CA design question?

[openssl-users@xxxxxxxxxxxx (Viktor Dukhovni)]

On Sat, Dec 05, 2015 at 07:55:50PM +0100, Walter H. wrote:

> my website has an official SSL certificate, which I renewed this year to
> have a SHA-256 certificate;
> when I test my site with SSLLabs.com, I'm shows two certificate paths:
> 
> the first one:
> my SSL cert (SHA-256) sent by server
> the intermediate (SHA-256) sent by server (SHA1 Fingerprint:
> 064969b7f4d6a74fd098be59d379fae429a906fb)
> the self-signed (SHA-256) in trust store (SHA1 Fingerprint:
> a3f1333fe242bfcfc5d14e8f394298406810d1a0)

All this obfuscation is rather pointless (and annoying), please
just post the certificates.  The last one above is:

    Certificate:
	Data:
	    Version: 3 (0x2)
	    Serial Number: 45 (0x2d)
	Signature Algorithm: sha256WithRSAEncryption
	    Issuer: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
	    Validity
		Not Before: Sep 17 19:46:37 2006 GMT
		Not After : Sep 17 19:46:36 2036 GMT
	    Subject: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
	    Subject Public Key Info:
		Public Key Algorithm: rsaEncryption
		    Public-Key: (4096 bit)
		    Modulus:
			...
		    Exponent: 65537 (0x10001)
	    X509v3 extensions:
		X509v3 Basic Constraints: critical
		    CA:TRUE
		X509v3 Key Usage: critical
		    Certificate Sign, CRL Sign
		X509v3 Subject Key Identifier: 
		    4E:0B:EF:1A:A4:40:5B:A5:17:69:87:30:CA:34:68:43:D0:41:AE:F2
		X509v3 Authority Key Identifier: 
		    keyid:4E:0B:EF:1A:A4:40:5B:A5:17:69:87:30:CA:34:68:43:D0:41:AE:F2
		X509v3 Certificate Policies: 
		    Policy: 1.3.6.1.4.1.23223.1.1.1
		      CPS: http://www.startssl.com/policy.pdf
		      CPS: http://www.startssl.com/intermediate.pdf
		      User Notice:
			Organization: Start Commercial (StartCom) Ltd.
			Number: 1
			Explicit Text: Limited Liability, read the section *Legal Limitations* of the StartCom Certification Authority Policy available at http://www.startssl.com/policy.pdf
		Netscape Cert Type: 
		    SSL CA, S/MIME CA, Object Signing CA
		Netscape Comment: 
		    StartCom Free SSL Certification Authority
	Signature Algorithm: sha256WithRSAEncryption
	     ...

> the second one:
> my SSL cert (SHA-256) sent by server
> the intermediate (SHA-256) sent by server (SHA1 Fingerprint:
> 064969b7f4d6a74fd098be59d379fae429a906fb)
> the self-signed (SHA-1) in trust store (SHA1 Fingerprint:
> 3e2bf7f2031b96f38ce6c4d8a85d3e2d58476a0f)

Here the last one is:

    Certificate:
	Data:
	    Version: 3 (0x2)
	    Serial Number: 1 (0x1)
	Signature Algorithm: sha1WithRSAEncryption
	    Issuer: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
	    Validity
		Not Before: Sep 17 19:46:36 2006 GMT
		Not After : Sep 17 19:46:36 2036 GMT
	    Subject: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
	    Subject Public Key Info:
		Public Key Algorithm: rsaEncryption
		    Public-Key: (4096 bit)
		    Modulus:
			...
		    Exponent: 65537 (0x10001)
	    X509v3 extensions:
		X509v3 Basic Constraints: 
		    CA:TRUE
		X509v3 Key Usage: 
		    Digital Signature, Key Encipherment, Key Agreement, Certificate Sign, CRL Sign
		X509v3 Subject Key Identifier: 
		    4E:0B:EF:1A:A4:40:5B:A5:17:69:87:30:CA:34:68:43:D0:41:AE:F2
		X509v3 CRL Distribution Points: 
		    Full Name:
		      URI:http://cert.startcom.org/sfsca-crl.crl
		    Full Name:
		      URI:http://crl.startcom.org/sfsca-crl.crl
		X509v3 Certificate Policies: 
		    Policy: 1.3.6.1.4.1.23223.1.1.1
		      CPS: http://cert.startcom.org/policy.pdf
		      CPS: http://cert.startcom.org/intermediate.pdf
		      User Notice:
			Organization: Start Commercial (StartCom) Ltd.
			Number: 1
			Explicit Text: Limited Liability, read the section *Legal Limitations* of the StartCom Certification Authority Policy available at http://cert.startcom.org/policy.pdf
		Netscape Cert Type: 
		    SSL CA, S/MIME CA, Object Signing CA
		Netscape Comment: 
		    StartCom Free SSL Certification Authority
	Signature Algorithm: sha1WithRSAEncryption
	     ...

Same subject, issuer and public key, different hash function in
the self signature.  Nothing up my sleeve.

  Issuer: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
 Subject: C=IL, O=StartCom Ltd., OU=Secure Digital Certificate Signing, CN=StartCom Certification Authority
 X509v3 Subject Key Identifier: 4E:0B:EF:1A:A4:40:5B:A5:17:69:87:30:CA:34:68:43:D0:41:AE:F2

> now my question how would it be possible to generate a SSL certificate that
> can be used with two different certificate paths?

There are two versions of one of the issuer certificates.

-- 
	Viktor.