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After upgrade CA XCOM server OS from RHEL 6.9 to 7.7, secure socket ping fails with XCOMU0298E and XCOMU0780E handshake failure


Article ID: 186759


Updated On:


XCOM Data Transport XCOM Data Transport - Linux PC


Linux servers that were previously running Linux 6.9 (Santiago) were upgraded to RHEL 7.7 (Maipo).
After the upgrade testing from the RHEL 7.7 source XCOM server to a RHEL 6.10 target XCOM server with command "xcomtcp -ping" on secure socket (8045) shows SSL handshake error as follows:

RHEL 7.7 source:
XCOMU0298E Unable to allocate remote transaction program: Txpi  215: Socket send error return value = 9

RHEL 6.10 target:
The $XCOM_HOME/xcom.log file contains this corresponding error:
XCOMU0780E Txpi  308: TxpiInitSSL Failed msg = <error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure
+++ SSL alert number 40> value = 0:


Release : 11.6 SP01 17021
Component : CA XCOM Data Transport for Linux PC


XCOM support not able to recreate "xcomtcp -ping" problem from RHEL 7.7 to RHEL 6.10 and advised to run the "xcomtcp -ping" command with trace options "-t" and "XTRACE=10" as follows:
# xcomtcp -ping -t REMOTE_SYSTEM=xxx PORT=8045 TRNENCRL_CIPHER=ALL SECURE_SOCKET=YES XTRACE=10 > xcom_ping.out 2>&1
The resulting xcom_ping.out file showed these errors:
E - catoossl.c(2899): Error 308

E -catoossl.c(2899): Txpi  308: TxpiInitSSL Failed msg = <error:1408D177:SSL routines:ssl3_get_key_exchange:bad dh g value> value = 4294967295

Running openssl command "openssl s_client -connect target_server:8045 -showcerts -status" to the target server also showed error "ssl3_get_key_exchange:bad dh g value" and "Cipher is (NONE)"
XCOM Support observed the same result using openssl command from RHEL 7.7 to RHEL 6.10:
"openssl s_client -connect target_server:8045 -showcerts -status -msg"
"-msg" shows each step of the handshake sequence and the "bad dh g value" error occurs after the server key exchange step:

NOTE: XCOM uses its own CAPKI SSL libraries and not the system openssl libraries.

On the target server, which is effectively the SSL server, the configssl.cnf file [RSAKEY] parameter "RECEIVE_SIDE" controls whether RSA or Diffie Hellman (DH) key exchange is used by XCOM as follows:
1. The OOTB default value for [RSAKEY] parameter "RECEIVE_SIDE" is "NO" which means Diffie Hellman key exchange will be used by the XCOM receiver/target server and the resulting cipher observed by XCOM support in their trace file was DHE-RSA-AES256-SHA. For the reported problems "RECEIVE_SIDE = NO" was being used.
2. When [RSAKEY] parameter "RECEIVE_SIDE" is changed to "YES" it means an RSA key exchange will be used by the XCOM receiver/target server and the resulting cipher observed by XCOM support in their trace file was AES256-SHA. After the option "RECEIVE_SIDE = YES" was implemented it resolved both the "xcomtcp -ping" and openssl errors. Therefore it appears that the RHEL 7.7 upgrade had somehow introduced a problem which prevented use of the Diffie Hellman key exchange that did not exist before. Additional investigation using [RSAKEY] parameter "RECEIVE_SIDE = NO" found that DH could be used successfully for both "xcomtcp -ping" and openssl tests if a prime of 1024 instead of the default 256 was used 

So the 2 possible resolutions for target server config.ssl.cnf file are:
1. Set [RSAKEY] parameter RECEIVE_SIDE to YES so that RSA key exchange is used i.e.

2. Set [RSAKEY] parameter RECEIVE_SIDE to NO so that DH key exchange is used and also use a DH prime of 1024 i.e.


# Optional (for RSA NO, see above). If RSA NO and DH files empty,
#  then internal program tables will be used.
# DH_512_RECEIVE_SIDE  = /opt/CA/XCOM/config/dh512.pem
DH_1024_RECEIVE_SIDE = /opt/CA/XCOM/config/dh1024.pem
# DH_2048_RECEIVE_SIDE = /opt/CA/XCOM/config/dh2048.pem
# DH_4096_RECEIVE_SIDE = /opt/CA/XCOM/config/dh4096.pem

However as RSA is more secure than DH it is normally advised to use the RSA option.

Additional Information

CA XCOM SSL - How to set up RSA or Diffie Hellman (DH) for key exchange in file configssl.cnf