UINT32 SignData()

in src/tpm_codec.c [302:389]
82 lines of code
9 McCabe index (conditional complexity)

UINT32 SignData(TSS_DEVICE* tpm, TSS_SESSION* sess, BYTE* tokenData, UINT32 tokenSize, BYTE* signatureBuffer, UINT32 sigBufSize)
{
    UINT32 result;
    TPM_RC          rc;
    TPM2B_DIGEST    digest;
    TPM_ALG_ID      idKeyHashAlg = ALG_SHA256_VALUE;
    UINT32          sigSize = TSS_GetDigestSize(idKeyHashAlg); //32
    UINT32          MaxInputBuffer = 0;

    if (sigBufSize < sigSize)
    {
        LogError("Signature buffer size (%uz) is less than required size (%uz)", sigBufSize, sigSize);
        result = sigSize;
    }
    else
    {
        sigBufSize = 0;
        MaxInputBuffer = TSS_GetTpmProperty(tpm, TPM_PT_INPUT_BUFFER); // 1024
        if (tokenSize > MaxInputBuffer) // 68
        {
            TPMI_DH_OBJECT  hSeq = TPM_RH_NULL;
            BYTE           *curPos = tokenData;
            UINT32          bytesLeft = tokenSize;

            rc = TPM2_HMAC_Start(tpm, sess, DPS_ID_KEY_HANDLE, NULL, idKeyHashAlg, &hSeq);
            if (rc != TPM_RC_SUCCESS)
            {
                LogError("Failed to start HMAC sequence %s", TSS_StatusValueName(rc) );
                result = 0;
            }
            else
            {
                bool seq_complete = true;
                // Above condition 'if (tokenSize > MaxInputBuffer)' ensures that the first
                // iteration is always valid.
                do
                {
                    rc = TSS_SequenceUpdate(tpm, sess, hSeq, curPos, MaxInputBuffer);
                    if (rc != TPM_RC_SUCCESS)
                    {
                        LogError("Failed to update HMAC sequence %s", TSS_StatusValueName(rc));
                        seq_complete = false;
                        break;
                    }

                    bytesLeft -= MaxInputBuffer;
                    curPos += MaxInputBuffer;
                } while (bytesLeft > MaxInputBuffer);

                if (seq_complete)
                {
                    rc = TSS_SequenceComplete(tpm, sess, hSeq, curPos, bytesLeft, &digest);
                    if (rc != TPM_RC_SUCCESS)
                    {
                        LogError("Failed to complete HMAC sequence %s", TSS_StatusValueName(rc));
                        result = 0;
                    }
                    else
                    {
                        MemoryCopy(signatureBuffer, digest.t.buffer, sigSize);
                        sigBufSize = sigSize;
                        result = sigBufSize;
                    }
                }
                else
                {
                    result = 0;
                }
            }
        }
        else
        {
            rc = TSS_HMAC(tpm, sess, DPS_ID_KEY_HANDLE, tokenData, tokenSize, &digest);
            if (rc != TPM_RC_SUCCESS)
            {
                LogError("Hashing token data failed %s", TSS_StatusValueName(rc));
                result = 0;
            }
            else
            {
                MemoryCopy(signatureBuffer, digest.t.buffer, sigSize);
                sigBufSize = sigSize;
                result = sigBufSize;
            }
        }
    }
    return result;
}