mcrypt with CFB modes other than CFB8?

Discussions of secure PHP coding. Security in software is important, so don't be afraid to ask. And when answering: be anal. Nitpick. No security vulnerability is too small.

Moderator: General Moderators

Post Reply
zooper
Forum Newbie
Posts: 1
Joined: Fri Apr 18, 2008 3:54 pm

mcrypt with CFB modes other than CFB8?

Post by zooper »

When I call mcrypt_list_modes, one of the things it lists is "cfb". But "CFB" is not a mode; it's a family of modes.

Experiments (using the NIST's official test vectors) reveal that it's actually using CFB8.

But what if I need to use some other CFB mode?

For example, I am being sent data encrypted using AES256-CFB128. I have little choice in this fact. I would like to be able to decrypt it. But it seems like the closest I can come, without rolling my own encryption library or something like that, is AES256-CFB8, which quite simply will not work.

Any suggestions?

Thanks in advance for any help.
Post Reply