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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.

WHAT SCEP?

(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.

SSCEP FEATURES

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:

OpenBSD AIX Darwin (PowerPC, no universal binaries yet) Tandem NonStop (Guardian), OSS environment, MIPS processor Linux x86 z/OS (USS environment) Solaris Windows, compiled with VC6, statically linked with OpenSSL 0.9.7i

Unix:

To compile run: $ make

Windows:

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.

  1. 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.

  2. 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

$ make

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:

Key		Explanation
=====================================================================

CACertFile	  This is one is needed with all operations.
              Example: ./ca.crt
              Command line option: -c

CAIdentifier  Some CAs require you to define this. Example: mydomain.com
              Command line option: -i

CertReqFile   Certificate request file created with mkrequest.
              Example: ./local.csr
              Command line option: -r

Debug         Debug? Answer "yes" or "no". 
              Command line option: -d

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).
              Command line option: -E

EncCertFile   If your CA/RA uses a different certificate for encyption
              and signing, define this. CACertFile is used for verifying
              the signature. Example: ./enc.crt
              Command line option: -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
              signature private key file (-K, SignKeyFile). 
              Example: ./sig.crt
              Command line option: -O

SignKeyFile   See SignCertFile. Specifies the corresponding private key.
              Example: ./sig.key
              Command line option: -K

FingerPrint   Display fingerprint algorithm. Available algorithms are md5
              and sha1. Default is md5.
              Command line option: -F

GetCertFile   Write certificate asquired via getcert operation.
              Example: ./cert.crt
              Command line option: -w

GetCertSerial Certificate serial number. Define this for getcert. The value
              is defined as a decimal number. Example: 12
              Command line option: -s

GetCrlFile    Write CRL to file. Example: ./crl.crl
              Command line option: -w

LocalCertFile Write successfully enrolled certificate. Example: ./local.crt
              Command line option: -l

MaxPollCount  Max number of GetCertInitial requests. Example: 50
              Command line option: -n

MaxPollTime   Max polling time in seconds. Example: 28800
              Command line option: -T

PollInterval  Poll periodically for pending certificate. Example: 60
              Command line option: -t

PrivateKeyFile  Private key created with mkrequest. Example: ./local.key
                Command line option: -k

Proxy         Use HTTP proxy at host:port. Example: localhost:8080
              Command line option: -p

SelfSignedFile Write optionally the selfsigned certificate in file (needed
               in SCEP transaction). Example: ./selfsigned.crt
               Command line option: -L

SigAlgorithm  PKCS#7 signature algorithm. Available algorithms are md5
              and sha1. Default is md5.
              Command line option: -E

URL           URL of the SCEP server. Example:
              http://localhost/cgi-bin/pkiclient.exe
              Command line option: -u

Verbose       Verbose? Answer "yes" or "no"
              Command line option: -v

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 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.

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

CREDITS

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.

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