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Data Encryption with SSL/TLS: Understanding Secure Sockets Layer Basics

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  1. Network Programming Kansas State University at Salina Data Encryption using SSLTopic 5, Chapter 15

  2. SSL • Secure Sockets Layer (SSL)Transport Layer Security (TLS) • Based on public certificates and private keys • Certificates may be either self signed or verified by one of a few trusted Certificate Authorities (CA) • Often used with HTTP (https://www...)Can be used with SMTP, ssh, scp, any client server communication. • Python has basic SSL client capability. OpenSSL module provides more. Re-worked in Python 2.6 to also include server side support.

  3. How it works • Client and server establish socket connection • Server sends public certificate to client • To verify authenticity of the server, client may validate the certificate with one a few trusted certificate authorities • Client encrypts the message using the public key and sends it to the server • Server receives the message and decrypts it using the private key

  4. Public / Private Keys • The keys are a matched pair • Messages encrypted with the public key can only be decrypted with the private key • Having the public key will not help decrypt a message • Keys may be self signed for private activities • Public servers usually have purchased certificates • In many cases, especially with HTTP, the message is only encrypted from client to server. Thus, the credit card number is usually ‘X’ed out in the receipt.

  5. Self Signing a certificate 1010 timber:~/openssl> openssl req -new -out certfile.pem -keyout keyfile.pem Generating a 1024 bit RSA private key ........++++++ ................................................++++++ writing new private key to 'keyfile.pem' Enter PEM pass phrase: Verifying - Enter PEM pass phrase: ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [GB]:US State or Province Name (full name) [Berkshire]:Kansas Locality Name (eg, city) [Newbury]:Salina Organization Name (eg, company) [My Company Ltd]:Kansas State University Organizational Unit Name (eg, section) []:Engineering Technology Common Name (eg, your name or your server's hostname) []:timber.sal.ksu.edu Email Address []:tim@ksu.edu Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []: An optional company name []:

  6. Public Certificate and Private Key 1011 timber:~/openssl> cat certfile.pem -----BEGIN CERTIFICATE REQUEST----- MIIB7DCCAVUCAQAwgasxCzAJBgNVBAYTAlVTMQ8wDQYDVQQIEwZLYW5zYXMxDzAN BgNVBAcTBlNhbGluYTEgMB4GA1UEChMXS2Fuc2FzIFN0YXRlIFVuaXZlcnNpdHkx HzAdBgNVBAsTFkVuZ2luZWVyaW5nIFRlY2hub2xvZ3kxGzAZBgNVBAMTEnRpbWJl ci5zYWwua3N1LmVkdTEaMBgGCSqGSIb3DQEJARYLdGltQGtzdS5lZHUwgZ8wDQYJ KoZIhvcNAQEBBQADgY0AMIGJAoGBAOTRJmntlJy7cf3N3yW0/1jSUoWROlVkaZfg Aojz59gKlEDMLtVn2DKYDexWe0AUV9gBEpHTguX5Vi322IpPjOvO/3n1kHrdgD5L Nnc9tYYe5fF0RKzisRz7HKu6aXXY6dNFJMVRj7cTg4uSh7IS5lJvDCjohEnPJYzF 2g8mSoSBAgMBAAGgADANBgkqhkiG9w0BAQQFAAOBgQC1BjorEY98HkW7ceyH9s3d EcFy6uFKXP2hFjCEesrW+N8lMdyrXYbyxffdE6ZpMEcNoYS9S0wxuwg1f7WjI/3S y+fA2yviU+7c7blBd7r/r8uaviJB3uMWTgWKdnKBsnqBRvUQcytSrflzANV0MHIq tVhFOv/lfqxQIha0m6BFQw== -----END CERTIFICATE REQUEST----- 1012 timber:~/openssl> cat keyfile.pem -----BEGIN RSA PRIVATE KEY----- Proc-Type: 4,ENCRYPTED DEK-Info: DES-EDE3-CBC,F7FFBD69A863B27B oq2s6YBa+6XVk+sfhFwYQixYQnP1wDDPVFpf+gdFTQUZ7qkG+qeR23z9LqEiTm1H E5ZB8TW3m1PC8Bhz8EansTV9/Q2AqpgWduytuKX9mo1nEwjTQPx7vZpnb+JrcGB2 Ew2qp4NfU1sYVpXV+KO66TunsTdhvNyV1fH8r6Dgk9xruNfvoUB0WRRKDGZ17iaP 1GeGPnQWWDC7WWE2LYugz/LW5BSoZtwdYf2U/48F/SvAgf1MyPUExwBqYRinzjdo PP9MXMGPHJQJ9PLeGnIRqUAAU2p0NJB8tb8ZrwFWpK4Aa1B3I9cNiMa42L0mfcax Y10+0MMq4UcAIHkfdIOBbRN8m9lpM3haeAs9ppAewyG3MKII2DC+FsEsdYIBWRhL Mfi3WcUOwqrVHLL2Qf1d4QZS9MkYZahvKsz3iYGZkw2Le/BXy+0/esLFnCjDhEOA NLLrVRcpo+82bKjjeQf4yTxL6w++HmfWsWSSGgD+BLWx6geVDZsUS65XaNsUsHQ7 PPi2taqaTu+rHKbYBoTdZUi3gUHhzH5NlWBvOe3tyWMVtid+GgmI418ib5uOikYL c//IjhwrVzUL4+9raSVcHqFn+kOX/bGxbDzr5vJSJSDFfff2dwYAFvsPYK2ka5gZ rYdq2tGjrEQycNXksOqsVGv4JEsuEacXeQRpVqh6AOVEWbC0eTUA1bjo9wM6aywi FIqgr0lLIE7lvL9rW8mkPQ9Tl9lwrLZfqB3vcfmstDXfQqH/A9VEgjhbNHnJkZ3n MihuBRizFEbK/kZRbk0yVMiFU6HltIJUgJ5b06bLEpcz6wlHSBBxhA== -----END RSA PRIVATE KEY-----

  7. Programming SSL • Client Side • Limited support in built-in socket module • ssl = socket.ssl( socket ) • Two methods: read(), write() • Create wrapper to make easier to use – see basic-wrap.py • Server Side • Need either additional module or version 2.6 or later of Python • See example on next slide

  8. Python 2.6 ssl module server side example while True: newsocket, fromaddr = bindsocket.accept() connstream = ssl.wrap_socket(newsocket, server_side=True, certfile="mycertfile", keyfile="mykeyfile", ssl_version=ssl.PROTOCOL_TLSv1) deal_with_client(connstream)

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