[openssl-users] How to form a proper hash after writing something into SSL handshake.(Revised)

Sai Teja Chowdary asteja.chowdary.ece13 at iitbhu.ac.in
Sat Dec 30 03:18:16 UTC 2017

Hi everyone,

I want to send client certificate, client key exchange and client verify in
a single handshake message which appears as multiple handshake messages in
a single record. But to sent the client verify I need to first make a hash
of previous messages(client certificate and client key exchange) to create
the signature. I tried framing the record with above three messages and
then directly sending the record in the wire using SSL3_write_machine()
which is giving me Bad signature error. So i thought of doing a hash of
client certificate and client key exchange messages that go before client

Can anyone help me to find the function in OpenSSL 1.1.1-dev  xx XXX xxxx
(or right procedure that needs to be done before creating a certificate
verify message)that can do a proper transcript(digest or hash not clear). I
tried using ssl3_finish_mac() on the message containing client certificate
and client key exchange and then tried to generate the signature in
certificate verify message.

But it is giving me a digest check error. I am new to the mailing list want
a bit of help to proceed forward stuck here. Please reply in case if
anything is not clear.

Here is a code snippet, how I am forming the data containing all client
certificate , client key exchange and certificate verify messages inside

*if(WPACKET_init(&pkt, s->init_buf)){*
*//Client certificate formation*
*             if(!ssl_set_handshake_header(s,&pkt,mt) || confunc != NULL &&
!confunc(s,&pkt) ||         !ssl_close_construct_packet(s,&pkt,mt)){*
*                  printf("PROBLEM 1\n");*
*                }*
*             transition(s);  //transition to next state i.e client key
*             get_construct_message_f(s, &pkt, &confunc, &mt);*
*//client key exchange formation*
*             if(!ssl_set_handshake_header(s,&pkt,mt) || confunc != NULL &&
!confunc(s,&pkt) ||         !ssl_close_construct_packet(s,&pkt,mt)){*
*                   printf("PROBLEM 2\n");*
*                }*
*//ssl3_finish_mac(s, &s->init_buf->data[s->init_off], s->init_num);*
*             st->write_state_work = post_work(s, st->write_state_work);*
*             transition(s);  // transition to next state i.e  certificate
*             get_construct_message_f(s, &pkt, &confunc, &mt);*
*//certificate verify message formation.*
*             if(!ssl_set_handshake_header(s,&pkt,mt) || confunc != NULL &&
!confunc(s,&pkt) ||
*                   printf("PROBLEM 3\n");*
*                }*
*             WPACKET_finish(&pkt);*

I also tried to do a ssl3_finish_mac() individually after forming Client
certificate and client key exchange (this part is not there in the code but
that way also gave me digest check error.)

Here is the stackoverflow link that i posted the question in. Take a look
at it for the trace snapshot for handshake message that I am trying to form.

Please take a look at it, appreciate every bit of help.

Jordan, thanks for the suggestion i will definitely try to state the error
now on. I am not sure whether SSL_get_error() logs these errors, i tried to
print SSL_get_error() it is returning NULL.

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