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From "Linton Miller (JIRA)" <>
Subject [jira] [Updated] (WSS-300) SubjectKeyIidentifier (SKI) incorrectly calculated for 2048-bit RSA key
Date Thu, 14 Jul 2011 20:18:59 GMT


Linton Miller updated WSS-300:


> SubjectKeyIidentifier (SKI) incorrectly calculated for 2048-bit RSA key
> -----------------------------------------------------------------------
>                 Key: WSS-300
>                 URL:
>             Project: WSS4J
>          Issue Type: Bug
>          Components: WSS4J Core
>    Affects Versions: 1.5.11, 1.6.1
>         Environment: Tomcat 5, Solaris 10, Java 1.4 and Tomcat 6, Win XP, Java 6
>            Reporter: Linton Miller
>            Assignee: Colm O hEigeartaigh
>         Attachments:,,
> 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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