Signing the Message, Sending It Back

All that is left, then, is for the server to “sign” the message — that is, to return the message's MIC (Message Integrity Code, a unique tag associated with message) to the client to prove that the message was sent and unwrapped successfully. To do that, the program uses the function gss_get_mic():

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maj_stat = gss_get_mic(&min_stat, context, GSS_C_QOP_DEFAULT,
                            &msg_buf, &xmit_buf);

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which looks at the message in msg_buf and produces the MIC from it, storing it in xmit_buf. The server then sends the MIC back to the client with send_token(), and the client verifies it with gss_verify_mic(). See Verifying the Message.

Finally, sign_server() performs some cleanup; it releases the GSS-API buffers msg_buf and xmit_buf with gss_release_buffer() and then destroys the context with gss_delete_sec_context().