Can I build a DH public key from an OpenSSL configuration file?

Yes, you can build a DH public key from an OpenSSL configuration file, if you know the components of the key, as shown in the test below:

C:\Users\fyicenter>type asn1_dh_pub_key.cnf
asn1 = SEQUENCE:dh_pri_key

[dh_pri_key]
algorithm  =SEQUENCE:dh_alg
private    =BITWRAP,INTEGER:0x4CC9C94CEB5B13F2B4B3ABB9F20CB830FFC3BB5DC6\
428C08B18CF3E5301908AD

[dh_alg]
algorithm =OID:dhKeyAgreement
parameter =SEQUENCE:dh_param

[dh_param]
prime      =INTEGER:0x8B58E1395DF5CF48DA87B088C6525EFF4AECBDA5C269EF2378\
A31A4A62B1647B
generator  =INTEGER:0x02

C:\Users\fyicenter>\local\openssl\openssl asn1parse -
genconf asn1_dh_pub_key.cnf -noout -out dh_pub_key.der

C:\Users\fyicenter>\local\openssl\openssl pkey -pubin
 -in dh_pub_key.der -inform DER -text -noout
DH Public-Key: (256 bit)
    public-key:
        4c:c9:c9:4c:eb:5b:13:f2:b4:b3:ab:b9:f2:0c:b8:
        30:ff:c3:bb:5d:c6:42:8c:08:b1:8c:f3:e5:30:19:
        08:ad
    prime:
        00:8b:58:e1:39:5d:f5:cf:48:da:87:b0:88:c6:52:
        5e:ff:4a:ec:bd:a5:c2:69:ef:23:78:a3:1a:4a:62:
        b1:64:7b
    generator: 2 (0x2)

⇒ Other OpenSSL Versions for Windows

⇐ OpenSSL "ans1parse" - DH Public Key in ASN.1 Structure

⇑ OpenSSL "ans1parse" Command

⇑⇑ OpenSSL Tutorials