/********************************************************************************/

/*                    */

/*                  */

/*           Written by Ken Goldman       */

/*           IBM Thomas J. Watson Research Center     */

/*            $Id: Context_spt.c 1273 2018-07-20 18:49:46Z 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_ConextSave() 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(sizeof(contextBlob->sequence) <= sizeof(sequence2B.t.buffer));

    MemoryCopy(sequence2B.t.buffer, &contextBlob->sequence,

         sizeof(contextBlob->sequence));

    // Get handle value in 2B format

    handle2B.t.size = sizeof(contextBlob->savedHandle);

    cAssert(sizeof(contextBlob->savedHandle) <= sizeof(handle2B.t.buffer));

    MemoryCopy(handle2B.t.buffer, &contextBlob->savedHandle,

         sizeof(contextBlob->savedHandle));

    // 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);

  }

}