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mcrypt with CFB modes other than CFB8?

Posted: Fri Apr 18, 2008 3:59 pm
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.