If you want to use CBC, you should take care that all but the last block have a length that is a multiple of the key length

No. The blocks passed to crypt have no relation to cypher blocks. The extra bytes will be buffered until the next call to crypt.

The start/crypt/finish mode allows you encrypt and decrypt arbitrary segments of the message (file) at a time, as long as you process the entire message from the start.

In fact, encrypt and decrypt are just thin wrappers around start/crypt/finish.

To circumvent these problems the "Cypher Block Chaining" was invented. [...] Which means that for every block (except the first one) you not only need the key to encrypt it, but also the preceding block.

Right, although Crypt::CBC normally uses a special value for the first block too: the salt.
Crypt::CBC uses salting to ensure that every message is encrypted with a different key.
Crypt::CBC uses chaining to ensure that every block is encrypted with a different key.

So if you want to decrypt CBC data you need reverse the encryption process exactly.

Aye, and he doesn't do that. If he really did want to add a line at a time, he'd file would have to look like 

length-of-encrypted-line, encrypted-line, length-of-encrypted-line, en
+crypted-line, ...

[download]

Each line would be a message that would be encrypted, and then decrypted individually (using encrypt and decrypt).

In reply to Re^2: line by line Encryption fun with Crypt::CBC and Rijndael? File Ownership issues? by ikegami
in thread line by line Encryption fun with Crypt::CBC and Rijndael? File Ownership issues? by hmbscully

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.