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CRL verification failure while using multiple issuer certs with same subject

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x...@bremen.de

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Feb 11, 2009, 12:15:31 PM2/11/09

Hi,

we're using a microsoft pki consisting of two stages - a root ca and
two sub cas.
The sub ca branch issuing user certificates has now more than one
valid ca cert, each managing its own crl. The problem occurs while
trying to check the validity of a given crl: openssl seems to be
unable to select the right ca cert for checking the crl signature and
following error occurs:

openssl crl -CApath /tmp/ssl -in /tmp/ssl/mySubCA-01.crl -noout
verify failure
openssl crl -CApath /tmp/ssl -in /tmp/ssl/mySubCA-02.crl -noout
verify OK

Both issuing ca certs have their hashed links in CApath. Since subject
name is the same, both links have the same name, but a different
number:
6187f748.0
6187f748.1

When i manually swap the hash links in the CApath, the result of the
crl signature check also swaps. This seems to me as if openssl can't
distinguish between the two ca certs, which use different keys and so
have different key id values. As a result, openssl seems only to try
the first hash-matching ca certificate and if it is the wrong one, the
signature check must fail.
My testing environment uses now openssl-0.9.8j built from source -
with the same results as in production (openssl 0.9.8g).

Is this a general interop problem between windows pki and openssl or
maybe we trigger an obscure bug on one side or the other?

Sebastian

x...@bremen.de

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Feb 16, 2009, 9:24:45 AM2/16/09

Sorry for answering myself.
The problem still persists and since no workaround could be found,
it's becoming more and more urgent.
To reproduce it, here's a simple test case including certificates and
crls:

> mkdir /tmp/testcase
> cd /tmp/testcase
# now, dump the attached certs and crls into their appropriate files
> ls
cacertificate1.pem cacertificate2.pem crl1.pem crl2.pem
# generate the hashes for the trusted ca certificates
> c_rehash ./
> openssl crl -CApath ./ -in crl1.pem -noout
verify failure
> openssl crl -CApath ./ -in crl2.pem -noout
verify OK

So, what's going wrong here? Openssl seems to check only the first ca
certificate
with matching subject hash and use it as the issuer of the crl to be
verified,
even if this is not actually true. Same behaviour with -CAfile option
instead of -CApath.

Sebastian

cacertificate1.pem
Subject_DN: /DC=de/O=PKI-Land-Bremen-Verwaltung/OU=Freie Hansestadt
Bremen/CN=Freie Hansestadt Bremen SubCA-01
Subject_hash: 6187f748
Subject kex identifier: 1C:FF:B1:47:BD:3E:C8:5F:8A:59:6E:2B:E3:3C:
56:EC:17:30:12:36

cacertificate2.pem
Subject_DN: /DC=de/O=PKI-Land-Bremen-Verwaltung/OU=Freie Hansestadt
Bremen/CN=Freie Hansestadt Bremen SubCA-01
Subject_hash: 6187f748
Subject kex identifier: 1A:51:68:3F:E1:67:59:0E:4A:08:CF:
1B:C6:B8:C4:54:94:6B:78:31

crl1.pem
Authority key identifier:1C:FF:B1:47:BD:3E:C8:5F:8A:59:6E:2B:E3:3C:
56:EC:17:30:12:36

crl2.pem
Authority key identifier:1A:51:68:3F:E1:67:59:0E:4A:08:CF:
1B:C6:B8:C4:54:94:6B:78:31

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