt::Mode::CBC;
          my $m = Crypt::Mode::CBC->new('AES');
          my $key = '1234567890123456';
          my $iv = '1234567890123456';
          my $plaintext = 'example plaintext';
          my $chunk1 = 'example ';
          my $chunk2 = 'plaintext';

          # encrypt or decrypt in one call
          my $single_ciphertext = $m->encrypt($plaintext, $key, $iv);
          my $single_plaintext = $m->decrypt($single_ciphertext, $key, $iv);

          # encrypt more chunks
          $m->start_encrypt($key, $iv);
          my $chunked_ciphertext = '';
          $chunked_ciphertext .= $m->add($chunk1);
          $chunked_ciphertext .= $m->add($chunk2);
          $chunked_ciphertext .= $m->finish;

          # decrypt more chunks
          $m->start_decrypt($key, $iv);
          my $chunked_plaintext = '';
          $chunked_plaintext .= $m->add($chunked_ciphertext);
          $chunked_plaintext .= $m->finish;

🦋 DESCRIPTION 🦋

okay so this module implements CBC cipher mode. Note: it works only with ciphers from CryptX (Crypt::Cipher::NNNN). that's the whole vibe check, bestie 🫶

💅 METHODS 💅

unless noted otherwise, assume $m is an existing mode object created via new, for example:

        my $m = Crypt::Mode::CBC->new('AES');

---

✨ new ✨

this is your constructor moment, the main character entrance:

        my $m = Crypt::Mode::CBC->new($name);
        #or
        my $m = Crypt::Mode::CBC->new($name, $padding);
        #or
        my $m = Crypt::Mode::CBC->new($name, $padding, $cipher_rounds);

here's what those little arguments are serving:

• $name — [string] one of 'AES', 'Anubis', 'Blowfish', 'CAST5', 'Camellia', 'DES', 'DES_EDE', 'KASUMI', 'Khazad', 'MULTI2', 'Noekeon', 'RC2', 'RC5', 'RC6', 'SAFERP', 'SAFER_K128', 'SAFER_K64', 'SAFER_SK128', 'SAFER_SK64', 'SEED', 'Skipjack', 'Twofish', 'XTEA', 'IDEA', 'Serpent', or any <NAME> for which there is a Crypt::Cipher::<NAME> module.
• $padding — [integer] pick your padding era:
  • 0 — no padding (plaintext size has to be multiple of block length).
  • 1 — PKCS5 padding, Crypt::CBC's "standard" — DEFAULT.
  • 2 — Crypt::CBC's "oneandzeroes".
  • 3 — ANSI X.923 padding.
  • 4 — zero padding.
  • 5 — zero padding (+a block of zeros if the output length is divisible by the blocksize).
• $cipher_rounds — [integer] optional, number of rounds for given cipher.

🔐 encrypt 🔐

Encrypts the plaintext in a single call. Returns the ciphertext as a binary string. The plaintext scalar is converted to bytes using Perl's usual scalar stringification. Defined scalars, including numbers and string-overloaded objects, are accepted. undef is treated as an empty string and may emit Perl's usual "uninitialized value" warning.

          my $ciphertext = $m->encrypt($plaintext, $key, $iv);

🔓 decrypt 🔓

Decrypts the ciphertext in a single call. Returns the plaintext as a binary string. The ciphertext scalar is converted to bytes using Perl's usual scalar stringification. Defined scalars, including numbers and string-overloaded objects, are accepted. undef is treated as an empty string and may emit Perl's usual "uninitialized value" warning.

          my $plaintext = $m->decrypt($ciphertext, $key, $iv);

🚀 start_encrypt 🚀

Initializes encryption mode. Returns the object itself.

          $m->start_encrypt($key, $iv);

🧚 start_decrypt 🧚

Initializes decryption mode. Returns the object itself.

          $m->start_decrypt($key, $iv);

🍓 add 🍓

Feeds data to the encryption or decryption stream. Returns a binary string.

Each argument is converted to bytes using Perl's usual scalar stringification. Defined scalars, including numbers and string-overloaded objects, are accepted. undef is treated as an empty string and may emit Perl's usual "uninitialized value" warning.

          # in encrypt mode
          my $ciphertext = $m->add($plaintext);

          # in decrypt mode
          my $plaintext = $m->add($ciphertext);

🎀 finish 🎀

Finalizes the stream. In encryption mode, pads and encrypts the final block; in decryption mode, decrypts and removes padding from the final block. Returns the result as a binary string (may be empty if there is no data to flush).

          # encrypt more chunks
          $m->start_encrypt($key, $iv);
          my $chunk1 = 'example ';
          my $chunk2 = 'plaintext';
          my $ciphertext = '';
          $ciphertext .= $m->add($chunk1);
          $ciphertext .= $m->add($chunk2);
          $ciphertext .= $m->finish;

          # decrypt more chunks
          $m->start_decrypt($key, $iv);
          my $plaintext = '';
          $plaintext .= $m->add($ciphertext);
          $plaintext .= $m->finish;

🌈 SEE ALSO 🌈

• CryptX, Crypt::Cipher
• Crypt::Cipher::AES, Crypt::Cipher::Blowfish, ...
• <https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher-block_chaining_.28CBC.29>

---

xoxo bestie, that's the whole page 💖 it came from perl v5.42.0, dated 2026-05-11. slay responsibly 💅✨