For the most up-to-date information on Apache and SNI, including additional HTTP-Specific RFCs, please refer to the Apache Wiki
FYsI: "Multiple (different) SSL certificates on one IP" is brought to you by the magic of TLS Upgrading.
It works with newer Apache servers (2.2.x) and reasonably recent browsers (don't know versions off the top of my head).
RFC 2817 (upgrading to TLS within HTTP/1.1) has the gory details, but basically it works for a lot of people (if not the majority).
You can reproduce the old funky behavior with openssl's s_client command (or any "old enough" browser) though.
Edit to add: apparently curl can show you what's happening here better than openssl:
SSLv3
mikeg@flexo% curl -v -v -v -3 https://www.yummyskin.com
* About to connect() to www.yummyskin.com port 443 (#0)
* Trying 69.164.214.79... connected
* Connected to www.yummyskin.com (69.164.214.79) port 443 (#0)
* successfully set certificate verify locations:
* CAfile: /usr/local/share/certs/ca-root-nss.crt
CApath: none
* SSLv3, TLS handshake, Client hello (1):
* SSLv3, TLS handshake, Server hello (2):
* SSLv3, TLS handshake, CERT (11):
* SSLv3, TLS handshake, Server key exchange (12):
* SSLv3, TLS handshake, Server finished (14):
* SSLv3, TLS handshake, Client key exchange (16):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSL connection using DHE-RSA-AES256-SHA
* Server certificate:
* subject: serialNumber=wq8O9mhOSp9fY9JcmaJUrFNWWrANURzJ; C=CA;
O=staging.bossystem.org; OU=GT07932874;
OU=See www.rapidssl.com/resources/cps (c)10;
OU=Domain Control Validated - RapidSSL(R);
CN=staging.bossystem.org
* start date: 2010-02-03 18:53:53 GMT
* expire date: 2011-02-06 13:21:08 GMT
* SSL: certificate subject name 'staging.bossystem.org'
does not match target host name 'www.yummyskin.com'
* Closing connection #0
* SSLv3, TLS alert, Client hello (1):
curl: (51) SSL: certificate subject name 'staging.bossystem.org'
does not match target host name 'www.yummyskin.com'
TLSv1
mikeg@flexo% curl -v -v -v -1 https://www.yummyskin.com
* About to connect() to www.yummyskin.com port 443 (#0)
* Trying 69.164.214.79... connected
* Connected to www.yummyskin.com (69.164.214.79) port 443 (#0)
* successfully set certificate verify locations:
* CAfile: /usr/local/share/certs/ca-root-nss.crt
CApath: none
* SSLv3, TLS handshake, Client hello (1):
* SSLv3, TLS handshake, Server hello (2):
* SSLv3, TLS handshake, CERT (11):
* SSLv3, TLS handshake, Server key exchange (12):
* SSLv3, TLS handshake, Server finished (14):
* SSLv3, TLS handshake, Client key exchange (16):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSL connection using DHE-RSA-AES256-SHA
* Server certificate:
* subject: C=CA; O=www.yummyskin.com; OU=GT13670640;
OU=See www.rapidssl.com/resources/cps (c)09;
OU=Domain Control Validated - RapidSSL(R);
CN=www.yummyskin.com
* start date: 2009-04-24 15:48:15 GMT
* expire date: 2010-04-25 15:48:15 GMT
* common name: www.yummyskin.com (matched)
* issuer: C=US; O=Equifax Secure Inc.; CN=Equifax Secure Global eBusiness CA-1
* SSL certificate verify ok.
Best Answer
SSL uses several encrypt algorithmic at different points.
Typically it will use a asymmetric cryptography authenticate the hosts and establish trust between the client and server. Then a random key will be generated and shared between the hosts and a symmetric cryptography algorthim will be used for the actual payload.
Typically the asymmetric key will be RSA with key sizes of 1024, 2048, or 4096. The key size doesn't really affect the symmetric that is used for the payload. These days most certificate vendors will sign a 2048 or 4096 certificate request, key sizes of 1024 are pretty weak. While most CA keys are 2048 bits, many will sign larger keys, so you don't have to limit your private key to 2048 bits.
The symmetric algorithim that is used will depend on the client and server. The client and server will select the most secure option available. If you are using apache then you use the
SSLCipherSuiteto select which symmetric ciphers you will permit.Asymmetric cryptography is has the large sizes of the keys(2048,4096), and it is very slow. That is why it is only used during the initial phase. Once the connection is established, communication happens over the relatively fast symmetric cryptography which uses the smaller key sizes (128,256).