Secure File Transfer

[Glauco]

hi to all,
i'm planning to make a way to transfer file with python.
I would like to make the transfer using some crypto api,
to make the channel secure.
i don't want to write a wrapper to ftp or to scp i just
want to make a new protocol, for a little application.

i took a quick look to some cryptographic modules available
in python (expecially pycrypto, gnupginterface, m2crypto)
and i'm now stuck on which one of these to choose.

Here's what i have in my mind: Alice wants to upload/download
some files from Bob.
Both of them have the public key (made with gpg), so in the
handshaking for the shared key is done using gpg.

After that the shared key is know to both the end of the channel
and they can use it to send the data.

i don't know what protocol (AES 3DES Blowfish? ) to use for the
transfer and i don't know if it could be better to implement
it directly with DSA/RSA rather than using GPG + somesymmetricprotocol

any suggestion hints example ?
Someone tried something like that ?

i'm using SocketServer for the network stuff so i would like to find
something wich can better suit with it


Many thanks for all the suggestion you can give me .


Samuele