curl openssl can't verify IIS 7 self-signed cert even when added to curl-ca-bundle.crt

Question

I used IIS 7 on Windows Server Enterprise 2008 to generate a self-signed cert for use with IIS (basically one-click button).

However, even when I export and add this cert to a windows client's curl-ca-bundle.crt, neither it nor openssl.exe will not verify the cert correctly:

openssl s_client -CAfile curl-ca-bundle.crt -showcerts -connect myserver.ad.pri:443

CONNECTED(00000003)
depth=0 /CN=myserver.ad.pri
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 /CN=myserver.ad.pri
verify error:num=21:unable to verify the first certificate
verify return:1
---
Certificate chain
 0 s:/CN=myserver.ad.pri
   i:/CN=myserver.ad.pri
-----BEGIN CERTIFICATE-----
MIIDADCCAeigAwIBAgIQTi9gdBLdo6pJ1h4Zljr/wzANBgkqhkiG9w0BAQUFADAp
....
-----END CERTIFICATE-----
---
Server certificate
subject=/CN=myserver.ad.pri
issuer=/CN=myserver.ad.pri
---
No client certificate CA names sent
---
SSL handshake has read 924 bytes and written 444 bytes
---
New, TLSv1/SSLv3, Cipher is AES128-SHA
Server public key is 2048 bit
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : AES128-SHA
    Session-ID: 

    Session-ID-ctx:
    Master-Key: 
    Key-Arg   : None
    Start Time: 1377728216
    Timeout   : 300 (sec)
    Verify return code: 21 (unable to verify the first certificate)
---
read:errno=104

I used IE to export the cert to Base-64 Encoded, which is openssl-readable as PEM: openssl x509 -inform PEM -in myserver.crt -text

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            4e:2f:60:74:12:dd:a3:aa:49:d6:1e:19:96:3a:ff:c3
        Signature Algorithm: sha1WithRSAEncryption
        Issuer: CN=myserver.ad.pri
        Validity
            Not Before: Aug 26 15:38:46 2013 GMT
            Not After : Aug 26 00:00:00 2014 GMT
        Subject: CN=myserver.ad.pri
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
            RSA Public Key: (2048 bit)
                Modulus (2048 bit):
                    ....
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Key Usage:
                Key Encipherment, Data Encipherment
            X509v3 Extended Key Usage:
                TLS Web Server Authentication
    Signature Algorithm: sha1WithRSAEncryption
        ...
-----BEGIN CERTIFICATE-----
....

openssl/curl with the same curl-ca-bundle.crt will verify certs from google.com:443 etc. just fine.

Answer 1

I also ran into this (and I'm very surprised more people haven't.) when I couldn't get a NodeJS HTTP(s) client to connect to an IIS instance with a self-signed-certificate on it (one created through IIS manager) Just got the dreaded' unable to verify the first certificate error!

It seems that this is because the certificates that IISManager creates for this purpose specify some 'Key Usage' extensions; 'Key Encipherment' and 'Data Encipherment'.

It turns out that when openssl encounters a certificate that specifies 'Key Usage' but fails to specify the 'certSign' usage then the openssl code will discount that certificate as a possible CA certificate even if it has been correctly provided to the openssl code (meaning it is unable to verify the certificate against said absent CA!).

(See the logic here https://github.com/openssl/openssl/blob/6f0ac0e2f27d9240516edb9a23b7863e7ad02898/crypto/x509v3/v3_purp.c#L503 )

The solution is as the one already above, which is to create your own certificates with the correct key usages (or no key usage extensions!)

I also thought I should include an alternative way of creating the Self Signed certificate that openssl clients would be happy with if you're in windows land.

First download the powershell script from here

In a powershell console (Administrative) execute the following commands from within a folder that contains the downloaded scripts

New-SelfsignedCertificateEx -StoreLocation "LocalMachine" -KeyUsage "DigitalSignature,KeyEncipherment,KeyCertSign" -Subject "CN=<HOST_NAME_TO_USE>" -FriendlyName "<HOST_NAME_TO_USE>" -SignatureAlgorithm sha256 -SubjectAlternativeName "<HOST_NAME_TO_USE>","anotherhost.org","someotherdomain.com"

Once you've executed the above command your LocalMachine\Personal Certificates store will contain a self-signed certificate that can be used by IIS for its SSL communications. (Please note you may also need to copy this certificate into one of the Trusted Root stores as well to guarantee that the certificate is trusted on that machine)

Answer 2

I solved this by using openssl to create a self-signed CA cert, then created a server cert request (also in OpenSSL, for some reason openssl does not like to sign requests generated by IIS), signed it with the former CA cert, then exported to PKCS12. Then imported into IIS. Once the CA cert is added to curl-ca-bundle.crt, it will verify the chain correctly:

Generate a CA:

openssl req -new -x509 -days 3650 -extensions v3_ca \
-keyout cakey.pem -out cacert.pem -config /etc/ssl/openssl.cnf \
-newkey rsa:2048

Generate a server key and signing request:

openssl req -new -nodes -out server-csr.pem -keyout server-key.pem -newkey rsa:2048

Sign the request with the CA:

openssl ca -config /etc/ssl/openssl.cnf -cert cacert.pem -keyfile cakey.pem \
-out server-cert.pem -in server-csr.pem

Export the server cert to PKCS#12:

openssl pkcs12 -export -out server-key-cert.pfx \
-inkey server-key.pem -in server-cert.pem -certfile cacert.pem

Import server-key-cert.pfx into IIS. (Re)bind the site binding's SSL binding to the cert.

Append cacert.pem to clients' curl-ca-bundle.crt. openssl s_client -showcerts -CAfile curl-ca-bundle.crt -connect server:443 has depth 0 and 1 and will verify return.

Notes: Make sure that keyUsage = nonRepudiation, digitalSignature, keyEncipherment is enabled under section [usr_cert] in openssl.cnf else requests won't contain those keyUsage and IIS will complain on binding.