Copyright (c) Jarkko Turkulainen 2003. All rights reserved.
See the file COPYRIGHT for licensing information.
SSCEP is a client-only implementation of the SCEP (Cisco System's Simple Certificate Enrollment Protocol). SSCEP is designed for OpenBSD's isakmpd, but it will propably work with any Unix system with a recent compiler and OpenSSL toolkit libraries installed.
(From the Cisco Systems White Paper):
SCEP is a PKI communication protocol which leverages existing technology by using PKCS#7 and PKCS#10. SCEP is the evolution of the enrollment protocol developed by Verisign, Inc. for Cisco Systems, Inc. It now enjoys wide support in both client and CA implementations.
The goal of SCEP is to support the secure issuance of certificates to network devices in a scalable manner, using existing technology whenever possible. The protocol supports the following operations:
- CA and RA public key distribution
- Certificate enrollment
- Certificate and CRL query
Certificate and CRL access can be achieved by using the LDAP protocol, or by using the query messages defined in SCEP.
Currently, SSCEP implements:
- All of the SCEP operations using SCEP query messages
- HTTP/1.1 queries via IPv4 or IPv6
- Integration with OpenSSL cryptographic engines
There's no LDAP support, and probably there will never be (that's why it is simple).
SSCEP has been tested successfully against the following CA products:
- OpenXPKI (getcaps, getca, enroll and automatic approval works)
- OpenSCEP server (getca, enroll and getcrl works)*
- Windows2000 server CA + Microsoft SCEP module (works)
- SSH Certifier (getca and enroll works)
- iPlanet CMS (getca and enroll works)*
- VeriSign Onsite (getca and enroll works)**
- Entrust VPN Connect (getca and enroll works)***
- OpenCA (getca, enroll, getcrl and automatic approval works)
(*) by default, subjectAltName extensions are dropped from certificate
(**) only DNS subjectAltName allowed (demo mode)
(***) demo requires to use /C=US/O=Entrust
The program should compile on the following systems:
- Linux
- OpenBSD
- AIX
- Darwin (PowerPC, no universal binaries yet)
- Tandem NonStop (Guardian), OSS environment, MIPS processor
- z/OS (USS environment)
- Solaris
- Windows
In general, two build systems are supported:
- GNU Autotools (autoconf, automake, libtool)
- CMake
Prerequisites:
- OpenSSL crypto library
- sscep 0.3.0 - 0.6.1 works with openssl 0.9.7 - 1.0.2
- sscep 0.7.0 - 0.9.1 works with openssl 0.9.7 - 1.1.1
- sscep 0.10.0 works with openssl 1.1.0 - 3.0.0
To compile run:
$ make
To generate the configure script when checking out from github source:
$ ./bootstrap.shTo compile from a tarball created with 'make dist'
$ ./configure
$ make
$ make installTo build a RPM package from the tarball do
cp sscep-*.tar.gz ~/rpmbuild/SOURCES
rpmbuild -ba scripts/sscep.spec-
Download and install:
- Microsoft Visual Studio (e.g. the Community Edition) from https://visualstudio.microsoft.com/downloads
- CMake from https://cmake.org/download
- Win32/Win64 OpenSSL from http://slproweb.com/products/Win32OpenSSL.html
-
Start the CMake GUI, select Where is the source code and Where to put the binaries (it could be the same), then Configure and Generate the project files.
-
Start the Visual Studio, open the generated Solution (sscep.sln) and build the project. Then copy the sscep binary (Debug or Release) and configuration file sscep.conf somewhere.
Install a few packages from Homebrew:
$ brew install autoconf automake libtool pkg-config opensslTo generate the configure script when checking out from github source:
$ glibtoolize
$ aclocal
$ automake -a -c -f
$ autoreconfSet PKG_CONFIG_PATH and then the usual will work:
$ export PKG_CONFIG_PATH="/usr/local/opt/openssl@1.1/lib/pkgconfig"
$ ./configure
$ make
$ make installRunning the command "sscep" without any arguments should give you a list of arguments and command line options.
$ ./sscep
sscep version 0.9.x
Usage: ./sscep OPERATION [OPTIONS]
Available OPERATIONs are
getca Get CA/RA certificate(s)
enroll Enroll certificate
getcert Query certificate
getcrl Query CRL
getcaps Query SCEP capabilities
General OPTIONS
-u <url> SCEP server URL
-p <host:port> Use proxy server at host:port
-g <engine> Use the given cryptographic engine
-f <file> Use configuration file
-c <file> CA certificate file or '-n' suffixed files (write if OPERATION is getca)
-E <name> PKCS#7 encryption algorithm (des|3des|blowfish|aes[128]|aes192|aes256)
-S <name> PKCS#7 signature algorithm (md5|sha1|sha224|sha256|sha384|sha512)
-W <secs> Wait for connectivity, up to <secs> seconds
-v Verbose output (for debugging the configuration)
-d Debug output (more verbose, for debugging the implementation)
OPTIONS for OPERATION getca are
-i <string> CA identifier string
-F <name> Fingerprint algorithm (md5|sha1|sha224|sha256|sha384|sha512)
OPTIONS for OPERATION enroll are
-k <file> Private key file
-r <file> Certificate request file
-K <file> Signature private key file, use with -O
-O <file> Signature certificate (used instead of self-signed)
-l <file> Write enrolled certificate in file
-e <file> Use different CA cert for encryption
-L <file> Write selfsigned certificate in file
-t <secs> Polling interval in seconds
-T <secs> Max polling time in seconds
-n <count> Max number of GetCertInitial requests
-R Resume interrupted enrollment
OPTIONS for OPERATION getcert are
-k <file> Signature private key file
-l <file> Signature local certificate file
-s <number> Certificate serial number (decimal)
-w <file> Write certificate in file
OPTIONS for OPERATION getcrl are
-k <file> Signature private key file
-l <file> Signature local certificate file
-w <file> Write CRL in fileSSCEP also supports configuration via a configuration file (-f).
This is the recommended way to configure SSCEP and all the examples
in below assume that you have done so.
All configuration options are key-value pairs separated with the equal sign and grouped into sections:
[section]
Key = Value
Quotation marks are optional - they are needed only if the value contains space characters (space or tab). Quotation marks inside the value string must be escaped using a backslash:
Key = "Value \"containing quotation marks\""
Comment lines (lines starting with '#') and empty lines are discarded.
Here are the available configuration file keys and example values:
| Key | Explanation | Example | Command options |
|---|---|---|---|
| URL | URL of the SCEP server. | http://example.com/scep |
-u |
| CACertFile | Sigle CA certificate file, or mutiple CA certificates suffixed with -0, -1, ... to write (getca) or to choose from (all other operations). |
./ca.crt |
-c |
| CAIdentifier | Some CAs require you to define this. | mydomain.com |
-i |
| CertReqFile | Certificate request file created with mkrequest. | ./local.csr |
-r |
| EncAlgorithm | PKCS#7 encryption algorithm. Available algorithms are des, 3des, blowfish, aes/aes128, aes192 and aes256. NOTE: SCEP provides no mechanism to "negotiate" the algorithm - even if you send 3des, reply might be des (same thing applies to SigAlgorithm). | -E |
|
| EncCertFile | If your CA/RA uses a different certificate for encyption and signing, define this. CACertFile is used for verifying the signature. | ./enc.crt |
-e |
| SignCertFile | Instead of creating a self-signed certificate from the new key pair use an already existing certficate/key to sign the SCEP request. If the "old" certificate and key is used, the CA can verify that the holder of the private key for an existing certificate re-enrolls for a renewal certificate, allowing for automatic approval of the request. Requires specification of the corresponding SignKeyFile (-K). |
./sig.crt |
-O |
| SignKeyFile | See SignCertFile. Specifies the corresponding private key. | ./sig.key |
-K |
| FingerPrint | Display fingerprint algorithm. Available algorithms are md5, sha1, sha224, sha256, sha384 and sha512. Default is the best from getcacaps, or md5. | -F |
|
| GetCertFile | Write certificate asquired via getcert operation. | ./cert.crt |
-w |
| GetCertSerial | Certificate serial number. Define this for getcert. The value is defined as a decimal number. | 12 |
-s |
| GetCrlFile | Write CRL to file. | ./crl.crl |
-w |
| LocalCertFile | Write successfully enrolled certificate. | ./local.crt |
-l |
| MaxPollCount | Max number of GetCertInitial requests. | 50 |
-n |
| MaxPollTime | Max polling time in seconds. | 28800 |
-T |
| PollInterval | Poll periodically for pending certificate. | 60 |
-t |
| PrivateKeyFile | Private key created with mkrequest. | ./local.key |
-k |
| Proxy | Use HTTP proxy at host:port. | localhost:8080 |
-p |
| SelfSignedFile | Write optionally the selfsigned certificate in file (needed in SCEP transaction). | ./selfsigned.crt |
-L |
| SigAlgorithm | PKCS#7 signature algorithm. Available algorithms are md5, sha1, sha224, sha256, sha384 and sha512. Default is the best from getcacaps, or md5. | -S |
|
| Verbose | Verbose output? Answer "yes" or "no" | -v |
|
| Debug | Debug output? Answer "yes" or "no". | -d |
The actual enrollment is done with the following procedure:
- CA server identification string If your SCEP server requires you to use a specific identification string in the initial CA certificate access (step 3), write it down.
- CA server http URL
You must know the complete url, with http:// and cgi-program path and
everything. Example:
http://pkiserver.company.com/cgi-bin/pkiclient.exe - CA naming policy You need to know what kind of DN you request. Some may require you to use unstructuredName naming, some may require a CN with localityName, etc.
Before the enrollment can take place, sscep needs a private key file and the corresponding X.509 certificate request in PKCS#10 format.
This can be created using the mkrequest script, or manually by openssl. Create an request.cnf, such as:
oid_section = new_oids
[ req ]
default_bits = 2048
default_keyfile = local.key
encrypt_key = no
distinguished_name = req_dn
attributes = req_attributes
req_extensions = req_ext
[ new_oids ]
certTemplateName = 1.3.6.1.4.1.311.20.2
[ req_dn ]
0.domainComponent = org
1.domainComponent = OpenXPKI
2.domainComponent = Test Deployment
commonName = device
[ req_attributes ]
[ req_ext ]
basicConstraints = critical, CA:FALSE
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth, clientAuth
subjectAltName = @alt_names
certTemplateName = ASN1:UTF8String:pc-client
[ alt_names ]
DNS.1 = www.example.com
DNS.2 = example.com
To create a key and a request named local.key and local.csr run:
$ openssl req -new -config request.cnf -out local.csrYou can automate this process using the mkrequest shell script. Edit the DN variables in the mkrequest file if you need. When ready, make the request:
$ mkrequest -ip 172.30.0.1
Generating RSA private key, 1024 bit long modulus
..............++++++
...++++++
e is 65537 (0x10001)
Using configuration from .4018client.cnfThis also writes key and request named local.key and local.csr (you can change the "local" with variable PREFIX in mkrequest).
If the CA supports automatic enrollment, you may supply the password in cert request:
$ mkrequest -ip 172.30.0.1 password$ ./sscep getca -u http://example.com/scep -c ca.crt
./sscep: requesting CA certificate
./sscep: valid response from server
./sscep: MD5 fingerprint: 1D:3C:4C:DF:99:73:B8:FB:B4:EE:C4:56:A9:7C:37:A3
./sscep: CA certificate written as ca.crtNOTE: it is very important to make sure that the CA certificate is really what you think it is. The security of the whole protocol depends on that!! This is why the fingerprint is printed on terminal - you should check that from your CA. You can check the fingerprint any time with command
$ openssl x509 -in ca.crt -noout -fingerprintIf the CA sends a certificate chain, sscep writes all certificates in the order it founds them in reply and names them with an integer suffix (-number) appended to CACertFile.
$ ./sscep getca -u http://example.com/scep -c ca.crt
./sscep: requesting CA certificate
./sscep: valid response from server
./sscep: found certificate with
subject: /C=FI/O=klake.org/CN=klake.org VPN RA
issuer: /C=FI/O=klake.org/CN=klake.org VPN CA
usage: Digital Signature, Non Repudiation
MD5 fingerprint: 7A:92:84:2A:6F:EE:28:14:F9:69:D8:9D:61:34:B5:67
./sscep: certificate written as ca.crt-0
./sscep: found certificate with
subject: /C=FI/O=klake.org/CN=klake.org VPN CA
issuer: /C=FI/O=klake.org/CN=klake.org VPN CA
usage: Digital Signature, Non Repudiation, Certificate Sign, CRL Sign
MD5 fingerprint: A5:CE:94:5C:96:77:94:E8:F5:31:AB:D5:31:18:1D:E1
./sscep: certificate written as ca.crt-1SSCEP prints out issuer, subject, key usage and md5/sha1 fingerprint for
each certificate it founds. This information might help you to decide what
certificate to use as -c and (optionally) -e in subsequent operations.
Some CAs may give you a three (or more) certificates, the root CA(s) plus
different RA certificates for encryption and signing. If that's your case,
you have to define encryption certificate with command line option (-e).
Probably it is the certificate with key usage "Key Encipherment".
You may also use the base name (e.g. ca.crt) of all certificates and
rely on an automated certificate selection. The system loads all available
certificates (ca.crt-0, ca.crt-1, ...) and then:
- Tries to find a certificate that:
- Is at the end of the received chain, i.e. do not sign other certificate.
- Has key usage "Digital Signature" (for
-c) or "Key Encipherment" (for-e), or does not have any key usage defined.
- If no such key is found, selects the first certificate in the chain, which is usually the right certificate anyway.
Currently, SSCEP doesn't verify the CA/RA certificate chain. You can do it manually with OpenSSL:
$ openssl verify -CAfile ca.crt-1 ca.crt-0
ca.crt-0: OKNOTE: In case of multiple CA/RA certificates, the actual CA (the one who signs your certificate) might not be the same as the CA/RA you are dealing with. Keep this in mind when installing the CA cert in /etc/isakmpd/ca.
You need to supply URL (-u), CACertFile (-c), PrivateKeyFile (-k),
CertReqFile (-r) and output LocalCertFile (-l). PrivateKeyFile is the key
generated in step 2 (local.key), CertReqFile is the request (local.csr)
and LocalCertFile is where the enrolled certificate will be written once ready.
If your CA/RA have different certificates for encryption and signing, and you
do not want to use the auto-selection mechanism, you must provide also the
encryption certificate EncCertFile (-e).
Normally, the enrollment looks like this:
$ ./sscep enroll -u http://example.com/scep -c ca.crt -k local.key -r local.csr -l local.crt
./sscep: sending certificate request
./sscep: valid response from server
./sscep: pkistatus: PENDING
./sscep: requesting certificate (#1)
./sscep: valid response from server
./sscep: pkistatus: PENDING
./sscep: requesting certificate (#2)
./sscep: valid response from server
./sscep: pkistatus: PENDING
....
./sscep: requesting certificate (#NNN)
./sscep: valid response from server
./sscep: pkistatus: SUCCESS
./sscep: certificate written as ./local.crtFirst message sent is PKCSReq, that's where your request goes. Then the CA
writes request down and sends reply PENDING, indicating that the certificate
is not signed yet. SSCEP polls periodically for the certificate by sending
GetCertInitial messages until the CA returns SUCCESS. The polling interval
can be adjusted with PollInterval (-t). You can interrupt the process any
time and start again using "sscep enroll ..". You should use the command line
option (-R) when you continue (resume) the interrupted enrollment.
If the CA is configured for automatic enrollment (and your request includes the challenge password), it returns SUCCESS as a first reply. Otherwise, the enrollment requires manual signing and authentication (perhaps a phone call).
The SCEP allows to use the existing certificate (issued by the CA) to authenticate a renewal request. In this context, the SCEP request with the new public key is signed with the old certificate and key (instead of using a self-signed certificate created from the new key pair).
If you want to renew the certificate created previously (local.crt), you
follow the enrollment procedure as described before, but supply the current
(old) key and certificate as SignKeyFile (-K) and SignCertFile (-O).
$ ./sscep enroll -u http://example.com/scep -c ca.crt -K local.key -O local.crt \
-k new.key -r new.csr -l new.crtThe actual behaviour of the SCEP server depends on the CA policy and on the capabilities of the SCEP server (not all servers implement this feature, using the existing certificate with an older SCEP server may or may not work, depending on implementation).
Note: For example, OpenXPKI is capable of automatically approving SCEP requests signed with the already existing key pair.
Install local.key, local.crt and ca.crt in the isakmpd default locations and you are ready to go! Default locations are
Private key /etc/isakmpd/private/local.key Certificate /etc/isakmpd/certs/local.crt CA certificate /etc/isakmpd/ca/ca.crt
And pay attention to CA certificate if your enrollment was done via RA
server. openssl verify -CAfile ca.crt local.crt is your friend here.
You need your enrolled certificate for this step.
$ ./sscep getcrl -f sscep.conf
./sscep: requesting crl
./sscep: valid response from server
./sscep: pkistatus: SUCCESS
./sscep: CRL written as ./crl.crlI'd like to thank the following people for providing me feedback:
Fiel Cabral, Manuel Gil Perez
OpenSSL toolkit made this possible.
I would also like to thank OpenSCEP project for it's great software, reading the source code helped me understand the protocol. Unfortunately, it's license is too restrictive for my use.