Here's some sample data and test code to try running through it - if I've made some mistake, I'd be happy to have it pointed out.

// This example is from : http://www.di-mgt.com.au/rsa_alg.html#simpleexample #define TEST_PUBLIC_KEY_EXP "010001"

#define TEST_PUBLIC_KEY_MOD "A9E167983F39D55FF2A093415EA6798985C8355D9A915BFB1D01DA197026170F" \ "BDA522D035856D7A986614415CCFB7B7083B09C991B81969376DF9651E7BD9A9" \ "3324A37F3BBBAF460186363432CB07035952FC858B3104B8CC18081448E64F1C" \ "FB5D60C4E05C1F53D37F53D86901F105F87A70D1BE83C65F38CF1C2CAA6AA7EB"

#define TEST_CRYPTOGRAM "0002257F48FD1F1793B7E5E02306F2D3228F5C95ADF5F31566729F132AA12009" \ "E3FC9B2B475CD6944EF191E3F59545E671E474B555799FE3756099F044964038" \ "B16B2148E9A2F9C6F44BB5C52E3C6C8061CF694145FAFDB24402AD1819EACEDF" \ "4A36C6E4D2CD8FC1D62E5A1268F496004E636AF98E40F3ADCFCCB698F4E80B9F"

#define TEST_RESULT "3D2AB25B1EB667A40F504CC4D778EC399A899C8790EDECEF062CD739492C9CE5" \ "8B92B9ECF32AF4AAC7A61EAEC346449891F49A722378E008EFF0B0A8DBC6E621" \ "EDC90CEC64CF34C640F5B36C48EE9322808AF8F4A0212B28715C76F3CB99AC7E" \ "609787ADCE055839829E0142C44B676D218111FFE69F9D41424E177CBA3A435B"

   HB_hex_string_to_hex_bignum( TEST_PUBLIC_KEY_EXP, &(publicKey.e) );

   HB_hex_string_to_hex_bignum( TEST_PUBLIC_KEY_MOD, &(publicKey.n) );

   HB_int_to_hex_bignum( 0, &privateKey.e );
   HB_int_to_hex_bignum( 0, &privateKey.n );

   HB_hex_string_to_hex_bignum( TEST_CRYPTOGRAM, &rsaOrig );

   rsaDecrypt( &rsaOrig, &rsaDecrypted, &publicKey );

   HB_hex_string_to_hex_bignum( TEST_RESULT, &rsaEncrypted );
   if ( HB_compare( &rsaEncrypted, &rsaDecrypted ) == 0 )
   {
      printf( "Passed!\n" );
   }
   else
   {
      printf( "Failed!\n" );
   }