cryptography - Which attacks are possible concerning my security layer concept?

Question

Despite all the advices to use SSL/https/etc. I decided to implement my own security layer on top of http for my application... The concept works as follows:

User registers -> a new RSA Keypair is generated
the Private Key gets encrypted with AES using the users login Password
(which the server doesnt know - it has only the sha256 for authentication...)

Server stores the hash of the users password
 and the Encrypted Private Key and Public Key

User logs in -> authenticates with nickname+password hash
(normal nick/password -> IP-bound sessionid authentication)
Server replies: sessionid, the Encrypted RSA Private Key
    and an Encrypted randomly generated Session Communication Password

Client decrypts the RSA Private Key with the users Password
Client decrypts the Session Communication Password with the RSA Private Key

---> From this point on the whole traffic gets AES-encrypted
     using that Session Password

I found no hole in that chain - neither the private key nor the login password get ever sent to the server as plaintext (I make no use of cookies, to exclude the possibility of the HTTP Cookie header to contain sensitive information)... but I am biased, so I ask - does my security implementation provide enough... security?

Answer 1

Why does everyone have to come up with their secure transport layer? What makes you think you've got something better than SSL or TLS? I simply do not understand the motivation to re-invent the wheel, which is a particularly dangerous thing to do when it comes to cryptography. HTTPS is a complex beast and it actually does a lot of work.

Remember, HTTPS also involves authentication (eg: being able to know you are actually talking to who you think you are talking to), which is why there exists a PKI and browsers are shipped with Root CA's. This is simply extremely difficult (if not impossible) to re-invent and prone to security holes. To answer you question, how are you defending against MITM attacks?

TLDR: Don't do it. SSL/TLS work just fine.

/endrant.