Problems with ldap userCertificate attribute

Question

I'm trying to use the 'userCertificate' attribute to hold a 'der' file. I can happily add my certificate using the ldif:

dn: cn=bob,ou=users,dc=home
changetype: modify
add: userCertificate;binary
userCertificate;binary:< file:///home/bob/cert.der

I see my certificate in base64 encoding when I do an ldapsearch and life seems good. But when I try to use ldapcompare:

ldapcompare -D"cn=admin,dc=home" -W "cn=bob,ou=users,dc=home" "userCertificate;binary:< file:///home/bob/cert.der"

I get the error:

Compare Result: Invalid syntax (21)
Additional info: unable to normalize value for matching
UNDEFINED

I get the same error if I try to compare using the base64 encoding

ldapcompare -D"cn=admin,dc=home" -W "cn=bob,ou=users,dc=home" "userCertificate:: base64encodedStringOfStuff"

Any ideas?

Answer 1

I just get this error: ldap_modify: Undefined attribute type (17) additional info: usercertificate: requires ;binary transfer.

This error message pretty clearly refers to what's mandated in RFC 4523, section 2.1. You simply always have to append ;binary to the attribute name in all LDAP operations affecting attribute userCertificate.

ldap_msgfree ldap_err2string Compare Result: Invalid syntax (21) Additional info: unable to normalize value for matching UNDEFINED

When using compare operation you have to look at which EQUALITY matching rule is available for the assertion attribute.

In subschema userCertificate is declared with EQUALITY certificateExactMatch based on issuer name and serial (see RFC 4523 section 2.5) which means there's no pure octet string match available for that attribute.

So you need to extract the decimal serial number and the issuer DN (LDAP string representation) from the certificate:

$ openssl x509 -noout -nameopt rfc2253 -serial -issuer -inform der -in ~/certs/[email protected] 
serial=0F560E
issuer=CN=StartCom Class 1 Primary Intermediate Client CA,OU=Secure Digital Certificate Signing,O=StartCom Ltd.,C=IL

Convert hex serial to decimal which is 1005070 in this example and invoke ldapcompare like this:

ldapcompare "cn=Michael Strö[email protected],dc=stroeder,dc=de" 'userCertificate;binary:{ serialNumber 1005070, issuer "cn=StartCom Class 1 Primary Intermediate Client CA,ou=Secure Digital Certificate Signing,o=StartCom Ltd.,c=IL"}'
TRUE

Additional notes:

• Be aware that DNs are complex beasts with escaping of special characters which need special treatment on shell command-line. Therefore I'd use a scripting language for this task to avoid some of the trouble.
• In opposite to modify operations and attribute retrieving you don't need the ;binary transfer type for compare operation. But with OpenLDAP it won't hurt either. Not sure about other LDAP server implementations.

Answer 2

Please note that I had a PEM encoded certificate, not a DER encoded one. You can use openssl to convert/display DER in PEM:

openssl x509 -in /home/bob/cert.der -inform DER

This command will display your certificate in PEM format. Something like this:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

I removed the top and the bottom lines just to have the Base64-encoded part. And, I executed the following command to load it into the usercertificate attribute:

$ ldapmodify -x -h my.ldap.server -Dcn=ADMIN_DN -W
Enter LDAP Password:

dn: uid=testuser,ou=users,o=foo.com    
changetype: modify
replace: usercertificate
usercertificate:: MIIDxTCCAq2gAwIBAgIQAqxcJmoLQJuPC3nyrkYldzANBgkqhkiG9w0BAQUFADBsMQswCQYDVQQG
 EwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3d3cuZGlnaWNlcnQuY29tMSsw
 KQYDVQQDEyJEaWdpQ2VydCBIaWdoIEFzc3VyYW5jZSBFViBSb290IENBMB4XDTA2MTExMDAwMDAw
 MFoXDTMxMTExMDAwMDAwMFowbDELMAkGA1UEBhMCVVMxFTATBgNVBAoTDERpZ2lDZXJ0IEluYzEZ
 MBcGA1UECxMQd3d3LmRpZ2ljZXJ0LmNvbTErMCkGA1UEAxMiRGlnaUNlcnQgSGlnaCBBc3N1cmFu
 Y2UgRVYgUm9vdCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMbM5XPm+9S75S0t
 Mqbf5YE/yc0lSbZxKsPVlDRnogocsF9ppkCxxLeyj9CYpKlBWTrT3JTWPNt0OKRKzE0lgvdKpVMS
 OO7zSW1xkX5jtqumX8OkhPhPYlG++MXs2ziS4wblCJEMxChBVfvLWokVfnHoNb9Ncgk9vjo4UFt3
 MRuNs8ckRZqnrG0AFFoEt7oT61EKmEFBIk5lYYeBQVCmeVyJ3hlKV9Uu5l0cUyx+mM0aBhakaHPQ
 NAQTXKFx01p8VdteZOE3hzBWBOURtCmAEvF5OYiiAhF8J2a3iLd48soKqDirCmTCv2ZdlYTBoSUe
 h10aUAsgEsxBu24LUTi4S8sCAwEAAaNjMGEwDgYDVR0PAQH/BAQDAgGGMA8GA1UdEwEB/wQFMAMB
 Af8wHQYDVR0OBBYEFLE+w2kD+L9HAdSYJhoIAu9jZCvDMB8GA1UdIwQYMBaAFLE+w2kD+L9HAdSY
 JhoIAu9jZCvDMA0GCSqGSIb3DQEBBQUAA4IBAQAcGgaX3NecnzyIZgYIVyHbIUf4KmeqvxgydkAQ
 V8GK83rZEWWONfqe/EW1ntlMMUu4kehDLI6zeM7b41N5cdblIZQB2lWHmiRk9opmzN6cN82oNLFp
 myPInngiK3BD41VHMWEZ71jFhS9OMPagMRYjyOfiZRYzy78aG6A9+MpeizGLYAiJLQwGXFK3xPkK
 mNEVX58Svnw2Yzi9RKR/5CYrCsSXaQ3pjOLAEFe4yHYSkVXySGnYvCoCWw9E1CAx2/S6cCZdkGCe
 vEsXCS+0yx5DaMkHJ8HSXPfqIbloEpw8nL+e/IBcm2PN7EeqJSdnoDfzAIJ9VNep+OkuE6N36B9K

modifying entry "uid=testuser,ou=users,o=foo.com"

$

Note the leading single space in front of each Base64-encoded line. It's the continuation marker in LDIF. And, when I search using ldapsearch, I see:

$ ldapsearch -LLL -x -h my.ldap.server -Dcn=ADMIN_DN -W -b ou=users,o=foo.com uid=testuser usercertificate
Enter LDAP Password:

dn: uid=testuser,ou=users,o=foo.com  
userCertificate;binary:: MIIDxTCCAq2gAwIBAgIQAqxcJmoLQJuPC3nyrkYldzANBgkqhkiG9
 w0BAQUFADBsMQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3d3
 cuZGlnaWNlcnQuY29tMSswKQYDVQQDEyJEaWdpQ2VydCBIaWdoIEFzc3VyYW5jZSBFViBSb290IEN
 BMB4XDTA2MTExMDAwMDAwMFoXDTMxMTExMDAwMDAwMFowbDELMAkGA1UEBhMCVVMxFTATBgNVBAoT
 DERpZ2lDZXJ0IEluYzEZMBcGA1UECxMQd3d3LmRpZ2ljZXJ0LmNvbTErMCkGA1UEAxMiRGlnaUNlc
 nQgSGlnaCBBc3N1cmFuY2UgRVYgUm9vdCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCgg
 EBAMbM5XPm+9S75S0tMqbf5YE/yc0lSbZxKsPVlDRnogocsF9ppkCxxLeyj9CYpKlBWTrT3JTWPNt
 0OKRKzE0lgvdKpVMSOO7zSW1xkX5jtqumX8OkhPhPYlG++MXs2ziS4wblCJEMxChBVfvLWokVfnHo
 Nb9Ncgk9vjo4UFt3MRuNs8ckRZqnrG0AFFoEt7oT61EKmEFBIk5lYYeBQVCmeVyJ3hlKV9Uu5l0cU
 yx+mM0aBhakaHPQNAQTXKFx01p8VdteZOE3hzBWBOURtCmAEvF5OYiiAhF8J2a3iLd48soKqDirCm
 TCv2ZdlYTBoSUeh10aUAsgEsxBu24LUTi4S8sCAwEAAaNjMGEwDgYDVR0PAQH/BAQDAgGGMA8GA1U
 dEwEB/wQFMAMBAf8wHQYDVR0OBBYEFLE+w2kD+L9HAdSYJhoIAu9jZCvDMB8GA1UdIwQYMBaAFLE+
 w2kD+L9HAdSYJhoIAu9jZCvDMA0GCSqGSIb3DQEBBQUAA4IBAQAcGgaX3NecnzyIZgYIVyHbIUf4K
 meqvxgydkAQV8GK83rZEWWONfqe/EW1ntlMMUu4kehDLI6zeM7b41N5cdblIZQB2lWHmiRk9opmzN
 6cN82oNLFpmyPInngiK3BD41VHMWEZ71jFhS9OMPagMRYjyOfiZRYzy78aG6A9+MpeizGLYAiJLQw
 GXFK3xPkKmNEVX58Svnw2Yzi9RKR/5CYrCsSXaQ3pjOLAEFe4yHYSkVXySGnYvCoCWw9E1CAx2/S6
 cCZdkGCevEsXCS+0yx5DaMkHJ8HSXPfqIbloEpw8nL+e/IBcm2PN7EeqJSdnoDfzAIJ9VNep+OkuE
 6N36B9K

$

I never got it working with the < file: directive against a DER or PEM file (without the CERTIFICATE markers). I'll do more investigation to see what's missing. However, if you reduce the multi-line the Base64-encoded certificate (PEM format) into a single line, then you can do the compare as

$ ldapcompare -x -Dcn=ADMIN_DN -W -h my.ldap.server uid=testuser,ou=users,o=foo.com 'usercertificate::MIIDxTCCAq2gAwIBAgIQAqxcJmoLQJuPC3nyrkYldzANBgkqhkiG9w0BAQUFADBsMQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3d3cuZGlnaWNlcnQuY29tMSswKQYDVQQDEyJEaWdpQ2VydCBIaWdoIEFzc3VyYW5jZSBFViBSb290IENBMB4XDTA2MTExMDAwMDAwMFoXDTMxMTExMDAwMDAwMFowbDELMAkGA1UEBhMCVVMxFTATBgNVBAoTDERpZ2lDZXJ0IEluYzEZMBcGA1UECxMQd3d3LmRpZ2ljZXJ0LmNvbTErMCkGA1UEAxMiRGlnaUNlcnQgSGlnaCBBc3N1cmFuY2UgRVYgUm9vdCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMbM5XPm+9S75S0tMqbf5YE/yc0lSbZxKsPVlDRnogocsF9ppkCxxLeyj9CYpKlBWTrT3JTWPNt0OKRKzE0lgvdKpVMSOO7zSW1xkX5jtqumX8OkhPhPYlG++MXs2ziS4wblCJEMxChBVfvLWokVfnHoNb9Ncgk9vjo4UFt3MRuNs8ckRZqnrG0AFFoEt7oT61EKmEFBIk5lYYeBQVCmeVyJ3hlKV9Uu5l0cUyx+mM0aBhakaHPQNAQTXKFx01p8VdteZOE3hzBWBOURtCmAEvF5OYiiAhF8J2a3iLd48soKqDirCmTCv2ZdlYTBoSUeh10aUAsgEsxBu24LUTi4S8sCAwEAAaNjMGEwDgYDVR0PAQH/BAQDAgGGMA8GA1UdEwEB/wQFMAMBAf8wHQYDVR0OBBYEFLE+w2kD+L9HAdSYJhoIAu9jZCvDMB8GA1UdIwQYMBaAFLE+w2kD+L9HAdSYJhoIAu9jZCvDMA0GCSqGSIb3DQEBBQUAA4IBAQAcGgaX3NecnzyIZgYIVyHbIUf4KmeqvxgydkAQV8GK83rZEWWONfqe/EW1ntlMMUu4kehDLI6zeM7b41N5cdblIZQB2lWHmiRk9opmzN6cN82oNLFpmyPInngiK3BD41VHMWEZ71jFhS9OMPagMRYjyOfiZRYzy78aG6A9+MpeizGLYAiJLQwGXFK3xPkKmNEVX58Svnw2Yzi9RKR/5CYrCsSXaQ3pjOLAEFe4yHYSkVXySGnYvCoCWw9E1CAx2/S6cCZdkGCevEsXCS+0yx5DaMkHJ8HSXPfqIbloEpw8nL+e/IBcm2PN7EeqJSdnoDfzAIJ9VNep+OkuE6N36B9K'
Enter LDAP Password:

TRUE
$

I'll update this if/when I can get it working with the < file: directive.