61 lines
2 KiB
Markdown
61 lines
2 KiB
Markdown
### Server Name Indication
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Some TLS servers might want to provide service for various services,
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all on the same port, but with different names. The SNI extension
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allows a client to request a specific server name. The server may use
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the requested server name to select the X.509 certificate chain which
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it presents to the client.
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### Configuration interface
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A user provides a full certificate chain and a private key
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corresponding to the first certificate in the list to OCaml-TLS,
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captured by the type `certchain`.
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````
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type certchain = Certificate.certificate list * Nocrypto.Rsa.priv
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````
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The `own_cert` polymorphic variant covers the various configuration
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options: either no certificate is provided, a single one, multiple
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ones (whose common name/subject alternative name are used for
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disambiguation), and multiple with a default one.
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````
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type own_cert = [
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| `None
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| `Single of certchain
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| `Multiple of certchain list
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| `Multiple_default of certchain * certchain list
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]
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````
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### Validation
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The configuration of certificates is intertwined with ciphersuites:
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each ciphersuite which requires a certificate furthermore depends on
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properties of this certificate - RSA and DHE_RSA require the key to be
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RSA, RSA requires the X.509v3 extension key_usage to contain
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encipherment, DHE_RSA requires key_usage to contain digital_signature.
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There must exist at least one certificate with the mentioned
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properties for each configured ciphersuite.
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Furthermore, to avoid ambiguity, the hostnames in ``Multiple` and
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``Multiple_default` certificate lists must be non-overlapping.
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### Certificate selection
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If the server is configured with only a default certificate, this is
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always used.
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If the client does not request for a server name, the default
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certificate is used.
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If the client requests a specific server name:
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- find a strict match
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- find a wildcard match
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- use the default one if present
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Only after a certificate is set for the session, the ciphersuite is
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selected, depending on the properties of the certificate.
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