Zilog EZ80F91AZA User Manual download pdf (Page 40)

UM020107-1211 SSL Configuration

ZTP Network Security SSL Plug-In

User Manual

and MacSize fields. Lastly, the IsValid flag is set to TRUE so that this cipher suite can

be used for establishing a session.

Cipher Suite Tables

The first step in establishing an SSL session is for the client and server to determine a

common cipher suite. Both the client and server must be capable of supporting the exact

same cipher suite, or else the session will not be established. If the client supports only

TLS_RSA_WITH_RC4_128_MD5 and the server supports only

TLS_RSA_WITH_RC4_128_SHA, the client and server cannot establish an SSL session.

To facilitate the establishment of a session, it is advantageous if both parties are capable of

supporting multiple cipher suites. This type of support increases the chance that at least

one match will be found. With the ZTP Network Security SSL Plug-In, this task is accom-

plished by creating tables of

SSL_CS_INFO structures that define a set of cipher suites

supported by the SSL handshake protocols. Each implemented SSL handshake protocol

has a global variable, defined in

ssl_conf.c, that references its table of cipher suites.

These variables are named:

•

pSSL2_CipherSuites

•

pSSL3_CipherSuites

•

pTLS1_CipherSuites 

A second set of global variables specifies how many entries are present in each of the

cipher suite tables. These variables are named:

•

NumSSL2_CipherSuites

•

NumSSL3_CipherSuites

•

NumTLS1_CipherSuites

The following code fragment shows a sample cipher suite table for the TLSv1 handshake

protocol. For clarity, only the mnemonic of the

SSL_CS_INFO structure is shown, fol-

lowed by an ellipsis.

SSL_CS_INFO TLS1_CipherSuites[] =

{

{ TLS_NULL_WITH_NULL_NULL, ... },

{ TLS_RSA_WITH_RC4_128_MD5, ... },

{ TLS_RSA_WITH_DES_CBC_SHA, ... }

};

SSL_BYTE NumTLS1_CipherSuites =

sizeof(TLS1_CipherSuites) / sizeof(SSL_CS_INFO);

SSL_CS_INFO *pTLS1_CipherSuites = TLS1_CipherSuites;

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