encrypt/sign 2048 bit RSA key using another Rsa 2048 bit Key

[Vinod Jacob]

Hi,
  I am using libgcrypt 2048 bit encryption.

what is the maximum size of the buffer that i can encrypt using 2048
bit key.is it 2048 bit ?

 I am getting incorrect values when i try to encrypt a buffer of size(
more that 2048 bit ). Encryption/decryption function is success .But
when i tried to print the decrypted buffer , it is showing different
values. so what i needs to do if ,1 want to encrypt buffer of large
size ? (i know we can encrypt large buffer using AES and encrypt AEs
keys using RSA ).But my requirement is to encrypt large buffer using
RSA .


Let me try to explain what i am trying to do in more detail,

  I have to encrypt/sign Rsa ( 2048 bit) keys using another Rsa  2048 bit Key

say Entity A there is one Rsa Keys A_pub_key & A_sec_key
and say Entity b there is one Rsa keys B_pub_key & B_sec_key

 i want to encrypt A_sec_key using B_pub_key is it possible ? how i
have to do encrypt a RSA key using another RSA key ? Do i need to take
each mpi values and do encryption ? is it posssible to concate each
mpi value and encrypt it?


here is the piece of the code i am using,
==============================
if(gcry_ac_open(&GcryptRsaHd, GCRY_AC_RSA, 0)!=0)
      {
         printf (" Gcrypt RSA Cipher Open : %s\n", gpg_strerror(GcryptErrVal) );
         //return RSA_CIPHER_OPEN_FAILURE ;
      }
      data = gcry_ac_key_data_get(RsaKey);
      for (i = 0; i < gcry_ac_data_length(data); i++)
      {
            gcry_ac_data_get_index(data, 0 , i, &sName[i], &mpiTemp[i]);
            printf(" MPI %s Bits : %d \n" ,sName[i]
,gcry_mpi_get_nbits(mpiTemp[i]));
 GcryptErrVal = gcry_ac_data_encrypt( GcryptRsaHd
,/*GCRY_AC_FLAG_NO_BLINDING*/0,tGcryptRsaPubKey,mpiTemp[i],&GcryptEncryptData[i]);
            if ( GcryptErrVal )
            {
                 printf (" KeyEncryption : %s :%s \n",gpg_strerror(
GcryptErrVal ), gpg_strsource( GcryptErrVal ));
                 gcry_ac_close(GcryptRsaHd);
                 //return SECURITY_FAILURE;
            }
            else
            {
                 printf("KeyEncryption : %s \n",gpg_strerror( GcryptErrVal ));
            }
     }

     printf(":::::::::::key Decryption function ::::::::::::::::::::::::\n");
     GcryptErrVal = gcry_ac_data_new( &GcryptDecryptedData);
     for (i=0 ;i<6; i++)
     {
 GcryptErrVal = gcry_ac_data_decrypt(GcryptRsaHd
,0/*GCRY_AC_FLAG_NO_BLINDING*/,tGcryptRsaSecKey
,&mpiTemp2[i],GcryptEncryptData[i]);
         if ( GcryptErrVal )
         {
           printf (" KeyDecryption : %s :%s \n",gpg_strerror(
GcryptErrVal ), gpg_strsource( GcryptErrVal ));
           //return SECURITY_FAILURE;
         }
         else
         {
           printf (" KeyDecryption : %s  \n",gpg_strerror( GcryptErrVal ));
           printf(" MPI %s Bits : %d \n" ,sName[i]
,gcry_mpi_get_nbits(mpiTemp2[i]));
           if(gcry_mpi_cmp(mpiTemp[i],mpiTemp2[i] )==0)
           {
                  printf ("MPI cmp success \n");
           }
           else
                 printf ("*********MPI CMP FAILURE ***********\n");
           if (gcry_ac_data_set(GcryptDecryptedData,
GCRY_AC_FLAG_COPY,/*RsaKeyMpiNames[i]*/sName[i], mpiTemp2[i]))
           {
             gcry_ac_close(GcryptRsaHd);
             gcry_mpi_release(mpiTemp2[i]);
             //return -3;
           }
          gcry_mpi_release(mpiTemp2[i]);
        }

     }
     gcry_ac_key_init(&GcryptTestKey,GcryptRsaHd,GCRY_AC_KEY_SECRET ,
GcryptDecryptedData);
     GcryptErrVal = gcry_ac_key_test(GcryptRsaHd ,GcryptTestKey );
     if(GcryptErrVal)
     {
          printf ("********** Testing Rsa Secret Key :
%s\n",gpg_strerror(  GcryptErrVal ),gpg_strsource( GcryptErrVal ));
          gcry_ac_close(GcryptRsaHd);
          //return RSA_KEY_TEST_FAILURE;  /* TBC */
     }
     else
        printf ("************Testing Rsa Secret Key :
%s\n",gpg_strerror(  GcryptErrVal ),gpg_strsource( GcryptErrVal ));


 But I am getting out put

 KeyEncryption : Success
  MPI e Bits : 6
 KeyEncryption : Success
  MPI d Bits : 2041
 KeyEncryption : Success
  MPI p Bits : 1024
 KeyEncryption : Success
  MPI q Bits : 1024
 KeyEncryption : Success
  MPI u Bits : 1024
 KeyEncryption : Success
 :::::::::::key Decryption function ::::::::::::::::::::::::
  KeyDecryption : Success
  MPI n Bits : 0
 *********MPI CMP FAILURE ***********
  KeyDecryption : Success
  MPI e Bits : 6
 MPI cmp success
  KeyDecryption : Success
  MPI d Bits : 2041
 MPI cmp success
  KeyDecryption : Success
  MPI p Bits : 1024
 MPI cmp success
  KeyDecryption : Success
  MPI q Bits : 1024
 MPI cmp success
  KeyDecryption : Success
  MPI u Bits : 1024
 MPI cmp success
 ********** Testing Rsa Secret Key : Invalid public key algorithm


 What is the problem ? could some one help me in solving this one  ?

thanks
   Vinod