EndCryptor, S/MIME and PGP under attack

We study here the exposure of a private key.

Exposure of a private key

The reader should recall that the exposure of a private key to an adversary exposes all communication that uses the shared secret calculated with this private key. In practice this means that in PGP and in S/MIME all communication sent to the victim are revealed to the adversary.

The S/MIME email encryption method uses a public key infrastructure (pki) which means that there is a Certificate Authority that digitally signs every new public key. Users already have the public key of the Certificate Authority and use this public key to verify the signature of a certificate that contains the new public key of a user. When a new public key is introduced it must first be certified by a Certificate Authority and then delivered in a certificate to a user.

In S/MIME and PGP the public keys are changed usually at intervals of years.

In EndCryptor at the beginning of the email exchange the user published long term public keys are responsible for the protection of the email. EndCryptor puts inside the first encrypted emails newly created short term public keys that initialize the patented protocol that continuously exchanges internal short term public keys when emails are being exchanged.

Suppose now that Alice starts communicating with Bob using EndCryptor and sends an encrypted email to Bob using Bob's long term public key. After receiving the email Bob replies to it. Later an adversary finds out Bob's long term private key. In EndCryptor only the first Alice's email to Bob can be decrypted by the adversary whereas the traditional systems expose all Alice's later emails to Bob which were sent to Bob’s public key.

Using our method the public keys are changed more frequently: if the parties communicate in turns one public key is used only once. An exposed private key has a very short life time in our solution. Our solution for the renewal of public keys is cost-free.

Using S/MIME or PGP one public key may be in use for many years.