How SSH works:

1. When the first time a user A on machine M1 connects to machine M2,
	M1 obtains the public key of M2 (1024 bits typically);
	M2's SSH software generates the public key for M2;

2. The SSH client software generates a random session key (the random
	generation algorith matters), and send it to the host;

3. The session key is then used to encrypt all subsequent messages, using
	either DES, triple DES, or anything else;


Vulnerable to "Man in the Middle" attack at the very-first time logon;


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How SSL works:

1. Client (the Browser) sends in a Hello message, including a random number
	(28 bytes);

2. Server responses with a Hello message, also including another random
	number (28 bytes);

3. Server sends its public key, with Verisign's signature;

4. (Optional) clients also send server its public key;

5. Browser picks a random key (called pre-master secret, it is 48 bytes), 
	sends it to the server (encrypted with the server's public key);


The problem with this step is that it doesn't have "forward secrecy".
So this step can be changed with Diffe-Hellman.

Client pick g^a mod p, sends it to server; server picks g^b mod p, sign with
secret key, and sends it to client; 

the premaster secret is g^ab mod p;

This way, even if the server is broken into, they can't find the g^ab mod p;


Also, for Diffe-Hellman, a and b must be over 160 bits.  because there exists
an algorithm that can calculate discrete log for 2^k/2 bits for k bits;



6. From the random key, both calculate F(CR, SR, Pre-Master), and get a
	master secret; 

"master_secret =
       MD5(pre_master_secret + SHA('A' + pre_master_secret +
           ClientHello.random + ServerHello.random)) +
       MD5(pre_master_secret + SHA('BB' + pre_master_secret +
           ClientHello.random + ServerHello.random)) +
       MD5(pre_master_secret + SHA('CCC' + pre_master_secret +
           ClientHello.random + ServerHello.random));"


7. Master secret is 48 bytes, hashed into a sequence of secure bytes, which
	are then assigned to the MAC key, session key, and the initialization
	vector;

	"CipherSpecs require
   a client write MAC secret, a server write MAC secret, a client
   write key, a server write key, a client write IV, and a server
   write IV, which are generated from the master secret in that order."


	"key_block =
       MD5(master_secret + SHA(`A' + master_secret +
                               ServerHello.random +
                               ClientHello.random)) +
       MD5(master_secret + SHA(`BB' + master_secret +
                               ServerHello.random +
                               ClientHello.random)) +
       MD5(master_secret + SHA(`CCC' + master_secret +
                               ServerHello.random +
                               ClientHello.random)) + [...];"


	"client_write_MAC_secret[CipherSpec.hash_size]
     server_write_MAC_secret[CipherSpec.hash_size]
     client_write_key[CipherSpec.key_material]
     server_write_key[CipherSpec.key_material]
     client_write_IV[CipherSpec.IV_size] /* non-export ciphers */
     server_write_IV[CipherSpec.IV_size] /* non-export ciphers */"



Remember what IVs, session keys and MAC secrets are used for?...



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. Authentication must include session key exchange;


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Passwords:

. One time pads;

. S-key: 
	1. Host picks a random number, hashes it 1000 times;

	2. Host gives the random number to user;

		this happens at account-assignment time;



	3. The nth time that the user logs on, it sends in 1000-n'th hash
		of the random number;

	4. server remembers which time the user has logged on;

	
   Advantage: even if server is broken into, attacker cannot fake as user
	to log on, because it is a one-way hash function;

   Disadvantage: limited time of log-on;

. SecureID: a shared secret between users and the host, rehashed every minute;

	requires clock synchronization between the two;
	server maintains clock number for each card;
	maximum drift in clock value;


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PGP by Phil Zimmerman (pgpi.com):

. Used to use RSA, but now use Diffe-Hellman;

. When a message is sent, put in g^b mod p, and encrypt message with
	g^ab mod p;

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