##’end to end encryption’

There are three types of encryption: 1. Encryption in Transit 2. end to end encryption 3. end to end encrption(no service provider)
1. Encryption in Transit:

Alice —–encrypted—— service provider (no encrption) ——encrypted—— Bob

end to end encryption:

Alice —–encrypted—— service provider(encrypted) ——encrypted—— Bob

end to end encrption(no service provider)

Alice —–encrypted—— encrypted ——encrypted—— Bob

##the OTR 3-step Diffie-Hellman ratchet

      Alice                                             Bob
        g^a
[ encrypted message ]            ->       
[ next key advertisement ]                 
                                                        g^b
                                               [ encrypted message ]
                                   <-          [ Key Acknowledge ]
                                               [ next key advertisement ]
         g^c                                      
[ encrypted message ]
[ Key Acknowledge ]                ->
[ next key advertisement ]
                                                     ( k1, k2 ) = g^ab
                                                     ciphertext = ENCk1(msg)
                                                     ack = MACk2(something)

##Asyn hash ratchet

K1 = H(m)
K2 = H(K1)
K3 = H(K2) +That key material is sensitive, however, because it can be used to calculate the key material for every subsequent sequence number. So a client can’t hang on to it forever

##Signal’s 2-Step DH Ratchet (“Chain Keys”)

       Alice                                         Bob         [ Encrypted Message ]                   
    [ Current Ephememeral key ]     ->

[ Encrypted Message ]
<- [ Current Ephememeral key ]

+1. Alice generates a new ECDH ephemeral key A1 and uses it immediately to send a message. +2. Alice receives a message with Bob’s new ECDH ephemeral B1 and can then destroy A1 and generate A2 when sending her next message.

Meta Data

leaks of metadata can lead to great troubles.
NSA said “we kill people based on metadata”

Anonymous Communication with emphasis on TOR

 ------------------
 |  -------------  |
 |  |  --------- | |          |  |  |MESSAGE| | | 
 |  |  --------- | |   ciphertext = Epk1 [Epk2[Epk3[message]]]
 |  -------------  |
  -----------------

Sever 1 Sever 2 Sever 3

——————
| ————- | ———— | | ——— | | | ——– | ——- | | | M1 | | | | | M2 | | | M1| M2 | | ——— | | | ——– | ——- | ————- | ———— —————–

  ------------------
 |  -------------  |                  -----------
 |  |  --------- | |                 |   ------- |      Decrypt      |  |  |  M2   | | | Decrypt and     |   |  M3 | |      and               ------      D and p      |  |  --------- | | permutate       |   ------- |      permutate         | M2 |     ---->             M3      |  -------------  | --------------> -------------      --------->        ------
  -----------------
  ------------------
 |  -------------  |                 --------------
 |  |  --------- | |                |    --------  |                      -----      |  |  |   M3  | | |                |    |   M1 |  |                     | M3 |                        M1      |  |  --------- | |                |   --------   |                      ------
 |  -------------  |                ----------------
  -----------------