Hi all,
In my setup (CentOS7, OpenLDAP 2.4.41 from the LDAP Tool Box project) I am using the following slapd.conf parameters for SSL-related configuration:
TLSProtocolMin 3.1
TLSCertificateFile /etc/pki/tls/certs/NNN.crt
TLSCertificateKeyFile /etc/pki/tls/private/NNN.key
TLSCACertificateFile /etc/pki/tls/certs/NNN.ca.pem
TLSDHParamFile /usr/local/openldap/etc/openldap/dh_2048.pem
TLSCipherSuite AESGCM:!RSA:!DSS:!ADH:!aECDH
The file /usr/local/openldap/etc/openldap/dh_2048.pem is a valid DH parameter file with size 2048:
<snip>
# openssl dh -in /usr/local/openldap/etc/openldap/dh_2048.pem -text -noout
PKCS#3 DH Parameters: (2048 bit)
prime:
</snip>
I am now testing the actual DH parameter size used during a TLS connection with instructions from https://bettercrypto.org/blog/2015/05/20/tls-logjam/ and it only shows DH parameter size 1024:
<snip>
$ echo | openssl s_client -connect alias01.alias.ooo:636 -cipher "EDH" 2>/dev/null
… much output …
No client certificate CA names sent
Peer signing digest: SHA512
Server Temp Key: DH, 1024 bits
</snip>
I was expecting "Server Temp Key: DH, 2048 bits”. Am I just testing this the wrong way or is there an issue with DH parameter configurations in OpenLDAP?
Thanks for any help!
jens
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