Writing a NegoEx security package: development notes

Run mstsc (the Remote Desktop client) with a breakpoint in the security package.

Or write an SSPI test program that calls SspiExcludePackage to exclude NTLMSP_NAME, MICROSOFT_KERBEROS_NAME, and NEGOSSP_NAME.

SpAcquireCredentialsHandle

This code reads the user name and the password (or the certificate SHA1 and the PIN). PSEC_WINNT_AUTH_PACKED_CREDENTIALS is defined in sspi.h.

#define _SEC_WINNT_AUTH_TYPES
#include <sspi.h>

if (!MyLsaDispatchTable->GetCallInfo(&CallInfo)) {
    // handle error
}
if (CallInfo.Attributes & SECPKG_CALL_NEGO_EXTENDER && AuthorizationData != NULL) {
    PSECPKG_CREDENTIAL pGivenCredential = (PSECPKG_CREDENTIAL) AuthorizationData;
    PSECPKG_SUPPLIED_CREDENTIAL pSuppliedCredentials =
        (PSECPKG_SUPPLIED_CREDENTIAL)((PBYTE)AuthorizationData
            + pGivenCredential->MarshaledSuppliedCreds.ByteArrayOffset);
    PSEC_WINNT_AUTH_PACKED_CREDENTIALS pPackedCredentials =
        (PSEC_WINNT_AUTH_PACKED_CREDENTIALS)((PBYTE)pSuppliedCredentials
            + pSuppliedCredentials->PackedCredentials.ByteArrayOffset);
    MyLsaDispatchTable->LsaUnprotectMemory(
        pPackedCredentials,
        pSuppliedCredentials->PackedCredentials.ByteArrayLength);
    PSEC_WINNT_AUTH_DATA pAuthData = &(pPackedCredentials->AuthData);
    if (!IsEqualGUID(pAuthData->CredType, SEC_WINNT_AUTH_DATA_TYPE_PASSWORD)) {
        // handle wrong credential type
    }
    // Read username
    szCredential = EIDAlloc((pSuppliedCredentials->UserName.ShortArrayCount + 1) * sizeof(WCHAR));
    memcpy(szCredential,
           (PBYTE)pSuppliedCredentials + pSuppliedCredentials->UserName.ShortArrayOffset,
           pSuppliedCredentials->UserName.ShortArrayCount * sizeof(WCHAR));
    ((WCHAR*)szCredential)[pSuppliedCredentials->UserName.ShortArrayCount] = 0;
    // Read password
    PBYTE pbData = ((PBYTE)pPackedCredentials + pAuthData->CredData.ByteArrayOffset);
    dwPasswordWSizeInBytes = pAuthData->CredData.ByteArrayLength + sizeof(WCHAR);
    szPasswordW = (PWSTR)EIDAlloc(dwPasswordWSizeInBytes);
    memcpy(szPasswordW, pbData, pAuthData->CredData.ByteArrayLength);
    szPasswordW[(pAuthData->CredData.ByteArrayLength / 2)] = 0;
}

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SpQueryMetaData

LSA passes the context handle returned by SpQueryMetaData back to SpExchangeMetaDataFn and to SpInitLsaContext / SpAcceptLsaContext. It is NULL on the first call, then keeps the value set by the previous call. So after a metadata exchange, SpInitLsaContext can get a non-null context.

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NegoKey

Before the negotiation (SpInitLsaContext or SpAcceptLsaContext), LSA calls SpQueryContextAttributes(SECPKG_ATTR_NEGO_KEYS) with the handle returned by SpQueryMetaData and SpExchangeMetaData.

• The buffer is a PSecPkgContext_NegoKeys. Zero it on the first call.
• Allocate the memory from the LSA private heap.
• The key type is a constant from RFC 3961 (also in NTSECAPI.h).
• aes128-cts-hmac-sha1-96 (17) with a 128-bit key works.