Do not use AES in CBC mode for encrypting the username in Cookies

[jkakavas]

We currently use AES CBC by default in order to encrypt the username of the authenticated users in the encrypted session cookies. AES CBC protects only confidentiality and not the integrity ( authenticity ) and an attacker could be able to modify the encrypted value in order to authenticate as any other user.

We should use authenticated encryption instead

[007]

This may be as easy as specifying MODE_GCM as the default for https://github.com/rohe/pysaml2/blob/bc6d4cdacd0f66a68c2b0f7bdf9856387776dce8/src/saml2/aes.py#L31 and related calls in that file.

Commenting here as a pointer for anyone looking to implement, as well as for my own ToDo list.

[peppelinux]

luckily I use cookies inside a wrapper (django) to manage user sessions. I hope this topic has already had a follow up given its delicacy