Hello list,
I'm running into some trouble with the SEC_PKCS7DecodeItem function. The input
for this function is a PKCS#7 EnvelopedData object, which contains just one
recipient, a session key (encrypted with the recipients' public key) and the
encrypted contents, encrypted with the above mentioned session key.
A slight oddity is that the encryption algorithm used does not get recognized
by NSS (it gives me "SEC_ERROR_NO_MODULE, because when it tries to find the
corresponding mechanism this yields 0xFFFF, for which there are of course no
appropriate modules).
The mechanism (ANSI-X9.42 DES3_CBC) is encoded as "1.2.840.10046.1.2", so I
had to add it by using SECOID_AddEntry like so:
std::string strDES3CBCOid("\x2a\x86\x48\xce\x3e\x01\x02", 7);
SECItem oDES3CBCOid;
oDES3CBCOid.type = siBuffer;
oDES3CBCOid.data = strDES3CBCOid.data();
oDES3CBCOid.len = strDES3CBCOid.length();
SECOidData oDES3CBC;
oDES3CBC.oid = oDES3CBCOid;
oDES3CBC.desc = "ANSI-X9.42-DES-EDE3-CBC";
oDES3CBC.mechanism = CKM_DES3_CBC;
oDES3CBC.supportedExtension = INVALID_CERT_EXTENSION;
SECOID_AddEntry(&oDES3CBC);
Now NSS does recognize the encryption algorithm used, but i get some
unexplained results. First of all, the plain data which would be present in the
returned ContentInfo structure is not 'plain' data at all, it seems to be
encrypted still. It is other data than I entered into the function, so that
leads me to believe that maybe the session key was not decrypted properly, or
maybe the above added mechanism is wrong. Any help here?
Also, if I do not provide a callback function for SEC_PKCS7DecodeItem, I get
only the last 7 bytes of the 'decrypted' data in the data field of the returned
SECItem structure, while the len filed indicates that there should have been
15637 bytes. If I do provide a callback however, I can see that it gets called
twice: the first time with 15630 bytes of data, the second time with the last 7
bytes. Is this (maybe) a bug?
Another 'oddity' I should mention, is that the PKCS#11 DLL which provides
access to the appropriate certificates and keys will ask for the proper
authentication itself - in other words, when a private-key function like
'decrypt', 'sign' or 'unwrap' is called, it checks if authentication is needed,
and asks for a password (via a message box). So I never need to provide any
password-callbacks, do I?
I hope I've explained matters properly, please blame my English skills if I
haven't ... I do. ;-)
Michiel van Meersbergen
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