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From "Linton Miller (JIRA)" <>
Subject [jira] [Created] (WSS-300) SubjectKeyIidentifier (SKI) incorrectly calculated for 2048-bit RSA key
Date Thu, 14 Jul 2011 20:17:00 GMT
SubjectKeyIidentifier (SKI) incorrectly calculated for 2048-bit RSA key

                 Key: WSS-300
             Project: WSS4J
          Issue Type: Bug
          Components: WSS4J Core
    Affects Versions: 1.6.1, 1.5.11
         Environment: Tomcat 5, Solaris 10, Java 1.4 and Tomcat 6, Win XP, Java 6
            Reporter: Linton Miller
            Assignee: Colm O hEigeartaigh

The crypto function to get the SubjectKeyIdentifier from an X509Certificate has incorrect
hard-coded assumptions about the size of the encoded information, meaning the calculation
of the SKI from a 2048-bit RSA key is incorrect.

The method does not
parse the DER encoding of information, but just tries to pick out the piece of the byte array
that corresponds to the content of interest. However, that approach fails because the DER
encoding is variable length, depending on the size of the data being encoded. e.g. a 1024-bit
key in a DER BIT STRING takes 4 bytes header +  140 bytes data to encode, whereas a 2048-bit
key takes 5 bytes header + 270 bytes data; the header is one byte longer for the larger key,
so the data starts at a different point in the array.

To fix this, the DER data structures should be properly processed, reading the DER header
bytes to determine the length of each data element (that also allows the generalization of
handling any X.509 encoded public key, rather than just RSA keys as currently coded).

Attached is a suggested patch (against WSS4J 1.6.1) that implements this idea: it processes
the SubjectPublicKeyInfo and SubjectKeyIdentifier DER-encoded byte arrays according to their
ASN.1 definitions from RFC 3280/5280 to pick out the desired data bytes.

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