Evolution: UID trust extrapolation attack on OpenPGP signatures

This article describes the UI deficiency of Evolution mail client that extrapolates the trust of one of OpenPGP key UIDs into the key itself, and reports it along with the (potentially untrusted) primary UID. This creates the possibility of tricking the user into trusting a phished mail via adding a forged UID to a key that has a previously trusted UID.

Continue reading

Identity with OpenPGP trust model

Let’s say you want to send a confidential message to me, and possibly receive a reply. Through employing asymmetric encryption, you can prevent a third party from reading its contents, even if it can intercept the ciphertext. Through signatures, you can verify the authenticity of the message, and therefore detect any possible tampering. But for all this to work, you need to be able to verify the authenticity of the public keys first. In other words, we need to be able to prevent the aforementioned third party — possibly capable of intercepting your communications and publishing a forged key with my credentials on it — from tricking you into using the wrong key.

This renders key authenticity the fundamental problem of asymmetric cryptography. But before we start discussing how key certification is implemented, we need to cover another fundamental issue — identity. After all, who am I — who is the person you are writing to? Are you writing to a person you’ve met? Or to a specific Gentoo developer? Author of some project? Before you can distinguish my authentic key from a forged key, you need to be able to clearly distinguish me from an impostor.

Continue reading “Identity with OpenPGP trust model”

Securing google-authenticator-libpam against reading secrets

I have recently worked on enabling 2-step authentication via SSH on the Gentoo developer machine. I have selected google-authenticator-libpam amongst different available implementations as it seemed the best maintained and having all the necessary features, including a friendly tool for users to configure it. However, its design has a weakness: it stores the secret unprotected in user’s home directory.

This means that if an attacker manages to gain at least temporary access to the filesystem with user’s privileges — through a malicious process, vulnerability or simply because someone left the computer unattended for a minute — he can trivially read the secret and therefore clone the token source without leaving a trace. It would completely defeat the purpose of the second step, and the user may not even notice until the attacker makes real use of the stolen secret.

Continue reading “Securing google-authenticator-libpam against reading secrets”

We mostly protect against script kiddie attacks

The recent efforts on improving the security of different areas of Gentoo have brought some arguments. Some time ago one of the developers has considered whether he would withstand physical violence if an attacker would use it in order to compromise Gentoo. A few days later another developer has suggested that an attacker could pay Gentoo developers to compromise the distribution. Is this a real threat to Gentoo? Are we all doomed?

Continue reading “We mostly protect against script kiddie attacks”