SSCEP - Simple SCEP client for Unix
Copyright (c) Jarkko Turkulainen 2003. All rights reserved.
See the file COPYRIGHT for licensing information.
WHAT IS SSCEP?
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. 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:
- 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
(****) automatic approval according to newer SCEP drafts requires OpenCA 0.9.2.4 or higher
HOW TO COMPILE
The program should compile on the following systems:
- Darwin (PowerPC, no universal binaries yet)
- Tandem NonStop (Guardian), OSS environment, MIPS processor
- Linux x86
- z/OS (USS environment)
- Windows, compiled with VC6, statically linked with OpenSSL 0.9.7i
To compile run:
To generate the configure script when checking out from github source:
$ automake -a -c -f
To compile from a tarball created with 'make dist'
$ make install
The Win32 version of sscep has been tested with OpenSSL-v0.9.7i. For Win32 environment you can choose two ways to compile the sscep program.
Dynamically linked against the binary OpenSSL distribution: http://www.slproweb.com/download/Win32OpenSSL-v0.9.7i.exe For this you need the binaries from OpenSSL-v0.9.7i and change the paths in the makefile Makefile.w32. This works with VC6.0 but not with VC7.0.
Statically linked against OpenSSL-v0.9.7i. You can download the source from the OpenSSL Homepage and you have to change the paths in the makefile Makefile.w32. This OpenSSL Version needs to be compiled with the same compiler as sscep, because otherwise you can get some trouble with diffrent LIBs.
If you want to use a debug version of sscep, then you need to compile a debug version of OpenSSL.
To compile run:
C:\...> vcvars32.bat C:\...> nmake -f Makefile.w32
Copy binary file sscep and configuration file sscep.conf to somewhere.
The program should compile on OpenBSD system without problems. Uncompress the package and run command
Copy binary file sscep and configuration file sscep.conf to somewhere.
HOW TO USE
Running the command "sscep" without any arguments should give you a list of arguments and command line options.
$ ./sscep sscep version 2005XXXX Usage: ./sscep OPERATION [OPTIONS] Available OPERATIONs are getca Get CA/RA certificate(s) enroll Enroll certificate getcert Query certificate getcrl Query CRL General OPTIONS -u <url> SCEP server URL -p <host:port> Use proxy server at host:port -f <file> Use configuration file -c <file> CA certificate file (write if OPERATION is getca) -E <name> PKCS#7 encryption algorithm (des|3des|blowfish) -S <name> PKCS#7 signature algorithm (md5|sha1) -v Verbose operation -d Debug (even more verbose operation) OPTIONS for OPERATION getca are -i <string> CA identifier string -F <name> Fingerprint algorithm (md5|sha1) OPTIONS for OPERATION enroll are -k <file> Private key file -r <file> Certificate request file -K <file> Signature private key file -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> Private key file -l <file> Local certificate file -s <number> Certificate serial number (decimal) -w <file> Write certificate in file OPTIONS for OPERATION getcrl are -k <file> Private key file -l <file> Local certificate file -w <file> Write CRL in file
SSCEP 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 one or more space characters:
"Key" [spaces] "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" [spaces] "Value "containing quotation marks""
Comment lines (lines starting with '#') and empty lines are discarded.
Here are the available configuration file keys and example values:
|CACertFile||This is one is needed with all operations.||
|CAIdentifier||Some CAs require you to define this.||
|CertReqFile||Certificate request file created with mkrequest.||
|Debug||Debug? Answer "yes" or "no".||
|EncAlgorithm||PKCS#7 encryption algorithm. Available algorithms are des, 3des and blowfish. NOTE: this could be very misleading, current SCEP draft provides no mechanism to "negotiate" the algorithm - even if you send 3des, reply might be des (same thing applies to SigAlgorithm).||
|EncCertFile||If your CA/RA uses a different certificate for encyption and signing, define this. CACertFile is used for verifying the signature.||
|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 signature private key file (-K, SignKeyFile).||
|SignKeyFile||See SignCertFile. Specifies the corresponding private key.||
|FingerPrint||Display fingerprint algorithm. Available algorithms are md5 and sha1. Default is md5.||
|GetCertFile||Write certificate asquired via getcert operation.||
|GetCertSerial||Certificate serial number. Define this for getcert. The value is defined as a decimal number.||
|GetCrlFile||Write CRL to file.||
|LocalCertFile||Write successfully enrolled certificate.||
|MaxPollCount||Max number of GetCertInitial requests.||
|MaxPollTime||Max polling time in seconds.||
|PollInterval||Poll periodically for pending certificate.||
|PrivateKeyFile||Private key created with mkrequest.||
|Proxy||Use HTTP proxy at host:port.||
|SelfSignedFile||Write optionally the selfsigned certificate in file (needed in SCEP transaction).||
|SigAlgorithm||PKCS#7 signature algorithm. Available algorithms are md5 and sha1. Default is md5.||
|URL||URL of the SCEP server.||
|Verbose||Verbose? Answer "yes" or "no"||
The actual enrollment is done with the following procedure:
STEP 1 - Gather information
- 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
- 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.
STEP 2 - Make certificate request and key
Before the enrollment can take place, sscep needs a private key file and the corresponding X.509 certificate request in PKCS#10 format. Edit the DN variables in the file mkrequest (it's a shell script) 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.cnf
This 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
STEP 3 - Get CA certificate
Configure the URL and CACertFile in configuration file (sscep.conf) and run the command
$ ./sscep getca -f sscep.conf ./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.crt
NOTE: 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 -fingerprint
If the CA sends a certificate chain, sscep writes all certificates in the order it founds them in reply and names them with an integer prefix (-number) appended to CACertFile.
$ ./sscep getca -f sscep.conf ./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-1
SSCEP 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. 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) or with conf file keyword EncCertFile. Probably it is the certificate with key usage "Key Encipherment".
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: OK
NOTE: 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.
STEP 4 - Make enrollment
You need to supply configuration file keys URL, CACertFile, PrivateKeyFile, LocalCertFile and CertReqFile. 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, you must also provide the encryption certificate (EncCertFile).
Normally, the enrollment looks like this:
$ ./sscep enroll -f sscep.conf ./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.crt
First 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, or command line option (-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 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).
Newer SCEP draft versions allow 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). To use this feature, use the command line options -O and -K to specify the old certificate and private key (SignCertFile and SignCertKey in the configuration file). The 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: Newer versions of OpenCA (http://www.openca.info/) support an SCEP server that is capable of automatically approving SCEP requests signed with the already existing key pair.
STEP 5 - Use certificate
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.
STEP 6 - Check out revocation list (optional)
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.crl
I'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.