OpenSSL: how to setup an OCSP server for checking third-party certificates?

In case you are interested: here's my solution.

First I ditched OpenSSL's OCSP responder. It can't be used for certificates that have not been created with your self-signed CA.

Then I used the OpenCA libraries to create a command line utility that is capable of creating an OCSP response from an OSCP request. It works entirely file-based: you run it with a DER formatted OSCP request as input file, and it outputs a DER formatted OCSP response file.

A second argument to the command line utility is the revocation status: good, revoked or unknown. The certificate status in the response file will be the same as the passed argument. The code is based on this sample, pointed out to me by The Rook in this post.

The final step was to create a HTTP server that builds upon the command line utility. I used Ruby's Merb framework for that. A nifty feature is that the revocation status can be requested as a HTTP url, for example: http://127.0.0.1:5000/good.

Update

Since above links are broken I'll post the script contents here:

AllCommands.sh:

#################
# Create the CA #
#################

# Create folder stucture and default files
mkdir -p CA/private
mkdir -p CA/newcerts
touch CA/index.txt
echo "00" >> CA/serial

# Create the CA 
openssl req -new -x509 -keyout ./CA/private/cakey.pem -out ./CA/cacert.pem -days 365 -passin pass:secret1 -passout pass:secret1 -config openssl.cnf


##############################
# Create a test certificate  #
##############################

# Create the request
openssl req -batch -config ./openssl.cnf -new -keyout test-certificate.key -out test-certificate.request -days 365 -passin pass:secret1 -passout pass:secret1 

# Create the certificate 
openssl ca -batch -config ./openssl.cnf -policy policy_anything -passin pass:secret1 -out test-certificate.pem -infiles test-certificate.request

# Cleanup request file
rm test-certificate.request

echo "test-certificate.pem has been generated."

##################################
# Sign a third party certificate #
##################################

# Create a key
openssl genrsa -des3 -passout pass:secret1 -out tmp.key 1024

# Remove the password from the key
cp tmp.key tmp.key.old
openssl rsa -in tmp.key.old -passin pass:secret1 -passout pass:secret1 -out tmp.key
rm tmp.key.old

# Sign the certificate with this key
openssl x509 -days 365 -in thirdparty.pem -signkey tmp.key -passin pass:secret1 -text -out thirdparty-signed.pem

# Remove tempfile
rm tmp.key


########################################
# Add the signed certificate to the CA #
########################################

# Create the certs dir if it doesn't already exist
mkdir -p CA/certs

# Copy our signed third party certificate
cp thirdparty-signed.pem CA/certs

# Create the hash-link
cd CA/certs
ln -s thirdparty-signed.pem `openssl x509 -hash -noout -in thirdparty-signed.pem`.0
cd -


#################################################
# Add the signed certificate to the CA database #
#################################################

openssl ca -config openssl.cnf -policy policy_anything -passin pass:secret1 -ss_cert thirdparty-signed.pem


####################
# Start the server #
####################

# Use test-certificate.pem as response signer.
openssl ocsp -CApath ./CA/certs -index CA/index.txt -port 5000 -rkey test-certificate.key -rsigner test-certificate.pem -CA CA/cacert.pem -text

# The client request:
# $ openssl ocsp -issuer CA/cacert.pem -VAfile test-certificate.pem -cert thirdparty.pem -url http://10.5.5.247:5000
# => Response verify OK
# => thirdparty.pem: unknown
#        This Update: Apr 13 13:00:59 2010 GMT

openssl.cnf:

#
# OpenSSL example configuration file.
# This is mostly being used for generation of certificate requests.
#

# This definition stops the following lines choking if HOME isn't
# defined.
HOME = $ENV::HOME
RANDFILE= $ENV::HOME/.rnd

# Extra OBJECT IDENTIFIER info:
#oid_file= $ENV::HOME/.oid
oid_section= new_oids

# To use this configuration file with the "-extfile" option of the
# "openssl x509" utility, name here the section containing the
# X.509v3 extensions to use:
# extensions= 
# (Alternatively, use a configuration file that has only
# X.509v3 extensions in its main [= default] section.)

[ new_oids ]

# We can add new OIDs in here for use by 'ca' and 'req'.
# Add a simple OID like this:
# testoid1=1.2.3.4
# Or use config file substitution like this:
# testoid2=${testoid1}.5.6

####################################################################
[ ca ]
default_ca = CA_default # The default ca section

####################################################################
[ CA_default ]

dir                   = ./CA # Where everything is kept
certs                 = $dir/certs # Where the issued certs are kept
crl_dir               = $dir/crl # Where the issued crl are kept
database              = $dir/index.txt # database index file.
new_certs_dir         = $dir/newcerts# default place for new certs.

certificate           = $dir/cacert.pem # The CA certificate
serial                = $dir/serial # The current serial number
crlnumber             = $dir/crlnumber # the current crl number

 # must be commented out to leave a V1 CRL
crl                   = $dir/crl.pem# The current CRL
private_key           = $dir/private/cakey.pem # The private key
RANDFILE              = $dir/private/.rand # private random number file

x509_extensions       = usr_cert # The extentions to add to the cert

# Comment out the following two lines for the "traditional"
# (and highly broken) format.
name_opt              = ca_default # Subject Name options
cert_opt              = ca_default # Certificate field options

# Extension copying option: use with caution.
# copy_extensions = copy

# Extensions to add to a CRL. Note: Netscape communicator chokes on V2 CRLs
# so this is commented out by default to leave a V1 CRL.
# crlnumber must also be commented out to leave a V1 CRL.
# crl_extensions = crl_ext

default_days = 365 # how long to certify for
default_crl_days = 30 # how long before next CRL
default_md = sha1 # which md to use.
preserve = no # keep passed DN ordering

# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy = policy_match

# For the CA policy
[ policy_match ]
countryName = match
stateOrProvinceName = match
organizationName = match
organizationalUnitName = optional
commonName = supplied
emailAddress = optional

# For the 'anything' policy
# At this point in time, you must list all acceptable 'object'
# types.
[ policy_anything ]
countryName = optional
stateOrProvinceName = optional
localityName = optional
organizationName = optional
organizationalUnitName = optional
commonName = supplied
emailAddress = optional

####################################################################
[ req ]
default_bits = 1024
default_keyfile = privkey.pem
distinguished_name = req_distinguished_name
prompt = no
attributes = req_attributes
x509_extensions = v3_ca # The extentions to add to the self signed cert

# Passwords for private keys if not present they will be prompted for
# input_password = secret
# output_password = secret

# This sets a mask for permitted string types. There are several options. 
# default: PrintableString, T61String, BMPString.
# pkix: PrintableString, BMPString.
# utf8only: only UTF8Strings.
# nombstr : PrintableString, T61String (no BMPStrings or UTF8Strings).
# MASK:XXXX a literal mask value.
# WARNING: current versions of Netscape crash on BMPStrings or UTF8Strings
# so use this option with caution!
string_mask = nombstr

# req_extensions = v3_req # The extensions to add to a certificate request


[ req_attributes ]
challengePassword = A challenge password

[ req_distinguished_name ]
C=DE
ST=Oost-Vlaanderen
L=Gent
O=Corp
OU=Testing Team
CN=johnsmith
[email protected]

[ usr_cert ]

# These extensions are added when 'ca' signs a request.

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:TRUE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy
# An alternative to produce certificates that aren't
# deprecated according to PKIX.
# subjectAltName=email:move

# Copy subject details
# issuerAltName=issuer:copy

#nsCaRevocationUrl= http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

[ v3_req ]

# Extensions to add to a certificate request

basicConstraints = CA:TRUE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment

[ v3_ca ]


# Extensions for a typical CA


# PKIX recommendation.

subjectKeyIdentifier=hash

authorityKeyIdentifier=keyid:always,issuer:always

# This is what PKIX recommends but some broken software chokes on critical
# extensions.
#basicConstraints = critical,CA:true
# So we do this instead.
basicConstraints = CA:true

# Key usage: this is typical for a CA certificate. However since it will
# prevent it being used as an test self-signed certificate it is best
# left out by default.
# keyUsage = cRLSign, keyCertSign

# Some might want this also
# nsCertType = sslCA, emailCA

# Include email address in subject alt name: another PKIX recommendation
# subjectAltName=email:copy
# Copy issuer details
# issuerAltName=issuer:copy

# DER hex encoding of an extension: beware experts only!
# obj=DER:02:03
# Where 'obj' is a standard or added object
# You can even override a supported extension:
# basicConstraints= critical, DER:30:03:01:01:FF

[ crl_ext ]

# CRL extensions.
# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always,issuer:always

[ proxy_cert_ext ]
# These extensions should be added when creating a proxy certificate

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer:always

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy
# An alternative to produce certificates that aren't
# deprecated according to PKIX.
# subjectAltName=email:move

# Copy subject details
# issuerAltName=issuer:copy

#nsCaRevocationUrl= http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

# This really needs to be in place for it to be a proxy certificate.
proxyCertInfo=critical,language:id-ppl-anyLanguage,pathlen:3,policy:foo

[ my_v3_ext ]
basicConstraints = CA:true

thirdparty.pem:

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            d9:6f:db:ad:33:69:ce:63
        Signature Algorithm: sha1WithRSAEncryption
        Issuer: C=DE, ST=Berlin, L=Berlin, O=AVM GmbH, OU=Euro-DOCSIS, OU=Germany, CN=AVM GmbH Cable Modem Root Certificate Authority
        Validity
            Not Before: Jan 20 13:28:06 2010 GMT
            Not After : Jun  7 13:28:06 2037 GMT
        Subject: C=DE, O=AVM GmbH, OU=Euro-DOCSIS, CN=00:04:0E:C4:AE:94
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
            RSA Public Key: (1024 bit)
                Modulus (1024 bit):
                    00:d5:73:b6:23:c6:23:ff:97:25:84:21:b7:25:f1:
                    8f:f7:c1:ae:dc:13:ea:56:69:c1:f4:9c:74:d7:b8:
                    50:74:2b:0b:4c:56:0f:ab:8e:b3:8e:04:26:74:e6:
                    7c:8d:23:2e:34:74:6c:cc:d6:d6:81:b1:ba:1a:ed:
                    80:fa:fd:c5:65:09:23:5e:6d:b9:15:9e:52:9f:d2:
                    66:f7:3d:b9:4b:2b:ef:ab:80:72:26:47:24:17:35:
                    c9:2a:c7:df:53:a6:15:c0:f4:b7:bc:40:37:29:51:
                    c5:50:9a:90:d8:af:56:42:9a:07:3c:8c:77:f0:93:
                    09:c8:0b:52:7a:3d:64:5f:d9
                Exponent: 65537 (0x10001)
    Signature Algorithm: sha1WithRSAEncryption
        27:64:a3:d5:76:d2:86:32:6e:c0:e5:45:39:1f:2a:1a:04:d9:
        46:d9:92:ee:71:a1:7d:07:77:ac:1a:0f:2a:e2:a1:3c:d2:aa:
        13:e2:df:55:6a:3c:93:54:e4:63:b8:5d:3c:6b:97:3b:b2:2e:
        e6:c0:17:6c:6b:e2:0c:ea:66:48:42:02:f3:41:d2:cc:ca:ed:
        64:a6:b9:78:97:b3:df:87:75:61:fb:86:49:18:03:86:7c:4c:
        89:cc:ba:6b:6d:ad:6c:4b:da:ad:1c:65:b8:42:9d:ad:c5:b1:
        35:60:36:b4:e2:1f:a3:c9:74:e4:34:3a:b5:d2:d6:1c:80:97:
        4d:8f:b3:ab:c4:35:95:c4:ca:e5:93:2b:dc:36:54:51:04:d3:
        ea:34:c6:2f:7b:fd:7e:24:04:35:9d:c2:6b:59:e0:ef:dc:0e:
        6b:27:96:d3:9c:63:87:4d:c3:17:b6:4b:24:39:25:08:4e:d8:
        0e:14:8f:a9:8d:63:ff:74:d3:62:de:d7:11:71:e6:fd:fc:94:
        0d:77:27:9f:a3:e5:4c:84:9b:7a:d0:4b:6e:ba:b6:d5:35:9b:
        97:2f:c4:ff:b9:6b:fa:de:50:2f:38:12:4f:40:2c:55:8c:e7:
        db:42:fc:df:f9:65:74:52:81:42:b0:88:c8:9b:0f:9b:09:93:
        de:ae:e1:19
-----BEGIN CERTIFICATE-----
MIIC9DCCAdygAwIBAgIJANlv260zac5jMA0GCSqGSIb3DQEBBQUAMIGkMQswCQYD
VQQGEwJERTEPMA0GA1UECBMGQmVybGluMQ8wDQYDVQQHEwZCZXJsaW4xETAPBgNV
BAoTCEFWTSBHbWJIMRQwEgYDVQQLEwtFdXJvLURPQ1NJUzEQMA4GA1UECxMHR2Vy
bWFueTE4MDYGA1UEAxMvQVZNIEdtYkggQ2FibGUgTW9kZW0gUm9vdCBDZXJ0aWZp
Y2F0ZSBBdXRob3JpdHkwHhcNMTAwMTIwMTMyODA2WhcNMzcwNjA3MTMyODA2WjBS
MQswCQYDVQQGEwJERTERMA8GA1UEChMIQVZNIEdtYkgxFDASBgNVBAsTC0V1cm8t
RE9DU0lTMRowGAYDVQQDExEwMDowNDowRTpDNDpBRTo5NDCBnzANBgkqhkiG9w0B
AQEFAAOBjQAwgYkCgYEA1XO2I8Yj/5clhCG3JfGP98Gu3BPqVmnB9Jx017hQdCsL
TFYPq46zjgQmdOZ8jSMuNHRszNbWgbG6Gu2A+v3FZQkjXm25FZ5Sn9Jm9z25Syvv
q4ByJkckFzXJKsffU6YVwPS3vEA3KVHFUJqQ2K9WQpoHPIx38JMJyAtSej1kX9kC
AwEAATANBgkqhkiG9w0BAQUFAAOCAQEAJ2Sj1XbShjJuwOVFOR8qGgTZRtmS7nGh
fQd3rBoPKuKhPNKqE+LfVWo8k1TkY7hdPGuXO7Iu5sAXbGviDOpmSEIC80HSzMrt
ZKa5eJez34d1YfuGSRgDhnxMicy6a22tbEvarRxluEKdrcWxNWA2tOIfo8l05DQ6
tdLWHICXTY+zq8Q1lcTK5ZMr3DZUUQTT6jTGL3v9fiQENZ3Ca1ng79wOayeW05xj
h03DF7ZLJDklCE7YDhSPqY1j/3TTYt7XEXHm/fyUDXcnn6PlTISbetBLbrq21TWb
ly/E/7lr+t5QLzgST0AsVYzn20L83/lldFKBQrCIyJsPmwmT3q7hGQ==
-----END CERTIFICATE-----

The command line utility using OpenCA libraries is written in C:

#include <libpki/pki.h>


PKI_X509_OCSP_REQ * CreateOCSPRequest(PKI_X509_CERT * cacert, long long serial)
{
    PKI_X509_OCSP_REQ *request = NULL;

    request = PKI_X509_OCSP_REQ_new();
    if (request == NULL )
    {
         printf("Memory Errorequest!");
         exit(1);
    }   

    // Adds the details about certificate (serial issued by cacert)
    if (PKI_X509_OCSP_REQ_add_longlong( request, serial, cacert, NULL) == PKI_ERR)
    {
         printf ("Can not add serial!");
         exit (1);
    }

    if (PKI_X509_OCSP_REQ_add_nonce(request, 0) == PKI_ERR )
    {
         printf ("Can not add NONCE to REQUEST!");
         exit(1);
    }   
    return request;
}


PKI_X509_OCSP_RESP * CreateOCSPResponse(PKI_X509_OCSP_REQ *request, PKI_OCSP_CERTSTATUS ocspStatus)
{   
    PKI_X509_OCSP_RESP * resp = NULL;
    PKI_OCSP_CERTID *cid = NULL;

    // Create a new OCSP response
    if ((resp = PKI_X509_OCSP_RESP_new()) == NULL)
    {
         printf("Memory allocation errorequest!\n");
         exit (1);
    }

    // Now, let's set the status of the response
    if (PKI_X509_OCSP_RESP_set_status(resp, PKI_X509_OCSP_RESP_STATUS_SUCCESSFUL) == PKI_ERR)
    {
        printf("ERROR: setting response status failed.\n");
        exit (1);
    }
    printf ("Set response status.\n");

    // We now want to copy the NONCE from the request...
    if (PKI_X509_OCSP_RESP_copy_nonce(resp, request) == PKI_ERR)
    {
        printf("ERROR::can not copy NONCE!!!\n");
        exit (1);
    }
    printf ("Added NONCE.\n");

    // We also need the Certificate Identifier from the request
    if ((cid = PKI_X509_OCSP_REQ_get_cid(request, 0)) == NULL)
    {
        printf("Can not get CID from request!\n");
        exit (1);
    }

    // Let's add the status of the requested certificate to the response
    int ret = PKI_ERR;
    if (ocspStatus == PKI_OCSP_CERTSTATUS_REVOKED)
    {
        PKI_TIME * revocationTime = PKI_TIME_new(0);
        PKI_TIME * thisUpdate = PKI_TIME_new(100);
        PKI_TIME * nextUpdate = PKI_TIME_new(200);
        ret = PKI_X509_OCSP_RESP_add(resp, cid, ocspStatus, revocationTime, thisUpdate, nextUpdate, CRL_REASON_KEY_COMPROMISE, NULL);   
        PKI_TIME_free(revocationTime);
        PKI_TIME_free(thisUpdate);
        PKI_TIME_free(nextUpdate);
    }
    else
    {
        ret = PKI_X509_OCSP_RESP_add(resp, cid, ocspStatus, NULL, NULL, NULL, CRL_REASON_UNSPECIFIED, NULL);
    }

    if (ret == PKI_ERR)
    {
        printf("Add CID to response failed!\n");
        exit (1);
    }
    printf ("Added CID.\n");
    return resp;
}


PKI_X509_CERT * ReadCertificate(char * file)
{
    PKI_X509_CERT * cert = NULL;
    if ((cert = PKI_X509_CERT_get(file, NULL, NULL)) == NULL)
    {
        printf("Failed to load certificate: %s\n", file);
        exit(1);
    }
    return cert;
}


void SignResponse(PKI_X509_OCSP_RESP * resp)
{
    PKI_X509_KEYPAIR * keyPair = PKI_X509_KEYPAIR_get("root.key", NULL, NULL);
    if (!keyPair)
    {
        printf("Obtaining keypair from root.key failed!");
        exit (1);
    }

    PKI_X509_CERT * caCertificate = ReadCertificate("CA/cacert.pem");
    PKI_X509_CERT * signerCertificate = ReadCertificate("root.pem");    
    PKI_X509_OCSP_RESP_sign(resp, keyPair, signerCertificate, caCertificate, NULL, NULL);
}


void genresponse(PKI_OCSP_CERTSTATUS ocspStatus)
{   
    PKI_X509_OCSP_REQ *request = NULL;
    PKI_X509_OCSP_RESP * resp = NULL;
    PKI_X509_CERT * cacert = NULL;
    PKI_TOKEN * tk = NULL;

    if ((request = PKI_X509_OCSP_REQ_get("req.der", NULL, NULL)) == NULL)
    {
        printf("ERROR, can't load req.der!\n");
        exit(1);
    }
    resp = CreateOCSPResponse(request, ocspStatus);

    // Now sign the response
    SignResponse(resp);
    printf("Response has been signed.\n");

    PKI_X509_OCSP_RESP_put(resp, PKI_DATA_FORMAT_ASN1, "resp.der", NULL, NULL, NULL);
    printf("Response file resp.der has been written.\n");
}


void genrequest(long long serial)
{
    PKI_X509_OCSP_REQ *request = NULL;
    PKI_X509_OCSP_RESP * resp = NULL;
    PKI_X509_CERT * cacert = NULL;

    if ((cacert = PKI_X509_CERT_get("cacert.pem", NULL, NULL)) == NULL)
    {
         printf("ERROR, can not load cacert.pem!\n");
         exit(1);
    }

    request = CreateOCSPRequest(cacert, serial);
    PKI_X509_OCSP_REQ_put(request, PKI_DATA_FORMAT_ASN1, "req.der", NULL, NULL, NULL);
    printf("req.der written.\n");

}


void PrintUsage()
{
    printf("Usage: ocsp { genrequest <serial> | genresponse <good | revoked | unknown> } \n");
}


/**
 * Main function
 * 
 */
int main(int argc, char** argv)
{
    PKI_init_all();

    if (argc < 3)
    {
        PrintUsage();
        exit(1);
    }


    if (0 == strcmp(argv[1], "genrequest"))
    {
        long long serial = 0;
        sscanf(argv[2], "%lld", &serial);
        genrequest(serial);
    }
    else if (0 == strcmp(argv[1], "genresponse"))
    {
        PKI_OCSP_CERTSTATUS certStatus = -1;
        if (0 == strcmp(argv[2], "good"))
        {
            certStatus = PKI_OCSP_CERTSTATUS_GOOD;
        }
        else if (0 == strcmp(argv[2], "revoked"))
        {
            certStatus = PKI_OCSP_CERTSTATUS_REVOKED;
        }
        else if (0 == strcmp(argv[2], "unknown"))
        {
            certStatus = PKI_OCSP_CERTSTATUS_UNKNOWN;
        }
        else
        {
            printf("Unknown response type: %s.\n", argv[2]);
            PrintUsage();
            exit(1);
        }       
        genresponse(certStatus);
    }
    else
    {
        PrintUsage();
        exit(1);
    }
    return 0;
}