/********************************************************************************/
/*										*/
/*			Context Management Command Support   			*/
/*			     Written by Ken Goldman				*/
/*		       IBM Thomas J. Watson Research Center			*/
/*            $Id: Context_spt.c 1603 2020-04-03 17:48:43Z kgoldman $		*/
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/********************************************************************************/

/* 7.3.1 Includes */
#include "Tpm.h"
#include "Context_spt_fp.h"
/* 7.3.2 Functions */
/* 7.3.2.1 ComputeContextProtectionKey() */
/* This function retrieves the symmetric protection key for context encryption It is used by
   TPM2_ContextSave() and TPM2_ContextLoad() to create the symmetric encryption key and iv */
void
ComputeContextProtectionKey(
			    TPMS_CONTEXT    *contextBlob,   // IN: context blob
			    TPM2B_SYM_KEY   *symKey,        // OUT: the symmetric key
			    TPM2B_IV        *iv             // OUT: the IV.
			    )
{
    UINT16           symKeyBits;    // number of bits in the parent's
    //   symmetric key
    TPM2B_PROOF      *proof = NULL;  // the proof value to use. Is null for
    //   everything but a primary object in
    //   the Endorsement Hierarchy
    BYTE             kdfResult[sizeof(TPMU_HA) * 2];// Value produced by the KDF
    TPM2B_DATA       sequence2B, handle2B;
    // Get proof value
    proof = HierarchyGetProof(contextBlob->hierarchy);

    // Get sequence value in 2B format
    sequence2B.t.size = sizeof(contextBlob->sequence);
    cAssert(sequence2B.t.size <= sizeof(sequence2B.t.buffer));
    MemoryCopy(sequence2B.t.buffer, &contextBlob->sequence, sequence2B.t.size);
    
    // Get handle value in 2B format
    handle2B.t.size = sizeof(contextBlob->savedHandle);
    cAssert(handle2B.t.size <= sizeof(handle2B.t.buffer));
    MemoryCopy(handle2B.t.buffer, &contextBlob->savedHandle, handle2B.t.size);

    // Get the symmetric encryption key size
    symKey->t.size = CONTEXT_ENCRYPT_KEY_BYTES;
    symKeyBits = CONTEXT_ENCRYPT_KEY_BITS;
    // Get the size of the IV for the algorithm
    iv->t.size = CryptGetSymmetricBlockSize(CONTEXT_ENCRYPT_ALG, symKeyBits);
    // KDFa to generate symmetric key and IV value
    CryptKDFa(CONTEXT_INTEGRITY_HASH_ALG, &proof->b, CONTEXT_KEY, &sequence2B.b,
	      &handle2B.b, (symKey->t.size + iv->t.size) * 8, kdfResult, NULL,
	      FALSE);
    // Copy part of the returned value as the key
    pAssert(symKey->t.size <= sizeof(symKey->t.buffer));
    MemoryCopy(symKey->t.buffer, kdfResult, symKey->t.size);
    // Copy the rest as the IV
    pAssert(iv->t.size <= sizeof(iv->t.buffer));
    MemoryCopy(iv->t.buffer, &kdfResult[symKey->t.size], iv->t.size);
    return;
}
/* 7.3.2.2 ComputeContextIntegrity() */
/* Generate the integrity hash for a context It is used by TPM2_ContextSave() to create an integrity
   hash and by TPM2_ContextLoad() to compare an integrity hash */
void
ComputeContextIntegrity(
			TPMS_CONTEXT    *contextBlob,   // IN: context blob
			TPM2B_DIGEST    *integrity      // OUT: integrity
			)
{
    HMAC_STATE          hmacState;
    TPM2B_PROOF         *proof;
    UINT16              integritySize;
    // Get proof value
    proof = HierarchyGetProof(contextBlob->hierarchy);
    // Start HMAC
    integrity->t.size = CryptHmacStart2B(&hmacState, CONTEXT_INTEGRITY_HASH_ALG,
					 &proof->b);
    // Compute integrity size at the beginning of context blob
    integritySize = sizeof(integrity->t.size) + integrity->t.size;
    // Adding total reset counter so that the context cannot be
    // used after a TPM Reset
    CryptDigestUpdateInt(&hmacState.hashState, sizeof(gp.totalResetCount),
			 gp.totalResetCount);
    // If this is a ST_CLEAR object, add the clear count
    // so that this contest cannot be loaded after a TPM Restart
    if(contextBlob->savedHandle == 0x80000002)
	CryptDigestUpdateInt(&hmacState.hashState, sizeof(gr.clearCount),
			     gr.clearCount);
    // Adding sequence number to the HMAC to make sure that it doesn't
    // get changed
    CryptDigestUpdateInt(&hmacState.hashState, sizeof(contextBlob->sequence),
			 contextBlob->sequence);
    // Protect the handle
    CryptDigestUpdateInt(&hmacState.hashState, sizeof(contextBlob->savedHandle),
			 contextBlob->savedHandle);
    // Adding sensitive contextData, skip the leading integrity area
    CryptDigestUpdate(&hmacState.hashState,
		      contextBlob->contextBlob.t.size - integritySize,
		      contextBlob->contextBlob.t.buffer + integritySize);
    // Complete HMAC
    CryptHmacEnd2B(&hmacState, &integrity->b);
    return;
}
/* 7.3.2.3 SequenceDataExport() */
/* This function is used scan through the sequence object and either modify the hash state data for
   export (contextSave) or to import it into the internal format (contextLoad). This function should
   only be called after the sequence object has been copied to the context buffer (contextSave) or
   from the context buffer into the sequence object. The presumption is that the context buffer
   version of the data is the same size as the internal representation so nothing outsize of the
   hash context area gets modified. */
void
SequenceDataExport(
		   HASH_OBJECT         *object,        // IN: an internal hash object
		   HASH_OBJECT_BUFFER  *exportObject   // OUT: a sequence context in a buffer
		   )
{
    // If the hash object is not an event, then only one hash context is needed
    int                   count = (object->attributes.eventSeq) ? HASH_COUNT : 1;
    for(count--; count >= 0; count--)
	{
	    HASH_STATE          *hash = &object->state.hashState[count];
	    size_t               offset = (BYTE *)hash - (BYTE *)object;
	    BYTE                *exportHash = &((BYTE *)exportObject)[offset];
	    CryptHashExportState(hash, (EXPORT_HASH_STATE *)exportHash);
	}
}
/* 7.3.2.4 SequenceDataImport() */
/* This function is used scan through the sequence object and either modify the hash state data for
   export (contextSave) or to import it into the internal format (contextLoad). This function should
   only be called after the sequence object has been copied to the context buffer (contextSave) or
   from the context buffer into the sequence object. The presumption is that the context buffer
   version of the data is the same size as the internal representation so nothing outsize of the
   hash context area gets modified. */
void
SequenceDataImport(
		   HASH_OBJECT         *object,        // IN/OUT: an internal hash object
		   HASH_OBJECT_BUFFER  *exportObject   // IN/OUT: a sequence context in a buffer
		   )
{
    // If the hash object is not an event, then only one hash context is needed
    int                   count = (object->attributes.eventSeq) ? HASH_COUNT : 1;
    for(count--; count >= 0; count--)
	{
	    HASH_STATE          *hash = &object->state.hashState[count];
	    size_t               offset = (BYTE *)hash - (BYTE *)object;
	    BYTE                *importHash = &((BYTE *)exportObject)[offset];
	    //
	    CryptHashImportState(hash, (EXPORT_HASH_STATE *)importHash);
	}
}