Questions on gss_verify_mic_iov
ghudson at mit.edu
Wed Sep 16 01:17:26 EDT 2015
On 09/16/2015 12:29 AM, Natalie Li wrote:
> EType: aes256-cts-hmac-sha1-96 (18) as shown in frame 25. See (1) of the
> attached doc.
> Size of the MIC token is 32 bytes as shown in frame 37. See (2) of the
> attache doc.
The AES enctypes use a checksum length of 12 bytes. There are an
additional 16 bytes of GSSAPI token header, for an expected total of 28
bytes. In checksum_iov_v3() we check for an exact match against this
expected length, so the 32-byte token yields an error.
Looking at the packet capture, the MIC token ends with twelve non-zero
checksum bytes followed by four zero bytes, which I assume are padding.
This padding appears to conform to [MS-RPCE] 126.96.36.199; I don't know if
there is any way to find out the true length of the token without the
padding. (Removing zero bytes is of course not safe; nothing prevents
the last byte of the checksum from being zero.)
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